CRD-Shim: Declarative Container Runtime Orchestration via Kubernetes CRDs for Docker & containerd

• Jitendra Gupta

  Compunnel Inc.

  Author

Kubernetes is now an essential platform for orchestrating distributed containers based on a declarative API approach for deploying and managing containerized distributed applications. Conventionally, Kubernetes orchestration goes through intermediary layers like Pods, kubelet, and CRI, incurring extra latency, overhead, and complexity. This paper introduces CRD-Shim, a Kubernetes-native interface to directly orchestrate container runtimes like Docker and containerd declaratively using CRDs. CRD-Shim orchestrates runtimes by transforming Kubernetes CRDs into calls to their underlying native API calls without involving Pods, kubelet, and CRI. The architecture is compatible with container-specific resource objects and also provides high-level orchestration functionalities such as a controller for resource replication (ReplicaSet equivalent) purely through runtimes. Our experiment results show that CRD-Shim reduces the container startup and update latency to nearly 62% and 30%, respectively, compared with a single-node Kubernetes deployment, and decreases its runtime memory usage to almost 66% of that. CRD-Shim can serve as an effective option for scenarios where direct runtime management and low-latency orchestration are more critical than general container ecosystem management like edge computing, IoT and single-node systems.

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