Supervised PhD theses

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  Messung, Modellierung und Vorhersage der Netzwerkqualität mit Fokus auf das Internet der Dinge (IoT). Herrnleben, Stefan; Thesis; Universität Würzburg. (2024).
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  @phdthesis{Herrnleben2024, author = {Herrnleben, Stefan}, keywords = {descartes}, school = {Universit{\"a}t W{\"u}rzburg}, title = {Messung, Modellierung und Vorhersage der Netzwerkqualit{\"a}t mit Fokus auf das Internet der Dinge (IoT)}, type = {doctoralthesis}, year = 2024 }

  %0 Thesis %1 Herrnleben2024 %A Herrnleben, Stefan %D 2024 %R 10.25972/OPUS-37674 %T Messung, Modellierung und Vorhersage der Netzwerkqualität mit Fokus auf das Internet der Dinge (IoT)

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  Performance Engineering of Serverless Applications and Platforms. Eismann, Simon; Thesis; Universität Würzburg. (2023).
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  @phdthesis{Eismann2023, author = {Eismann, Simon}, keywords = {descartes}, school = {Universit{\"a}t W{\"u}rzburg}, title = {Performance Engineering of Serverless Applications and Platforms}, type = {doctoralthesis}, year = 2023 }

  %0 Thesis %1 Eismann2023 %A Eismann, Simon %D 2023 %T Performance Engineering of Serverless Applications and Platforms

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  Measurement, Modeling, and Emulation of Power Consumption of Distributed Systems. Schmitt, Norbert; (2022, June).
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  @phdthesis{Schmitt_2022, author = {Schmitt, Norbert}, keywords = {power}, month = {06}, title = {Measurement, Modeling, and Emulation of Power Consumption of Distributed Systems}, year = 2022 }

  %0 Thesis %1 Schmitt_2022 %A Schmitt, Norbert %D 2022 %T Measurement, Modeling, and Emulation of Power Consumption of Distributed Systems %U https://opus.bibliothek.uni-wuerzburg.de/frontdoor/index/index/start/2/rows/10/sortfield/score/sortorder/desc/searchtype/simple/query/Norbert+Schmitt/yearfq/2022/docId/27658
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  Self-Aware Optimization of Cyber-Physical Systems in Intelligent Transportation and Logistics Systems. Lesch, Veronika; Thesis; Universität Würzburg. (2022, April).
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  @phdthesis{Le2022-Dissertation, author = {Lesch, Veronika}, keywords = {internet_of_things}, month = {04}, school = {Universität Würzburg}, title = {Self-Aware Optimization of Cyber-Physical Systems in Intelligent Transportation and Logistics Systems}, type = {Dissertation}, year = 2022 }

  %0 Thesis %1 Le2022-Dissertation %A Lesch, Veronika %D 2022 %T Self-Aware Optimization of Cyber-Physical Systems in Intelligent Transportation and Logistics Systems %U https://doi.org/10.25972/OPUS-27228
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  Model Learning for Performance Prediction of Cloud-native Microservice Applications. Grohmann, Johannes; Thesis; Universität Würzburg. (2022, March).

  Distinction
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  One consequence of the recent coronavirus pandemic is increased demand and use of online services around the globe. At the same time, performance requirements for modern technologies are becoming more stringent as users become accustomed to higher standards. These increased performance and availability requirements, coupled with the unpredictable usage growth, are driving an increasing proportion of applications to run on public cloud platforms as they promise better scalability and reliability. With data centers already responsible for about one percent of the world's power consumption, optimizing resource usage is of paramount importance. Simultaneously, meeting the increasing and changing resource and performance requirements is only possible by optimizing resource management without introducing additional overhead. This requires the research and development of new modeling approaches to understand the behavior of running applications with minimal information. However, the emergence of modern software paradigms makes it increasingly difficult to derive such models and renders previous performance modeling techniques infeasible. Modern cloud applications are often deployed as a collection of fine-grained and interconnected components called microservices. Microservice architectures offer massive benefits but also have broad implications for the performance characteristics of the respective systems. In addition, the microservices paradigm is typically paired with a DevOps culture, resulting in frequent application and deployment changes. Such applications are often referred to as cloud-native applications. In summary, the increasing use of ever-changing cloud-hosted microservice applications introduces a number of unique challenges for modeling the performance of modern applications. These include the amount, type, and structure of monitoring data, frequent behavioral changes, or infrastructure variabilities. This violates common assumptions of the state of the art and opens a research gap for our work. In this thesis, we present five techniques for automated learning of performance models for cloud-native software systems. We achieve this by combining machine learning with traditional performance modeling techniques. Unlike previous work, our focus is on cloud-hosted and continuously evolving microservice architectures, so-called cloud-native applications. Therefore, our contributions aim to solve the above challenges to deliver automated performance models with minimal computational overhead and no manual intervention. Depending on the cloud computing model, privacy agreements, or monitoring capabilities of each platform, we identify different scenarios where performance modeling, prediction, and optimization techniques can provide great benefits. Specifically, the contributions of this thesis are as follows: Monitorless: Application-agnostic prediction of performance degradations. To manage application performance with only platform-level monitoring, we propose Monitorless, the first truly application-independent approach to detecting performance degradation. We use machine learning to bridge the gap between platform-level monitoring and application-specific measurements, eliminating the need for application-level monitoring. Monitorless creates a single and holistic resource saturation model that can be used for heterogeneous and untrained applications. Results show that Monitorless infers resource-based performance degradation with 97% accuracy. Moreover, it can achieve similar performance to typical autoscaling solutions, despite using less monitoring information. SuanMing: Predicting performance degradation using tracing. We introduce SuanMing to mitigate performance issues before they impact the user experience. This contribution is applied in scenarios where tracing tools enable application-level monitoring. SuanMing predicts explainable causes of expected performance degradations and prevents performance degradations before they occur. Evaluation results show that SuanMing can predict and pinpoint future performance degradations with an accuracy of over 90%. SARDE: Continuous and autonomous estimation of resource demands. We present SARDE to learn application models for highly variable application deployments. This contribution focuses on the continuous estimation of application resource demands, a key parameter of performance models. SARDE represents an autonomous ensemble estimation technique. It dynamically and continuously optimizes, selects, and executes an ensemble of approaches to estimate resource demands in response to changes in the application or its environment. Through continuous online adaptation, SARDE efficiently achieves an average resource demand estimation error of 15.96% in our evaluation. DepIC: Learning parametric dependencies from monitoring data. DepIC utilizes feature selection techniques in combination with an ensemble regression approach to automatically identify and characterize parametric dependencies. Although parametric dependencies can massively improve the accuracy of performance models, DepIC is the first approach to automatically learn such parametric dependencies from passive monitoring data streams. Our evaluation shows that DepIC achieves 91.7% precision in identifying dependencies and reduces the characterization prediction error by 30% compared to the best individual approach. Baloo: Modeling the configuration space of databases. To study the impact of different configurations within distributed DBMSs, we introduce Baloo. Our last contribution models the configuration space of databases considering measurement variabilities in the cloud. More specifically, Baloo dynamically estimates the required benchmarking measurements and automatically builds a configuration space model of a given DBMS. Our evaluation of Baloo on a dataset consisting of 900 configuration points shows that the framework achieves a prediction error of less than 11% while saving up to 80% of the measurement effort. Although the contributions themselves are orthogonally aligned, taken together they provide a holistic approach to performance management of modern cloud-native microservice applications. Our contributions are a significant step forward as they specifically target novel and cloud-native software development and operation paradigms, surpassing the capabilities and limitations of previous approaches. In addition, the research presented in this paper also has a significant impact on the industry, as the contributions were developed in collaboration with research teams from Nokia Bell Labs, Huawei, and Google. Overall, our solutions open up new possibilities for managing and optimizing cloud applications and improve cost and energy efficiency.

