Elastic Container Instance:Forcibly terminate the sidecar container and ignore the container exit code

Feature description

If you use Elastic Container Instance in Container Service for Kubernetes (ACK) Serverless clusters, Elastic Container Instance does not support the DaemonSet feature of Kubernetes due to the limitation of virtual nodes. In some scenarios where you want to use DaemonSets, you can add sidecar containers to Elastic Container Instance-based pods to achieve a similar effect as DaemonSets. However, if you set the RestartPolicy parameter to OnFailure or Never, the lifecycle of the pods is affected. For example, after you add a filebeat sidecar container to a job, the sidecar container continues to run after application containers exit. As a result, the job cannot reach the desired state and cannot complete running.

For the preceding scenarios, Elastic Container Instance supports the following features:

• Specify the type of containers

  You can use environment variables to add a type label to a sidecar container. This way, if application containers exit and do not restart, Elastic Container Instance forcibly terminates the running of the sidecar container to ensure that the job can complete running.

• Ignore the exit codes of containers

  If Elastic Container Instance forcibly terminates the running of the sidecar container, the exit code of the sidecar container is not 0 to indicate that the container terminates in the failed state. Then, the final state of the job is Failed. To address this issue, you can use environment variables of containers to ignore the exit code of the sidecar container and forcibly set the state of sidecar container to Succeeded. This ensures that the final state of the job is Succeeded.

Configuration description

Configuration example

1. Write the YAML configuration file of a job and then use the YAML file to create the job.

   kubectl apply -f test-sidecar.yaml

   The following example provides a YAML file named test-sidecar.yaml. In the file, a job that includes two containers is created. c1 is the application container, and c2 is the sidecar container. Environment variables are added to specify the type of containers and ignore the exit codes of containers.

   apiVersion: batch/v1
   kind: Job
   metadata:
     name: test
   spec:
     template:
       metadata:
         labels:
           app: test
           alibabacloud.com/eci: "true" 
       spec:
         containers:
         - name: c1
           image: registry.cn-shanghai.aliyuncs.com/eci_open/perl:5
           command: ["perl","-Mbignum=bpi","-wle","print bpi(2000)"]
         - name: c2
           image: registry.cn-shanghai.aliyuncs.com/eci_open/perl:5
           command: ["/bin/sh","-c","sleep 999"] 
           env:
           - name: ECI_CONTAINER_TYPE
             value: "sidecar"
           - name: ECI_CONTAINER_IGNORE_EXIT_CODE
             value: "true"
         restartPolicy: Never
         backoffLimit: 2

2. View the details of the job and pod and observe the effect of the environment variables.

   • Run the following command to check whether the final state of the job is Succeeded.

     kubectl describe job <job-name>

     Sample response:

     

   • View the details of the sidecar container and check the actual exit code and related information.

     kubectl describe pod <pod-name>

     Sample response: