title: Model checking for cloud autoscaling using WATERS

authors: van Zijl, Martin

subjects: cloud computing

abstract: This thesis investigates the use of formal methods to verify cloud system designs against Service Level Agreements (SLAs), towards providing guarantees under uncertainty. We used WATERS (the Waikato Analysis Toolkit for Events in Reactive Systems), which is a model-checking tool based on discrete event systems. We created models for one aspect of cloud computing, horizontal autoscaling, and used this to verify cloud system designs against an SLA that specifies the maximum request response time.

To evaluate the accuracy of the WATERS models, the cloud system designs are simulated on a private Kubernetes cluster, using JMeter to drive the workload. The results from Kubernetes are compared to the verification results from WATERS. A key research goal was to have these match as closely as possible, and to explain the discrepancies between the two. This process is followed for two applications: a default installation of NGINX, a web server with a fast but variable response time, and a hand-written Node.js program enforcing a fixed response time.

The results suggest that WATERS can be used to predict potential SLA violations. Lessons learned include that the state space must be constrained to avoid excessive checking times, and we provide a method for doing so. An advantage of our model checking-based technique is that it verifies against all possible patterns of arriving requests (up to a given maximum), which would be impractical to test with a load testing tool such as JMeter.

A key difference from existing work is our use non-probabilistic finite state machines, as opposed to probabilistic models which are prevalent in existing research. In addition, we have attempted to model the detail of the autoscaling process (a “white-box” approach), whereas much existing research attempts to find patterns between autoscaling parameters and SLA violation, effectively viewing autoscaling as a black-box process.

Future work includes refining the WATERS models to more closely match Kubernetes, and modelling other SLO types. Other methods may also be used to limit the compilation and verification time for the models. This includes attempting different algorithms and perhaps editing the models to reduce the state space.

text: Model checking for cloud autoscaling using WATERS This thesis investigates the use of formal methods to verify cloud system designs against Service Level Agreements (SLAs), towards providing guarantees under uncertainty. We used WATERS (the Waikato Analysis Toolkit for Events in Reactive Systems), which is a model-checking tool based on discrete event systems. We created models for one aspect of cloud computing, horizontal autoscaling, and used this to verify cloud system designs against an SLA that specifies the maximum request response time.

To evaluate the accuracy of the WATERS models, the cloud system designs are simulated on a private Kubernetes cluster, using JMeter to drive the workload. The results from Kubernetes are compared to the verification results from WATERS. A key research goal was to have these match as closely as possible, and to explain the discrepancies between the two. This process is followed for two applications: a default installation of NGINX, a web server with a fast but variable response time, and a hand-written Node.js program enforcing a fixed response time.

The results suggest that WATERS can be used to predict potential SLA violations. Lessons learned include that the state space must be constrained to avoid excessive checking times, and we provide a method for doing so. An advantage of our model checking-based technique is that it verifies against all possible patterns of arriving requests (up to a given maximum), which would be impractical to test with a load testing tool such as JMeter.

A key difference from existing work is our use non-probabilistic finite state machines, as opposed to probabilistic models which are prevalent in existing research. In addition, we have attempted to model the detail of the autoscaling process (a “white-box” approach), whereas much existing research attempts to find patterns between autoscaling parameters and SLA violation, effectively viewing autoscaling as a black-box process.

Future work includes refining the WATERS models to more closely match Kubernetes, and modelling other SLO types. Other methods may also be used to limit the compilation and verification time for the models. This includes attempting different algorithms and perhaps editing the models to reduce the state space.

year: 2020

title: Ethical issues in organizational practices: individuals, organizations and partnerships

authors: Wang, Ying

subjects: Business ethics

abstract: This thesis examines issues regarding ethics in organizational practices. It explores ethics-related inquiries from the influences of an individual’s moral character and conduct, to an organization’s pursuit of a higher value system, and to organizations’ social and ethical practices in the broader context of cross-sector collaborations. The thesis comprises four research papers, with topics ranging from ethics and value-based motivations, issues surrounding ethical governance, to the evolving process of organizational value systems. It asks specific questions such as what are the motivating factors that drive ethical practice, how to effectively govern organizational conduct, and how organizations across spheres can best mobilize their efforts in aligning with evolving social and ethical values. In examining current practices as well as their implied philosophies, the thesis seeks to contribute to the field of business ethics, both in its theoretical engagement with the theory of ‘virtue ethics’, and by gaining insight into the various factors that help foster individuals’ as well as organizations’ ethical and moral development. Overall, the thesis highlights the need for a greater ethical dimension in organizational practices, whether it is individually oriented commitment, or an organization’s collective goals of value creation, both in the mix of motivations that drive ethical practice and in developing ethics-based governance mechanisms, towards an overarching pursuit of a higher value system with greater moral and ethical aspirations.