  @phdthesis{Gr2022-Dissertation, abstract = {One consequence of the recent coronavirus pandemic is increased demand and use of online services around the globe. At the same time, performance requirements for modern technologies are becoming more stringent as users become accustomed to higher standards. These increased performance and availability requirements, coupled with the unpredictable usage growth, are driving an increasing proportion of applications to run on public cloud platforms as they promise better scalability and reliability. With data centers already responsible for about one percent of the world's power consumption, optimizing resource usage is of paramount importance. Simultaneously, meeting the increasing and changing resource and performance requirements is only possible by optimizing resource management without introducing additional overhead. This requires the research and development of new modeling approaches to understand the behavior of running applications with minimal information. However, the emergence of modern software paradigms makes it increasingly difficult to derive such models and renders previous performance modeling techniques infeasible. Modern cloud applications are often deployed as a collection of fine-grained and interconnected components called microservices. Microservice architectures offer massive benefits but also have broad implications for the performance characteristics of the respective systems. In addition, the microservices paradigm is typically paired with a DevOps culture, resulting in frequent application and deployment changes. Such applications are often referred to as cloud-native applications. In summary, the increasing use of ever-changing cloud-hosted microservice applications introduces a number of unique challenges for modeling the performance of modern applications. These include the amount, type, and structure of monitoring data, frequent behavioral changes, or infrastructure variabilities. This violates common assumptions of the state of the art and opens a research gap for our work. In this thesis, we present five techniques for automated learning of performance models for cloud-native software systems. We achieve this by combining machine learning with traditional performance modeling techniques. Unlike previous work, our focus is on cloud-hosted and continuously evolving microservice architectures, so-called cloud-native applications. Therefore, our contributions aim to solve the above challenges to deliver automated performance models with minimal computational overhead and no manual intervention. Depending on the cloud computing model, privacy agreements, or monitoring capabilities of each platform, we identify different scenarios where performance modeling, prediction, and optimization techniques can provide great benefits. Specifically, the contributions of this thesis are as follows: Monitorless: Application-agnostic prediction of performance degradations. To manage application performance with only platform-level monitoring, we propose Monitorless, the first truly application-independent approach to detecting performance degradation. We use machine learning to bridge the gap between platform-level monitoring and application-specific measurements, eliminating the need for application-level monitoring. Monitorless creates a single and holistic resource saturation model that can be used for heterogeneous and untrained applications. Results show that Monitorless infers resource-based performance degradation with 97% accuracy. Moreover, it can achieve similar performance to typical autoscaling solutions, despite using less monitoring information. SuanMing: Predicting performance degradation using tracing. We introduce SuanMing to mitigate performance issues before they impact the user experience. This contribution is applied in scenarios where tracing tools enable application-level monitoring. SuanMing predicts explainable causes of expected performance degradations and prevents performance degradations before they occur. Evaluation results show that SuanMing can predict and pinpoint future performance degradations with an accuracy of over 90%. SARDE: Continuous and autonomous estimation of resource demands. We present SARDE to learn application models for highly variable application deployments. This contribution focuses on the continuous estimation of application resource demands, a key parameter of performance models. SARDE represents an autonomous ensemble estimation technique. It dynamically and continuously optimizes, selects, and executes an ensemble of approaches to estimate resource demands in response to changes in the application or its environment. Through continuous online adaptation, SARDE efficiently achieves an average resource demand estimation error of 15.96% in our evaluation. DepIC: Learning parametric dependencies from monitoring data. DepIC utilizes feature selection techniques in combination with an ensemble regression approach to automatically identify and characterize parametric dependencies. Although parametric dependencies can massively improve the accuracy of performance models, DepIC is the first approach to automatically learn such parametric dependencies from passive monitoring data streams. Our evaluation shows that DepIC achieves 91.7% precision in identifying dependencies and reduces the characterization prediction error by 30% compared to the best individual approach. Baloo: Modeling the configuration space of databases. To study the impact of different configurations within distributed DBMSs, we introduce Baloo. Our last contribution models the configuration space of databases considering measurement variabilities in the cloud. More specifically, Baloo dynamically estimates the required benchmarking measurements and automatically builds a configuration space model of a given DBMS. Our evaluation of Baloo on a dataset consisting of 900 configuration points shows that the framework achieves a prediction error of less than 11% while saving up to 80% of the measurement effort. Although the contributions themselves are orthogonally aligned, taken together they provide a holistic approach to performance management of modern cloud-native microservice applications. Our contributions are a significant step forward as they specifically target novel and cloud-native software development and operation paradigms, surpassing the capabilities and limitations of previous approaches. In addition, the research presented in this paper also has a significant impact on the industry, as the contributions were developed in collaboration with research teams from Nokia Bell Labs, Huawei, and Google. Overall, our solutions open up new possibilities for managing and optimizing cloud applications and improve cost and energy efficiency.}, author = {Grohmann, Johannes}, keywords = {performance}, month = {03}, note = {Distinction}, school = {Universität Würzburg}, title = {Model Learning for Performance Prediction of Cloud-native Microservice Applications}, type = {Dissertation}, year = 2022 }

