Sidecars

You can add sidecar containers to your job by specifying them under the sidecars key of the kubernetes plugin. These containers are started at the same time as the job's command containers. However, there is no guarantee that your sidecar containers will have started before the commands in your job's command containers are executed. Therefore, using retries or a tool like wait-for-it is recommended to avoid failed dependencies in the event that the sidecar container is still in the process of getting started.

Sidecar container differences

The sidecar containers configured by the Agent Stack for Kubernetes controller differ from sidecar containers defined by Kubernetes. True Kubernetes sidecar containers run as init containers, whereas sidecar containers defined by the controller run as application containers in the Pod alongside the job's command containers.

The following pipeline example shows how to use an nginx container as a sidecar container and run curl from the job's command container to interact with the nginx container:

steps:
  - label: "<img class="emoji" title="kubernetes" alt=":k8s:" src="https://buildkiteassets.com/emojis/img-buildkite-64/kubernetes.png" draggable="false" /> Use nginx sidecar"
    agents:
      queue: "kubernetes"
    plugins:
      - kubernetes:
          sidecars:
            - image: nginx:latest
          podSpec:
            containers:
              - image: curlimages/curl:latest
                name: curl
                command:
                  - curl --retry 10 --retry-all-errors localhost:80

For example, you can use sidecar containers to run asynchronous commands against files or directories or both under the /workspace directory outside of the command containers:

steps:
  - label: "<img class="emoji" title="kubernetes" alt=":k8s:" src="https://buildkiteassets.com/emojis/img-buildkite-64/kubernetes.png" draggable="false" /> Write file to extraVolumeMount on sidecar containers"
    agents:
      queue: "kubernetes"
    plugins:
      - kubernetes:
          sidecars:
            - image: alpine:latest
              command: ["sh"]
              args:
                - "-c"
                - |-
                  touch /workspace/pass-the-parcel
                  ls -lah /workspace/pass-the-parcel
          podSpec:
            containers:
              - image: alpine:latest
                command:
                  - |-
                    COUNT=0
                    until [[ $$((COUNT++)) == 15 ]]; do
                      [[ -f "/workspace/pass-the-parcel" ]] && break
                      echo "⚠️   Waiting for my package to be to be downloaded..."
                      sleep 1
                    done

                    if ! [[ -f "/workspace/pass-the-parcel" ]]; then
                      echo "⛔ My package has not been downloaded!"
                      exit 1
                    fi

                    echo "✅ My package has been downloaded!"
                    rm -f "/workspace/pass-the-parcel"