TASK_89_Kubernetes_Sidecar_Containers.md

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Start:         2023-01-13 21:00:51
Finished:   2023-01-13 21:18:09

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• Requirements
• Steps
• Resources

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TASK 89: Kubernetes Sidecar Containers

Requirements

We have a web server container running the nginx image. The access and error logs generated by the web server are not critical enough to be placed on a persistent volume. However, Nautilus developers need access to the last 24 hours of logs so that they can trace issues and bugs. Therefore, we need to ship the access and error logs for the web server to a log-aggregation service.

Following the separation of concerns principle, we implement the Sidecar pattern by deploying a second container that ships the error and access logs from nginx. Nginx does one thing, and it does it well—serving web pages.

The second container also specializes in its task—shipping logs. Since containers are running on the same Pod, we can use a shared emptyDir volume to read and write logs.

• Create a pod named webserver.

• Create an emptyDir volume shared-logs.

• Create two containers from nginx and ubuntu images with latest tag only and remember to mention tag i.e nginx:latest,

• nginx container name should be nginx-container and ubuntu container name should be sidecar-container on webserver pod.

• Add command on sidecar-container:

  "sh","-c","while true; do cat /var/log/nginx/access.log /var/log/nginx/error.log; sleep 30; done"

• Mount the volume shared-logs on both containers at location /var/log/nginx, all containers should be up and running.

Note: The kubectl utility on jump_host has been configured to work with the kubernetes cluster.

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Steps

Create the manifest sidecar.yml for the resource definitions.

apiVersion: v1
kind: Pod
metadata:
  name: webserver
  labels:
    name: webserver
spec:
  volumes:
    - name: shared-logs
      emptyDir: {}
  containers:
    - name: nginx-container
      image: nginx:latest
      volumeMounts:
        - name: shared-logs
          mountPath: /var/log/nginx
    - name: sidecar-container
      image: ubuntu:latest
      command:
        [
          "sh",
          "-c",
          "while true; do cat /var/log/nginx/access.log /var/log/nginx/error.log; sleep 30; done",
        ]
      volumeMounts:
        - name: shared-logs
          mountPath: /var/log/nginx   

Apply.

kubectl apply -f sidecar.yml

Ensue the Pod is running.

$ kubectl get pods

NAME        READY   STATUS    RESTARTS   AGE
webserver   2/2     Running   0          39s 

To see if the container started successfully, we can check the Events that occured in the Pod.

$ kubectl describe pod webserver | grep Events -A 20
Events:
  Type    Reason     Age   From               Message
  ----    ------     ----  ----               -------
  Normal  Scheduled  119s  default-scheduler  Successfully assigned default/webserver to kodekloud-control-plane
  Normal  Pulling    118s  kubelet            Pulling image "nginx:latest"
  Normal  Pulled     105s  kubelet            Successfully pulled image "nginx:latest" in 12.651602268s
  Normal  Created    105s  kubelet            Created container nginx-container
  Normal  Started    105s  kubelet            Started container nginx-container
  Normal  Pulling    105s  kubelet            Pulling image "ubuntu:latest"
  Normal  Pulled     96s   kubelet            Successfully pulled image "ubuntu:latest" in 8.98893506s
  Normal  Created    95s   kubelet            Created container sidecar-container
  Normal  Started    94s   kubelet            Started container sidecar-container

We can also verify that the two logs are created by running a shell command on the Pod.

~$ kubectl exec -it webserver -- bash

Defaulting container name to nginx-container.
Use 'kubectl describe pod/webserver -n default' to see all of the containers in this pod.
root@webserver:/# 
root@webserver:/# ls -la /var/log/nginx
total 16
drwxrwxrwx 2 root root 4096 Jan 13 13:10 .
drwxr-xr-x 1 root root 4096 Jan 11 06:31 ..
-rw-r--r-- 1 root root    0 Jan 13 13:10 access.log
-rw-r--r-- 1 root root 2489 Jan 13 13:10 error.log

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Resources