  %0 Thesis %1 Gr2022-Dissertation %A Grohmann, Johannes %D 2022 %T Model Learning for Performance Prediction of Cloud-native Microservice Applications %U https://opus.bibliothek.uni-wuerzburg.de/frontdoor/index/index/docId/26160 %X One consequence of the recent coronavirus pandemic is increased demand and use of online services around the globe. At the same time, performance requirements for modern technologies are becoming more stringent as users become accustomed to higher standards. These increased performance and availability requirements, coupled with the unpredictable usage growth, are driving an increasing proportion of applications to run on public cloud platforms as they promise better scalability and reliability. With data centers already responsible for about one percent of the world's power consumption, optimizing resource usage is of paramount importance. Simultaneously, meeting the increasing and changing resource and performance requirements is only possible by optimizing resource management without introducing additional overhead. This requires the research and development of new modeling approaches to understand the behavior of running applications with minimal information. However, the emergence of modern software paradigms makes it increasingly difficult to derive such models and renders previous performance modeling techniques infeasible. Modern cloud applications are often deployed as a collection of fine-grained and interconnected components called microservices. Microservice architectures offer massive benefits but also have broad implications for the performance characteristics of the respective systems. In addition, the microservices paradigm is typically paired with a DevOps culture, resulting in frequent application and deployment changes. Such applications are often referred to as cloud-native applications. In summary, the increasing use of ever-changing cloud-hosted microservice applications introduces a number of unique challenges for modeling the performance of modern applications. These include the amount, type, and structure of monitoring data, frequent behavioral changes, or infrastructure variabilities. This violates common assumptions of the state of the art and opens a research gap for our work. In this thesis, we present five techniques for automated learning of performance models for cloud-native software systems. We achieve this by combining machine learning with traditional performance modeling techniques. Unlike previous work, our focus is on cloud-hosted and continuously evolving microservice architectures, so-called cloud-native applications. Therefore, our contributions aim to solve the above challenges to deliver automated performance models with minimal computational overhead and no manual intervention. Depending on the cloud computing model, privacy agreements, or monitoring capabilities of each platform, we identify different scenarios where performance modeling, prediction, and optimization techniques can provide great benefits. Specifically, the contributions of this thesis are as follows: Monitorless: Application-agnostic prediction of performance degradations. To manage application performance with only platform-level monitoring, we propose Monitorless, the first truly application-independent approach to detecting performance degradation. We use machine learning to bridge the gap between platform-level monitoring and application-specific measurements, eliminating the need for application-level monitoring. Monitorless creates a single and holistic resource saturation model that can be used for heterogeneous and untrained applications. Results show that Monitorless infers resource-based performance degradation with 97% accuracy. Moreover, it can achieve similar performance to typical autoscaling solutions, despite using less monitoring information. SuanMing: Predicting performance degradation using tracing. We introduce SuanMing to mitigate performance issues before they impact the user experience. This contribution is applied in scenarios where tracing tools enable application-level monitoring. SuanMing predicts explainable causes of expected performance degradations and prevents performance degradations before they occur. Evaluation results show that SuanMing can predict and pinpoint future performance degradations with an accuracy of over 90%. SARDE: Continuous and autonomous estimation of resource demands. We present SARDE to learn application models for highly variable application deployments. This contribution focuses on the continuous estimation of application resource demands, a key parameter of performance models. SARDE represents an autonomous ensemble estimation technique. It dynamically and continuously optimizes, selects, and executes an ensemble of approaches to estimate resource demands in response to changes in the application or its environment. Through continuous online adaptation, SARDE efficiently achieves an average resource demand estimation error of 15.96% in our evaluation. DepIC: Learning parametric dependencies from monitoring data. DepIC utilizes feature selection techniques in combination with an ensemble regression approach to automatically identify and characterize parametric dependencies. Although parametric dependencies can massively improve the accuracy of performance models, DepIC is the first approach to automatically learn such parametric dependencies from passive monitoring data streams. Our evaluation shows that DepIC achieves 91.7% precision in identifying dependencies and reduces the characterization prediction error by 30% compared to the best individual approach. Baloo: Modeling the configuration space of databases. To study the impact of different configurations within distributed DBMSs, we introduce Baloo. Our last contribution models the configuration space of databases considering measurement variabilities in the cloud. More specifically, Baloo dynamically estimates the required benchmarking measurements and automatically builds a configuration space model of a given DBMS. Our evaluation of Baloo on a dataset consisting of 900 configuration points shows that the framework achieves a prediction error of less than 11% while saving up to 80% of the measurement effort. Although the contributions themselves are orthogonally aligned, taken together they provide a holistic approach to performance management of modern cloud-native microservice applications. Our contributions are a significant step forward as they specifically target novel and cloud-native software development and operation paradigms, surpassing the capabilities and limitations of previous approaches. In addition, the research presented in this paper also has a significant impact on the industry, as the contributions were developed in collaboration with research teams from Nokia Bell Labs, Huawei, and Google. Overall, our solutions open up new possibilities for managing and optimizing cloud applications and improve cost and energy efficiency.
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  Proactive Critical Event Prediction based on Monitoring Data with Focus on Technical Systems. Züfle, Marwin Otto; Thesis; Universität Würzburg. (2022).
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  @phdthesis{Zuefle2022, author = {Z{\"u}fle, Marwin Otto}, keywords = {descartes}, school = {Universit{\"a}t W{\"u}rzburg}, title = {Proactive Critical Event Prediction based on Monitoring Data with Focus on Technical Systems}, type = {doctoralthesis}, year = 2022 }

