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: The ecology of the lucerne flea, Sminthurus viridis, in the South-Auckland/Waikato area

authors: Dentener, Peter Roeland

abstract: Lucerne flea, Sminthurus viridis L., is an annual pest in pastures in the Auckland/Waikato area. It damages legumes, particularly white clover, from late autumn until early summer, with a peak in infestation in spring. No research into the seasonality of the lucerne flea (LF) has been done in New Zealand. It was therefore decided to study the bionomics and population dynamics of LF, and aspects related to the damage, caused by LF.

The study showed that the life cycle of LF consisted of three nymphal instars, one adult male and three adult female instars with the males being smaller and lighter in weight than the females. The population of LF built up steadily from March or April onwards to reach a peak in numbers in October or November after which the numbers declined to a low level and LF were only present as diapause eggs. Rainfall in March and April played an important role in the hatching of the diapause eggs and influenced the survival of the first instar larvae. The accumulated temperature (°D) above a zero development threshold of 4 °C determined the number of generations of LF per year, with five generations in 1982 and four in 1983 in Huntly. Shutting up a paddock for hay production as well as the consecutive cutting of the hay influenced the number of LF in the field. Population dynamic studies of LF showed that LF populations had overlapping stages of development as well as overlapping generations during the study period.  Examination of the data with methods, equivalent to the k-factor analysis, showed that LF populations were prone to great changes in number at the beginning of the immature stage of the life cycle of the males and the end of the life cycle of the females, but fairly stable at the time that sexual maturity was reached. The locomotory activity of LF took place during the day and night and all growth stages were active. No statistically significant relationship could be found between the locomotory activity and temperature or rainfall. The mite, Bdellodes lapidaria, a predator of LF, was found in the study sites in Huntly but their numbers were so low that no control effect on LF could be established. Feeding trials showed that adult female LF ate significantly more than adult male LF, and that the feeding rate was highest at 15 and 20 °C and a photophase of 12 and 16 hours light. Other results suggested that some feeding activity would also occur at night. Severe damage by LF in the field reduced the leaf surface area of white clover plants by up to 40 % during this study, and most severe damage was observed in October and November. Observations in the field and the laboratory established that LF is a wasteful feeder.

text: The ecology of the lucerne flea, Sminthurus viridis, in the South-Auckland/Waikato area Lucerne flea, Sminthurus viridis L., is an annual pest in pastures in the Auckland/Waikato area. It damages legumes, particularly white clover, from late autumn until early summer, with a peak in infestation in spring. No research into the seasonality of the lucerne flea (LF) has been done in New Zealand. It was therefore decided to study the bionomics and population dynamics of LF, and aspects related to the damage, caused by LF.

The study showed that the life cycle of LF consisted of three nymphal instars, one adult male and three adult female instars with the males being smaller and lighter in weight than the females. The population of LF built up steadily from March or April onwards to reach a peak in numbers in October or November after which the numbers declined to a low level and LF were only present as diapause eggs. Rainfall in March and April played an important role in the hatching of the diapause eggs and influenced the survival of the first instar larvae. The accumulated temperature (°D) above a zero development threshold of 4 °C determined the number of generations of LF per year, with five generations in 1982 and four in 1983 in Huntly. Shutting up a paddock for hay production as well as the consecutive cutting of the hay influenced the number of LF in the field. Population dynamic studies of LF showed that LF populations had overlapping stages of development as well as overlapping generations during the study period.  Examination of the data with methods, equivalent to the k-factor analysis, showed that LF populations were prone to great changes in number at the beginning of the immature stage of the life cycle of the males and the end of the life cycle of the females, but fairly stable at the time that sexual maturity was reached. The locomotory activity of LF took place during the day and night and all growth stages were active. No statistically significant relationship could be found between the locomotory activity and temperature or rainfall. The mite, Bdellodes lapidaria, a predator of LF, was found in the study sites in Huntly but their numbers were so low that no control effect on LF could be established. Feeding trials showed that adult female LF ate significantly more than adult male LF, and that the feeding rate was highest at 15 and 20 °C and a photophase of 12 and 16 hours light. Other results suggested that some feeding activity would also occur at night. Severe damage by LF in the field reduced the leaf surface area of white clover plants by up to 40 % during this study, and most severe damage was observed in October and November. Observations in the field and the laboratory established that LF is a wasteful feeder.

