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Flexible Migration in Blue-Green Deployments within a Fixed Cost

This paper presents the concept of PolyPod that consists of multiple Pods that run different versions of the same container image on the same node in order to share common libraries in memory. Its novelty is that it proposes a blueprint for blue-green deployments in order to balance maximum flexibility in the number of migration steps with maximum workload consolidation within a fixed total resource cost. This balance between flexibility and improved resource utilization is important for various application areas where users are served by the same application instance and have different time preferences for being upgraded to a new application version. The PolyPod concept is also relevant for a planned feature of Kubernetes so that Pods can be vertically scaled without re-starting them, but where scaling actions are aborted if the capacity of the node is to be exceeded. We explain how the PolyPod concept supports balancing flexible migration and resource utilization, with and without Pod restarts, by simulating various migration scenarios based on a quantitative cost model.