  %0 Thesis %1 Zuefle2022 %A Züfle, Marwin Otto %D 2022 %T Proactive Critical Event Prediction based on Monitoring Data with Focus on Technical Systems

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  Attack-aware Security Function Management. Iffländer, Lukas; Thesis; Universität Würzburg. (2021, January).
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  Over the last decades, cybersecurity has become an increasingly important issue. Between 2019 and 2011 alone, the losses from cyberattacks in the United States grew by 6217%. At the same time, attacks became not only more intensive but also more and more versatile and diverse. Cybersecurity has become everyone’s concern. Today, service providers require sophisticated and extensive security infrastructures comprising many security functions dedicated to various cyberattacks. Still, attacks become more violent to a level where infrastructures can no longer keep up. Simply scaling up is no longer sufficient. To address this challenge, in a whitepaper, the Cloud Security Alliance (CSA) proposed multiple work packages for security infrastructure, leveraging the possibilities of Software-defined Networking (SDN) and Network Function Virtualization (NFV). Security functions require a more sophisticated modeling approach than regular network functions. Notably, the property to drop packets deemed malicious has a significant impact on Security Service Function Chains (SSFCs)—service chains consisting of multiple security functions to protect against multiple at- tack vectors. Under attack, the order of these chains influences the end-to-end system performance depending on the attack type. Unfortunately, it is hard to predict the attack composition at system design time. Thus, we make a case for dynamic attack-aware SSFC reordering. Also, we tackle the issues of the lack of integration between security functions and the surrounding network infrastructure, the insufficient use of short term CPU frequency boosting, and the lack of Intrusion Detection and Prevention Systems (IDPS) against database ransomware attacks. Current works focus on characterizing the performance of security functions and their behavior under overload without considering the surrounding infrastructure. Other works aim at replacing security functions using network infrastructure features but do not consider integrating security functions within the network. Further publications deal with using SDN for security or how to deal with new vulnerabilities introduced through SDN. However, they do not take security function performance into account. NFV is a popular field for research dealing with frameworks, benchmarking methods, the combination with SDN, and implementing security functions as Virtualized Network Functions (VNFs). Research in this area brought forth the concept of Service Function Chains (SFCs) that chain multiple network functions after one another. Nevertheless, they still do not consider the specifics of security functions. The mentioned CSA whitepaper proposes many valuable ideas but leaves their realization open to others. This thesis presents solutions to increase the performance of single security functions using SDN, performance modeling, a framework for attack-aware SSFC reordering, a solution to make better use of CPU frequency boosting, and an IDPS against database ransomware. Specifically, the primary contributions of this work are: • We present approaches to dynamically bypass Intrusion Detection Systems (IDS) in order to increase their performance without reducing the security level. To this end, we develop and implement three SDN-based approaches (two dynamic and one static). We evaluate the proposed approaches regarding security and performance and show that they significantly increase the performance com- pared to an inline IDS without significant security deficits. We show that using software switches can further increase the performance of the dynamic approaches up to a point where they can eliminate any throughput drawbacks when using the IDS. • We design a DDoS Protection System (DPS) against TCP SYN flood at tacks in the form of a VNF that works inside an SDN-enabled network. This solution eliminates known scalability and performance drawbacks of existing solutions for this attack type. Then, we evaluate this solution showing that it correctly handles the connection establishment and present solutions for an observed issue. Next, we evaluate the performance showing that our solution increases performance up to three times. Parallelization and parameter tuning yields another 76% performance boost. Based on these findings, we discuss optimal deployment strategies. • We introduce the idea of attack-aware SSFC reordering and explain its impact in a theoretical scenario. Then, we discuss the required information to perform this process. We validate our claim of the importance of the SSFC order by analyzing the behavior of single security functions and SSFCs. Based on the results, we conclude that there is a massive impact on the performance up to three orders of magnitude, and we find contradicting optimal orders for different workloads. Thus, we demonstrate the need for dynamic reordering. Last, we develop a model for SSFC regarding traffic composition and resource demands. We classify the traffic into multiple classes and model the effect of single security functions on the traffic and their generated resource demands as functions of the incoming network traffic. Based on our model, we propose three approaches to determine optimal orders for reordering. • We implement a framework for attack-aware SSFC reordering based on this knowledge. The framework places all security functions inside an SDN-enabled network and reorders them using SDN flows. Our evaluation shows that the framework can enforce all routes as desired. It correctly adapts to all attacks and returns to the original state after the attacks cease. We find possible security issues at the moment of reordering and present solutions to eliminate them. • Next, we design and implement an approach to load balance servers while taking into account their ability to go into a state of Central Processing Unit (CPU) frequency boost. To this end, the approach collects temperature information from available hosts and places services on the host that can attain the boosted mode the longest. We evaluate this approach and show its effectiveness. For high load scenarios, the approach increases the overall performance and the performance per watt. Even better results show up for low load workloads, where not only all performance metrics improve but also the temperatures and total power consumption decrease. • Last, we design an IDPS protecting against database ransomware attacks that comprise multiple queries to attain their goal. Our solution models these attacks using a Colored Petri Net (CPN). A proof-of-concept implementation shows that our approach is capable of detecting attacks without creating false positives for benign scenarios. Furthermore, our solution creates only a small performance impact. Our contributions can help to improve the performance of security infrastructures. We see multiple application areas from data center operators over software and hardware developers to security and performance researchers. Most of the above-listed contributions found use in several research publications. Regarding future work, we see the need to better integrate SDN-enabled security functions and SSFC reordering in data center networks. Future SSFC should discriminate between different traffic types, and security frameworks should support automatically learning models for security functions. We see the need to consider energy efficiency when regarding SSFCs and take CPU boosting technologies into account when designing performance models as well as placement, scaling, and deployment strategies. Last, for a faster adaptation against recent ransomware attacks, we propose machine-assisted learning for database IDPS signatures.

  @phdthesis{ifflander2021attackaware, abstract = {Over the last decades, cybersecurity has become an increasingly important issue. Between 2019 and 2011 alone, the losses from cyberattacks in the United States grew by 6217%. At the same time, attacks became not only more intensive but also more and more versatile and diverse. Cybersecurity has become everyone’s concern. Today, service providers require sophisticated and extensive security infrastructures comprising many security functions dedicated to various cyberattacks. Still, attacks become more violent to a level where infrastructures can no longer keep up. Simply scaling up is no longer sufficient. To address this challenge, in a whitepaper, the Cloud Security Alliance (CSA) proposed multiple work packages for security infrastructure, leveraging the possibilities of Software-defined Networking (SDN) and Network Function Virtualization (NFV). Security functions require a more sophisticated modeling approach than regular network functions. Notably, the property to drop packets deemed malicious has a significant impact on Security Service Function Chains (SSFCs)—service chains consisting of multiple security functions to protect against multiple at- tack vectors. Under attack, the order of these chains influences the end-to-end system performance depending on the attack type. Unfortunately, it is hard to predict the attack composition at system design time. Thus, we make a case for dynamic attack-aware SSFC reordering. Also, we tackle the issues of the lack of integration between security functions and the surrounding network infrastructure, the insufficient use of short term CPU frequency boosting, and the lack of Intrusion Detection and Prevention Systems (IDPS) against database ransomware attacks. Current works focus on characterizing the performance of security functions and their behavior under overload without considering the surrounding infrastructure. Other works aim at replacing security functions using network infrastructure features but do not consider integrating security functions within the network. Further publications deal with using SDN for security or how to deal with new vulnerabilities introduced through SDN. However, they do not take security function performance into account. NFV is a popular field for research dealing with frameworks, benchmarking methods, the combination with SDN, and implementing security functions as Virtualized Network Functions (VNFs). Research in this area brought forth the concept of Service Function Chains (SFCs) that chain multiple network functions after one another. Nevertheless, they still do not consider the specifics of security functions. The mentioned CSA whitepaper proposes many valuable ideas but leaves their realization open to others. This thesis presents solutions to increase the performance of single security functions using SDN, performance modeling, a framework for attack-aware SSFC reordering, a solution to make better use of CPU frequency boosting, and an IDPS against database ransomware. Specifically, the primary contributions of this work are: • We present approaches to dynamically bypass Intrusion Detection Systems (IDS) in order to increase their performance without reducing the security level. To this end, we develop and implement three SDN-based approaches (two dynamic and one static). We evaluate the proposed approaches regarding security and performance and show that they significantly increase the performance com- pared to an inline IDS without significant security deficits. We show that using software switches can further increase the performance of the dynamic approaches up to a point where they can eliminate any throughput drawbacks when using the IDS. • We design a DDoS Protection System (DPS) against TCP SYN flood at tacks in the form of a VNF that works inside an SDN-enabled network. This solution eliminates known scalability and performance drawbacks of existing solutions for this attack type. Then, we evaluate this solution showing that it correctly handles the connection establishment and present solutions for an observed issue. Next, we evaluate the performance showing that our solution increases performance up to three times. Parallelization and parameter tuning yields another 76% performance boost. Based on these findings, we discuss optimal deployment strategies. • We introduce the idea of attack-aware SSFC reordering and explain its impact in a theoretical scenario. Then, we discuss the required information to perform this process. We validate our claim of the importance of the SSFC order by analyzing the behavior of single security functions and SSFCs. Based on the results, we conclude that there is a massive impact on the performance up to three orders of magnitude, and we find contradicting optimal orders for different workloads. Thus, we demonstrate the need for dynamic reordering. Last, we develop a model for SSFC regarding traffic composition and resource demands. We classify the traffic into multiple classes and model the effect of single security functions on the traffic and their generated resource demands as functions of the incoming network traffic. Based on our model, we propose three approaches to determine optimal orders for reordering. • We implement a framework for attack-aware SSFC reordering based on this knowledge. The framework places all security functions inside an SDN-enabled network and reorders them using SDN flows. Our evaluation shows that the framework can enforce all routes as desired. It correctly adapts to all attacks and returns to the original state after the attacks cease. We find possible security issues at the moment of reordering and present solutions to eliminate them. • Next, we design and implement an approach to load balance servers while taking into account their ability to go into a state of Central Processing Unit (CPU) frequency boost. To this end, the approach collects temperature information from available hosts and places services on the host that can attain the boosted mode the longest. We evaluate this approach and show its effectiveness. For high load scenarios, the approach increases the overall performance and the performance per watt. Even better results show up for low load workloads, where not only all performance metrics improve but also the temperatures and total power consumption decrease. • Last, we design an IDPS protecting against database ransomware attacks that comprise multiple queries to attain their goal. Our solution models these attacks using a Colored Petri Net (CPN). A proof-of-concept implementation shows that our approach is capable of detecting attacks without creating false positives for benign scenarios. Furthermore, our solution creates only a small performance impact. Our contributions can help to improve the performance of security infrastructures. We see multiple application areas from data center operators over software and hardware developers to security and performance researchers. Most of the above-listed contributions found use in several research publications. Regarding future work, we see the need to better integrate SDN-enabled security functions and SSFC reordering in data center networks. Future SSFC should discriminate between different traffic types, and security frameworks should support automatically learning models for security functions. We see the need to consider energy efficiency when regarding SSFCs and take CPU boosting technologies into account when designing performance models as well as placement, scaling, and deployment strategies. Last, for a faster adaptation against recent ransomware attacks, we propose machine-assisted learning for database IDPS signatures.}, author = {Iffl{\"a}nder, Lukas}, keywords = {security}, month = {01}, school = {Universit{\"a}t W{\"u}rzburg}, title = {Attack-aware Security Function Management}, type = {doctoralthesis}, year = 2021 }