year: 1985

title: Talking About Race and Positionality in Psychology: Asians as Tangata Tiriti

authors: Tan, Kyle K. H.

subjects: tangata whenua

abstract: The article discusses the dominance of Western, educated, industrialized, rich, and democratic (WEIRD) perspectives in the field of psychology in Aotearoa New Zealand. This has resulted in a racial hierarchy of knowledge, with Indigenous and culturally diverse epistemologies marginalized. The lack of diversity in the curriculum and the limited representation of non-Pākehā (non-New Zealand European) psychologists in the country have led to calls for a more inclusive environment.

The first perspective proposed is to understand Asians as a racialized group with diverse experiences. Asians in Aotearoa come from various backgrounds and face different degrees of racism and acculturation. The notion of 'Asian' may be used to marginalize the interests of Māori, perpetuating institutional racism. The concept of 'Asianisations' describes different forms of racial marginalization experienced by Asians in the country.

The second perspective emphasizes the positionality of Asians as tangata Tiriti (people of the Treaty). Te Tiriti o Waitangi, the Treaty between the British Crown and Māori chiefs, is seen as granting tangata Tiriti equal rights and privileges alongside Pākehā and Māori. As tangata Tiriti, Asians have a responsibility to uphold Tiriti principles, which include partnership, active protection, equity, and options to address Māori inequities. Asian psychologists can engage in culturally safe care for Māori clients and collaborate with and empower Māori leadership in research.

The article highlights the need for Asian psychologists to reflect on their positionality, power structures, and biases within the discipline and society. It encourages them to challenge the dominance of WEIRD psychology and work towards decolonizing the field. By doing so, they can contribute to the flourishing of Kaupapa Māori psychology and develop culturally informed practices that draw on the richness of Asian cultures.

text: Talking About Race and Positionality in Psychology: Asians as Tangata Tiriti The article discusses the dominance of Western, educated, industrialized, rich, and democratic (WEIRD) perspectives in the field of psychology in Aotearoa New Zealand. This has resulted in a racial hierarchy of knowledge, with Indigenous and culturally diverse epistemologies marginalized. The lack of diversity in the curriculum and the limited representation of non-Pākehā (non-New Zealand European) psychologists in the country have led to calls for a more inclusive environment.

The first perspective proposed is to understand Asians as a racialized group with diverse experiences. Asians in Aotearoa come from various backgrounds and face different degrees of racism and acculturation. The notion of 'Asian' may be used to marginalize the interests of Māori, perpetuating institutional racism. The concept of 'Asianisations' describes different forms of racial marginalization experienced by Asians in the country.

The second perspective emphasizes the positionality of Asians as tangata Tiriti (people of the Treaty). Te Tiriti o Waitangi, the Treaty between the British Crown and Māori chiefs, is seen as granting tangata Tiriti equal rights and privileges alongside Pākehā and Māori. As tangata Tiriti, Asians have a responsibility to uphold Tiriti principles, which include partnership, active protection, equity, and options to address Māori inequities. Asian psychologists can engage in culturally safe care for Māori clients and collaborate with and empower Māori leadership in research.

The article highlights the need for Asian psychologists to reflect on their positionality, power structures, and biases within the discipline and society. It encourages them to challenge the dominance of WEIRD psychology and work towards decolonizing the field. By doing so, they can contribute to the flourishing of Kaupapa Māori psychology and develop culturally informed practices that draw on the richness of Asian cultures.

year: 2023-07-24