Container Compute Service:Ignore the NotReady state of the sidecar container

Introduction

ACS clusters do not support DaemonSets due to the limits of virtual nodes. To achieve a DaemonSet-like effect, you can add sidecar containers to pods in ACS clusters. After you add a sidecar container, if the status of the sidecar container is NotReady, the status of the pod is NotReady.

In some scenarios, you may not want the status of the sidecar container to affect the status of the entire pod. For example, you may want to use a sidecar container to collect logs. If the logging container encounters an issue, the application containers need to continue providing external services.

To address the issue, ACS provides the feature to ignore the NotReady status of a container. If you do not want the status of a container to affect the status of the entire pod, you can add an environment variable to ignore the status of the container. After you add the environment variable, the pod can still enter the Ready state when the container is in the NotReady state.

How to configure

The environment variable that is used to ignore the status of a container is __IGNORE_READY__. A value of true specifies that the status of the container is ignored.

Examples

1. Write a YAML configuration file for the application, and then use the YAML file to create a Deployment.

   kubectl apply -f test-ignore.yaml

   In the following example, a YAML file named test-ignore.yaml is provided to create a Deployment that contains one pod replica. The pod contains two containers. The app container runs as normal. The sidecar container returns a non-zero status code and cannot enter the Ready state.

   apiVersion: apps/v1
   kind: Deployment
   metadata:
     name: test-ignore
     labels:
       app: test
   spec:
     replicas: 1 
     selector:
       matchLabels:
         app: test
     template:
       metadata:
         labels:
           app: test
       spec:
         containers:
         - name: app
           image: registry-cn-hangzhou.ack.aliyuncs.com/ack-demo/busybox:1.28
           command: ["/bin/sh", "-c", "sleep 999"] 
         - name: sidecar
           image: registry-cn-hangzhou.ack.aliyuncs.com/ack-demo/busybox:1.28
           command: ["/bin/sh", "-c", "exit 1"] 
           env:
           - name: __IGNORE_READY__
             value: "true"

2. View the details of the pod and check the status of the pod.

   kubectk get pod <pod-name> -o yaml

   Expected results:

   ...
   status:
     conditions:
       - lastTransitionTime: '2024-08-02T09:36:14Z'
         status: 'True'
         type: Initialized
       - lastTransitionTime: '2024-08-02T09:36:16Z'
         status: 'True'
         type: Ready
       - lastTransitionTime: '2024-08-02T09:36:16Z'
         status: 'True'
         type: ContainersReady
       - lastTransitionTime: '2024-08-02T09:36:15Z'
         status: 'True'
         type: PodScheduled
       - lastTransitionTime: '2024-08-02T09:36:14Z'
         status: 'True'
         type: ContainerHasSufficientDisk
   ...

   In the response, check the Ready and ContainersReady parameters in the status.conditions section. The status values of the parameters are True, which indicates that the NotReady state of the sidecar container is ignored.