  %0 Thesis %1 ifflander2021attackaware %A Iffländer, Lukas %D 2021 %T Attack-aware Security Function Management %X Over the last decades, cybersecurity has become an increasingly important issue. Between 2019 and 2011 alone, the losses from cyberattacks in the United States grew by 6217%. At the same time, attacks became not only more intensive but also more and more versatile and diverse. Cybersecurity has become everyone’s concern. Today, service providers require sophisticated and extensive security infrastructures comprising many security functions dedicated to various cyberattacks. Still, attacks become more violent to a level where infrastructures can no longer keep up. Simply scaling up is no longer sufficient. To address this challenge, in a whitepaper, the Cloud Security Alliance (CSA) proposed multiple work packages for security infrastructure, leveraging the possibilities of Software-defined Networking (SDN) and Network Function Virtualization (NFV). Security functions require a more sophisticated modeling approach than regular network functions. Notably, the property to drop packets deemed malicious has a significant impact on Security Service Function Chains (SSFCs)—service chains consisting of multiple security functions to protect against multiple at- tack vectors. Under attack, the order of these chains influences the end-to-end system performance depending on the attack type. Unfortunately, it is hard to predict the attack composition at system design time. Thus, we make a case for dynamic attack-aware SSFC reordering. Also, we tackle the issues of the lack of integration between security functions and the surrounding network infrastructure, the insufficient use of short term CPU frequency boosting, and the lack of Intrusion Detection and Prevention Systems (IDPS) against database ransomware attacks. Current works focus on characterizing the performance of security functions and their behavior under overload without considering the surrounding infrastructure. Other works aim at replacing security functions using network infrastructure features but do not consider integrating security functions within the network. Further publications deal with using SDN for security or how to deal with new vulnerabilities introduced through SDN. However, they do not take security function performance into account. NFV is a popular field for research dealing with frameworks, benchmarking methods, the combination with SDN, and implementing security functions as Virtualized Network Functions (VNFs). Research in this area brought forth the concept of Service Function Chains (SFCs) that chain multiple network functions after one another. Nevertheless, they still do not consider the specifics of security functions. The mentioned CSA whitepaper proposes many valuable ideas but leaves their realization open to others. This thesis presents solutions to increase the performance of single security functions using SDN, performance modeling, a framework for attack-aware SSFC reordering, a solution to make better use of CPU frequency boosting, and an IDPS against database ransomware. Specifically, the primary contributions of this work are: • We present approaches to dynamically bypass Intrusion Detection Systems (IDS) in order to increase their performance without reducing the security level. To this end, we develop and implement three SDN-based approaches (two dynamic and one static). We evaluate the proposed approaches regarding security and performance and show that they significantly increase the performance com- pared to an inline IDS without significant security deficits. We show that using software switches can further increase the performance of the dynamic approaches up to a point where they can eliminate any throughput drawbacks when using the IDS. • We design a DDoS Protection System (DPS) against TCP SYN flood at tacks in the form of a VNF that works inside an SDN-enabled network. This solution eliminates known scalability and performance drawbacks of existing solutions for this attack type. Then, we evaluate this solution showing that it correctly handles the connection establishment and present solutions for an observed issue. Next, we evaluate the performance showing that our solution increases performance up to three times. Parallelization and parameter tuning yields another 76% performance boost. Based on these findings, we discuss optimal deployment strategies. • We introduce the idea of attack-aware SSFC reordering and explain its impact in a theoretical scenario. Then, we discuss the required information to perform this process. We validate our claim of the importance of the SSFC order by analyzing the behavior of single security functions and SSFCs. Based on the results, we conclude that there is a massive impact on the performance up to three orders of magnitude, and we find contradicting optimal orders for different workloads. Thus, we demonstrate the need for dynamic reordering. Last, we develop a model for SSFC regarding traffic composition and resource demands. We classify the traffic into multiple classes and model the effect of single security functions on the traffic and their generated resource demands as functions of the incoming network traffic. Based on our model, we propose three approaches to determine optimal orders for reordering. • We implement a framework for attack-aware SSFC reordering based on this knowledge. The framework places all security functions inside an SDN-enabled network and reorders them using SDN flows. Our evaluation shows that the framework can enforce all routes as desired. It correctly adapts to all attacks and returns to the original state after the attacks cease. We find possible security issues at the moment of reordering and present solutions to eliminate them. • Next, we design and implement an approach to load balance servers while taking into account their ability to go into a state of Central Processing Unit (CPU) frequency boost. To this end, the approach collects temperature information from available hosts and places services on the host that can attain the boosted mode the longest. We evaluate this approach and show its effectiveness. For high load scenarios, the approach increases the overall performance and the performance per watt. Even better results show up for low load workloads, where not only all performance metrics improve but also the temperatures and total power consumption decrease. • Last, we design an IDPS protecting against database ransomware attacks that comprise multiple queries to attain their goal. Our solution models these attacks using a Colored Petri Net (CPN). A proof-of-concept implementation shows that our approach is capable of detecting attacks without creating false positives for benign scenarios. Furthermore, our solution creates only a small performance impact. Our contributions can help to improve the performance of security infrastructures. We see multiple application areas from data center operators over software and hardware developers to security and performance researchers. Most of the above-listed contributions found use in several research publications. Regarding future work, we see the need to better integrate SDN-enabled security functions and SSFC reordering in data center networks. Future SSFC should discriminate between different traffic types, and security frameworks should support automatically learning models for security functions. We see the need to consider energy efficiency when regarding SSFCs and take CPU boosting technologies into account when designing performance models as well as placement, scaling, and deployment strategies. Last, for a faster adaptation against recent ransomware attacks, we propose machine-assisted learning for database IDPS signatures.
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  Automated Hybrid Time Series Forecasting: Design, Benchmarking, and Use Cases. Bauer, André; Thesis; Universität Würzburg. (2021).
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  @phdthesis{Bauer2021-phdthesis, author = {Bauer, Andr{\'e}}, keywords = {descartes}, school = {Universit{\"a}t W{\"u}rzburg}, title = {Automated Hybrid Time Series Forecasting: Design, Benchmarking, and Use Cases}, type = {doctoralthesis}, year = 2021 }