text: Ethical issues in organizational practices: individuals, organizations and partnerships This thesis examines issues regarding ethics in organizational practices. It explores ethics-related inquiries from the influences of an individual’s moral character and conduct, to an organization’s pursuit of a higher value system, and to organizations’ social and ethical practices in the broader context of cross-sector collaborations. The thesis comprises four research papers, with topics ranging from ethics and value-based motivations, issues surrounding ethical governance, to the evolving process of organizational value systems. It asks specific questions such as what are the motivating factors that drive ethical practice, how to effectively govern organizational conduct, and how organizations across spheres can best mobilize their efforts in aligning with evolving social and ethical values. In examining current practices as well as their implied philosophies, the thesis seeks to contribute to the field of business ethics, both in its theoretical engagement with the theory of ‘virtue ethics’, and by gaining insight into the various factors that help foster individuals’ as well as organizations’ ethical and moral development. Overall, the thesis highlights the need for a greater ethical dimension in organizational practices, whether it is individually oriented commitment, or an organization’s collective goals of value creation, both in the mix of motivations that drive ethical practice and in developing ethics-based governance mechanisms, towards an overarching pursuit of a higher value system with greater moral and ethical aspirations.

year: 2020

title: Are they really at risk? Students' stories of success.

authors: Gray, Sheridan

subjects: Student engagement

abstract: In 2011, as the year level dean for year 13, I was surprised and pleased to see a group of students complete their fifth year of secondary schooling, contrary to teacher expectations, and in spite of earlier signs of disengagement and struggle.  Such students are frequently labelled “at risk” in our secondary schools. Truancy, lack of achievement, conduct issues, learning difficulties and health problems are seen as indicators of an at risk student by teachers. 

Statistically in Aotearoa, Māori and Pasifika students and students from low socio-economic families tend to be overrepresented among disengaged or early leavers from secondary schools, and so being from these cultures, and being from a low socio-economic group becomes a “risk” factor.   This can lead to assumptions among teachers about the students’ families, how parents value education, and even about the capacity of these groups to be able to succeed in education.  A range of strategies and programmes have been implemented in an attempt to address these issues, including Te Kotahitanga, Ka Hikitia and the Pasifika Education Plan, Resource Teachers Learning and Behaviour, Restorative Practice, and more recently Positive Behaviour for Learning

While there has been a shift in such approaches from deficit of students to emphasising more positive attitudes in teachers, the perspectives of the students themselves are missing from the discussion about these issues.  This study asks students what factors helped them to stay, and to achieve at least a level one NCEA qualification

The findings show that retention and engagement of “at risk” students requires careful attention to the quality of relationships across the school community: students, teachers and parents. They discredit some commonly held assumptions that “at risk” students and their parents do not value education and that teachers cannot support these students sufficiently. These quality relationships are respectful, responsive and tenacious showing a high level of respect for and interest in the students that goes beyond a teaching and learning relationship.  It also suggests that the discourse of “risk” invites a disrespectful response to retention and engagement of students.

text: Are they really at risk? Students' stories of success. In 2011, as the year level dean for year 13, I was surprised and pleased to see a group of students complete their fifth year of secondary schooling, contrary to teacher expectations, and in spite of earlier signs of disengagement and struggle.  Such students are frequently labelled “at risk” in our secondary schools. Truancy, lack of achievement, conduct issues, learning difficulties and health problems are seen as indicators of an at risk student by teachers. 

Statistically in Aotearoa, Māori and Pasifika students and students from low socio-economic families tend to be overrepresented among disengaged or early leavers from secondary schools, and so being from these cultures, and being from a low socio-economic group becomes a “risk” factor.   This can lead to assumptions among teachers about the students’ families, how parents value education, and even about the capacity of these groups to be able to succeed in education.  A range of strategies and programmes have been implemented in an attempt to address these issues, including Te Kotahitanga, Ka Hikitia and the Pasifika Education Plan, Resource Teachers Learning and Behaviour, Restorative Practice, and more recently Positive Behaviour for Learning

While there has been a shift in such approaches from deficit of students to emphasising more positive attitudes in teachers, the perspectives of the students themselves are missing from the discussion about these issues.  This study asks students what factors helped them to stay, and to achieve at least a level one NCEA qualification

The findings show that retention and engagement of “at risk” students requires careful attention to the quality of relationships across the school community: students, teachers and parents. They discredit some commonly held assumptions that “at risk” students and their parents do not value education and that teachers cannot support these students sufficiently. These quality relationships are respectful, responsive and tenacious showing a high level of respect for and interest in the students that goes beyond a teaching and learning relationship.  It also suggests that the discourse of “risk” invites a disrespectful response to retention and engagement of students.

year: 2012