A Blog of the ZHAW Zurich University of Applied Sciences
The “Dependability Modeling Framework” (DMF) becomes famous: Konstantin Benz and Thomas M. Bohnert will present their newest paper about the Dependability Modeling Framework at the First International Workshop on “Cloud Technologies and Energy Efficiency in Mobile Communication Network” (CLEEN) which takes place from September 2-5 in Las Vegas. The ICCLab researchers will show a methodology on […]
In part 3 of our article series “Dependability Modeling on OpenStack” we have discussed that we should run Chaos Monkey tests on an OpenStack HA installation and then collect data about the impact of the attack. While we did say that we want to collect data about the implemented OpenStack HA architecture, we were not […]
In this part of the Dependability Modeling article series we explain how a test framework on an OpenStack architecture can be established. The test procedure has 4 steps: in a first step, we implement the OpenStack environment following the planned system architecture. In the second step we calculate the probabilities of component outages during a given timeframe (e. g. 1 year). Then we start a Chaos Monkey script which “attacks” (randomly disables) the components of the system environment using the calculated probabilities as a base for the attack. As a last step we measure the impact of the Chaos Monkey attack according to the table of failure impact sizes we created in part 2. The impact of the attack should be stored as dataset in a database. Steps 1-4 form one test run. Multiple test runs can be performed on multiple architectures to create a empirical data which allows us to rate the different OpenStack architectures according to their availability.
In the previous article we defined use cases for an OpenStack implementation according to the usage scenario in which the OpenStack environment is deployed. In this part of the Dependability Modeling article series we will show how these use cases relate to functions and services provided by the OpenStack environment and create a set of dependabilities between use cases, functions, services and system components. From this set we will draw the dependency graph and make the impact of component outages computable.
Dependability Modeling is carried out in 4 steps: model the user intercations, model the system functions, model the system services and then model the system components which make system services available. In the first part we will define which interactions could be expected from end users of the OpenStack cloud platform and construct the first part of the dependability graph. Once the dependapility model is constructed, a Dependability Analysis will be performed and several OpenStack HA architectures will be rated according to their outage risk.
In a former article we spoke about testing High Availability in OpenStack with the Chaos Monkey. While the Chaos Monkey is a great tool to test what happens if some system components fail, it does not reveal anything about the general strengths and weaknesses of different system architectures. In order to determine if an architecture with 2 redundant controller nodes and 2 compute nodes offers a higher availability level than an architecture with 3 compute nodes and only 1 controller node, a framework for testing different architectures is required. The “Dependability Modeling Framework” seems to be a great opportunity to evaluate different system architectures on their ability to achieve availability levels required by end users.