  %0 Thesis %1 Bauer2021-phdthesis %A Bauer, André %D 2021 %T Automated Hybrid Time Series Forecasting: Design, Benchmarking, and Use Cases

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  Measuring, Rating, and Predicting the Energy Efficiency of Servers. von Kistowski, Jóakim; Thesis; University of Würzburg, Germany. (2019, March).
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  @phdthesis{Kistowski2019-phd, author = {von Kistowski, J{\'o}akim}, keywords = {Power}, month = {03}, school = {University of W{\"u}rzburg, Germany}, title = {Measuring, Rating, and Predicting the Energy Efficiency of Servers}, year = 2019 }

  %0 Thesis %1 Kistowski2019-phd %A von Kistowski, Jóakim %D 2019 %T Measuring, Rating, and Predicting the Energy Efficiency of Servers %U https://opus.bibliothek.uni-wuerzburg.de/frontdoor/index/index/docId/17847
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  Automation in Software Performance Engineering Based on a Declarative Specification of Concerns. Walter, Jürgen Christian; Thesis; Universität Würzburg. (2019).
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  @phdthesis{Walter2018-phd, author = {Walter, J{\"u}rgen Christian}, keywords = {PMX}, school = {Universit{\"a}t W{\"u}rzburg}, title = {Automation in Software Performance Engineering Based on a Declarative Specification of Concerns}, type = {doctoralthesis}, year = 2019 }

  %0 Thesis %1 Walter2018-phd %A Walter, Jürgen Christian %D 2019 %T Automation in Software Performance Engineering Based on a Declarative Specification of Concerns %U https://opus.bibliothek.uni-wuerzburg.de/frontdoor/index/index/docId/18090

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  Methods and Benchmarks for Auto-Scaling Mechanisms in Elastic Cloud Environments. Herbst, Nikolas; Thesis; University of Würzburg, Germany. (2018, July).

  Distinction, SPEC Kaivalya Dixit Distinguished Dissertation Award 2018
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  @phdthesis{Herbst2018-phd, author = {Herbst, Nikolas}, keywords = {SPEC}, month = {07}, note = {<b>{Distinction, SPEC Kaivalya Dixit Distinguished Dissertation Award 2018}</b>}, school = {University of W{\"u}rzburg, Germany}, title = {Methods and Benchmarks for Auto-Scaling Mechanisms in Elastic Cloud Environments}, year = 2018 }

  %0 Thesis %1 Herbst2018-phd %A Herbst, Nikolas %D 2018 %T Methods and Benchmarks for Auto-Scaling Mechanisms in Elastic Cloud Environments %U https://opus.bibliothek.uni-wuerzburg.de/frontdoor/index/index/docId/16431

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  Self-Aware Resource Management in Virtualized Data Centers. Spinner, Simon; Thesis; University of Würzburg, Germany. (2017, July).
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  @phdthesis{Spinner2017-phd, author = {Spinner, Simon}, keywords = {descartes}, month = {07}, school = {University of W{\"u}rzburg, Germany}, title = {Self-Aware Resource Management in Virtualized Data Centers}, year = 2017 }

  %0 Thesis %1 Spinner2017-phd %A Spinner, Simon %D 2017 %T Self-Aware Resource Management in Virtualized Data Centers %U https://opus.bibliothek.uni-wuerzburg.de/frontdoor/index/index/docId/15375
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  Flexible Modeling of Data Center Networks for Capacity Management. Rygielski, Piotr; Thesis; University of Würzburg, Germany. (2017, March).
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  @phdthesis{Rygielski2017-phd, author = {Rygielski, Piotr}, keywords = {DNI}, month = {03}, school = {University of W{\"u}rzburg, Germany}, title = {Flexible Modeling of Data Center Networks for Capacity Management}, year = 2017 }

  %0 Thesis %1 Rygielski2017-phd %A Rygielski, Piotr %D 2017 %T Flexible Modeling of Data Center Networks for Capacity Management %U https://opus.bibliothek.uni-wuerzburg.de/frontdoor/index/index/docId/14623

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  Evaluation of Intrusion Detection Systems in Virtualized Environments. Milenkoski, Aleksandar; Thesis; University of Würzburg, Germany. (2016, November).

