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Version: 1.0.0

PodSpec Customization

PodSpec Customization refers to the process of specifying and configuring the attributes and settings of a pod in Kubernetes through its PodSpec.

A PodSpec defines the characteristics of a pod, including the containers it contains, the volumes it uses, the networking settings, resource requests and limits, environment variables, and more.

PodSpec Customization in Zeet​

You can provide custom YAML to be applied to the PodSpec in the Kubernetes tab of your project settings.

Example: Specifying Instance Type​

An example use case would be to specify the particular instance type you want for your pods. To do so, you can apply the following patch:

nodeSelector:
  aws.instance-type: m5.large

Note that changing your instance type might require us to provision a new node pool for your pod. This might result in some downtime for your service.

Example: Extract container information as envvar​

It is sometimes useful for containers to have information about itself such as the podIP, nodeName, or hostIP. An example use case for pod-spec customization would be to extract this information for your container as an environment variable. To do so, you can apply the following patch:

containers:
  - name: container
    env:
      - name: HOST_IP
        valueFrom:
          fieldRef:
            fieldPath: status.hostIP

This example extracts the hostIP as an environment variable. But you can follow this example to expose any of the available fields via the Kubernetes Downward API.

Entrypoint and Command in Docker and Kubernetes​

Docker​

  • Entrypoint: The ENTRYPOINT in a Dockerfile specifies the default application to be run when a container is started. It's the primary command the Docker container is built to run.
  • Command: The CMD in a Dockerfile provides default arguments to the ENTRYPOINT. These arguments can be overridden when the container is run.

Kubernetes​

  • Command: In Kubernetes, command overrides the default ENTRYPOINT of the Docker container.
  • Args: In Kubernetes, args overrides the default CMD specified in the Docker container.

In summary, in Docker, ENTRYPOINT sets the executable to be called when the container runs, and CMD sets default arguments for the ENTRYPOINT. In Kubernetes, command and args correspond to Docker's ENTRYPOINT and CMD, respectively.

Example: Customizing Entrypoint in Zeet​

In Zeet, to customize the PodSpec for the Docker entrypoint, you can use the KubernetesCustomizationInput.podSpecPatch as a workaround. You can inject your desired entrypoint like this:

containers:
  - name: container
    command: ["/new-entrypoint.sh"]
    args: ["arg1", "arg2"]

This YAML snippet sets a new entrypoint /new-entrypoint.sh and arguments for the container in your Kubernetes pod.