  SPEC Kaivalya Dixit Distinguished Dissertation Award 2017
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  @phdthesis{Milenkoski2016-phd, author = {Milenkoski, Aleksandar}, keywords = {descartes}, month = 11, note = {{SPEC Kaivalya Dixit Distinguished Dissertation Award 2017}}, school = {University of W{\"u}rzburg, Germany}, title = {Evaluation of Intrusion Detection Systems in Virtualized Environments}, year = 2016 }

  %0 Thesis %1 Milenkoski2016-phd %A Milenkoski, Aleksandar %D 2016 %T Evaluation of Intrusion Detection Systems in Virtualized Environments %U https://opus.bibliothek.uni-wuerzburg.de/frontdoor/index/index/docId/14184

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  Performance Isolation in Multi-Tenant Applications. Krebs, Rouven; Thesis; Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany. (2015, August).
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  @phdthesis{Krebs2015-phd, author = {Krebs, Rouven}, keywords = {descartes}, month = {08}, school = {Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany}, title = {Performance Isolation in Multi-Tenant Applications}, year = 2015 }

  %0 Thesis %1 Krebs2015-phd %A Krebs, Rouven %D 2015 %T Performance Isolation in Multi-Tenant Applications
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  Modeling and Prediction of I/O Performance in Virtualized Environments. Noorshams, Qais; Thesis; Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany. (2015, February).
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  @phdthesis{Noorshams2015-phd, author = {Noorshams, Qais}, keywords = {descartes}, month = {02}, school = {Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany}, title = {Modeling and Prediction of I/O Performance in Virtualized Environments}, year = 2015 }

  %0 Thesis %1 Noorshams2015-phd %A Noorshams, Qais %D 2015 %T Modeling and Prediction of I/O Performance in Virtualized Environments %U http://primo.bibliothek.kit.edu/primo_library/libweb/action/dlDisplay.do?vid=KIT&docId=KITSRCE1000046750&tab=kit_evastar&srt=date

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  Architecture-Level Software Performance Models for Online Performance Prediction. Brosig, Fabian; Thesis; Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany. (2014, July).

  Distinction
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  @phdthesis{Brosig2014-KIT-OnlinePerformancePrediction, author = {Brosig, Fabian}, keywords = {Prediction}, month = {07}, note = {<b>{Distinction}</b>}, school = {Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany}, title = {Architecture-Level Software Performance Models for Online Performance Prediction}, year = 2014 }

  %0 Thesis %1 Brosig2014-KIT-OnlinePerformancePrediction %A Brosig, Fabian %D 2014 %T Architecture-Level Software Performance Models for Online Performance Prediction %U http://nbn-resolving.org/urn:nbn:de:swb:90-435372
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  Autonomic Performance-Aware Resource Management in Dynamic IT Service Infrastructures. Huber, Nikolaus; Thesis; Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany. (2014, July).
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  @phdthesis{Huber2014-KIT-AutonomicPerformanceAwareResourceManagement, author = {Huber, Nikolaus}, keywords = {Self-adaptive-systems}, month = {07}, school = {Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany}, title = {Autonomic Performance-Aware Resource Management in Dynamic IT Service Infrastructures}, year = 2014 }

  %0 Thesis %1 Huber2014-KIT-AutonomicPerformanceAwareResourceManagement %A Huber, Nikolaus %D 2014 %T Autonomic Performance-Aware Resource Management in Dynamic IT Service Infrastructures %U http://nbn-resolving.org/urn:nbn:de:swb:90-432462

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  Modelling Event-Based Interactions in Component-Based Architectures for Quantitative System Evaluation. Rathfelder, Christoph; Thesis; KIT Scientific Publishing. (2013).
  • [ BibTeX ]
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  @phdthesis{Rathfelder2013_1000032232, author = {Rathfelder, Christoph}, keywords = {descartes}, publisher = {{KIT Scientific Publishing}}, series = {The Karlsruhe Series on Software Design and Quality / Ed. by Prof. Dr. Ralf Reussner}, title = {Modelling Event-Based Interactions in Component-Based Architectures for Quantitative System Evaluation}, volume = 10, year = 2013 }

  %0 Thesis %1 Rathfelder2013_1000032232 %A Rathfelder, Christoph %B The Karlsruhe Series on Software Design and Quality / Ed. by Prof. Dr. Ralf Reussner %D 2013 %I KIT Scientific Publishing %T Modelling Event-Based Interactions in Component-Based Architectures for Quantitative System Evaluation %V 10

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  Performance Modeling and Benchmarking of Event-Based Systems. Sachs, Kai; Thesis; TU Darmstadt; Karolinenplatz 5, 64289 Darmstadt, Germany. (2010).
  • [ BibTeX ]
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  @phdthesis{KaiSachs-Thesis-2010, address = {Karolinenplatz 5, 64289 Darmstadt, Germany}, author = {Sachs, Kai}, keywords = {QPME_Bibliography}, school = {TU Darmstadt}, title = {Performance Modeling and Benchmarking of Event-Based Systems}, year = 2010 }

  %0 Thesis %1 KaiSachs-Thesis-2010 %A Sachs, Kai %C Karolinenplatz 5, 64289 Darmstadt, Germany %D 2010 %T Performance Modeling and Benchmarking of Event-Based Systems