[CKA] KodeKloud - Multi Container PODs

 

 

안녕하세요, 쯀리입니다.

오늘은Multi Container PODs에 대해 알아보겠습니다. 
보통 하나의 파드에 하나의 컨테이너가 실행되는 것이 대다수인데 여러개의 컨테이너를 하나의 Pod에 배포하는것에 대해 알아볼게요.

https://kubernetes.io/docs/tasks/access-application-cluster/communicate-containers-same-pod-shared-volume/

Communicate Between Containers in the Same Pod Using a Shared Volume

 

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Multi-Container Pods

Kubernetes에서 Multi-Container Pods는 하나의 Pod 안에 여러 개의 컨테이너를 포함하는 것을 의미합니다. Pod는 Kubernetes에서 가장 작은 배포 단위로, 하나 이상의 컨테이너를 포함할 수 있습니다. Multi-Container Pod는 여러 컨테이너가 서로 밀접하게 협력하며 동작해야 할 때 유용합니다.

Multi-Container Pod의 사용 사례

1. Sidecar 패턴: 주 컨테이너의 기능을 보조하기 위해 보조 컨테이너를 사용하는 패턴입니다. 예를 들어, 로깅, 데이터 수집, 프록시 등의 역할을 할 수 있습니다.
2. Ambassador 패턴: 주 컨테이너를 대신하여 네트워크 요청을 처리하는 역할을 합니다.
3. Adapter 패턴: 주 컨테이너의 출력을 다른 형식으로 변환하는 역할을 합니다.

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Quiz

1. Identify the number of containers created in the red pod.

controlplane ~ ➜  k describe pod red
Name:             red
....
Containers:
  apple:
    Container ID:  
    Image:         busybox
    Image ID:      
    Port:          <none>
    Host Port:     <none>
    Command:
      sleep
      4500
    State:          Waiting
      Reason:       ContainerCreating
    Ready:          False
    Restart Count:  0
    Environment:    <none>
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from kube-api-access-npq8n (ro)
  wine:
    Container ID:  
    Image:         busybox
    Image ID:      
    Port:          <none>
    Host Port:     <none>
    Command:
      sleep
      4500
    State:          Waiting
      Reason:       ContainerCreating
    Ready:          False
    Restart Count:  0
    Environment:    <none>
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from kube-api-access-npq8n (ro)
  scarlet:
    Container ID:  
    Image:         busybox
    Image ID:      
    Port:          <none>
    Host Port:     <none>
    Command:
      sleep
      4500
    State:          Waiting
      Reason:       ContainerCreating
    Ready:          False
    Restart Count:  0
    Environment:    <none>
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from kube-api-access-npq8n (ro)

apple, wine, scarlet 이렇게 3개가 있네요

2. Identify the name of the containers running in the blue pod.

Containers:
  teal:
    Container ID:  containerd://b7bc24496e9b0c0e5237d28eee4a1cc58c885ea76b8a6f4215e0fe7bb347415c
    Image:         busybox
    Image ID:      docker.io/library/busybox@sha256:9ae97d36d26566ff84e8893c64a6dc4fe8ca6d1144bf5b87b2b85a32def253c7
    Port:          <none>
    Host Port:     <none>
    Command:
      sleep
      4500
    ....
  navy:
    Container ID:  containerd://bc7321a7573f03e3ce16c164d73082b4c7e4d7715d6906c4fba04f42ca8a5317
    Image:         busybox
    Image ID:      docker.io/library/busybox@sha256:9ae97d36d26566ff84e8893c64a6dc4fe8ca6d1144bf5b87b2b85a32def253c7
    Port:          <none>
    Host Port:     <none>
    Command:
      sleep
      4500
    ...

배포되어있는 컨테이너는 teal & navy 입니다.

3. Create a multi-container pod with 2 containers.
Use the spec given below:
If the pod goes into the crashloopbackoff then add the command sleep 1000 in the lemon container.

Name: yellow
Container 1 Name: lemon
Container 1 Image: busybox
Container 2 Name: gold
Container 2 Image: redis

controlplane ~ ➜  cat multi-con.yaml 
apiVersion: v1
kind: Pod
metadata:
  name: yellow
spec:
  restartPolicy: Never
  containers:

  - name: lemon
    image: busybox
    command: 
      - "sleep"
      - "1000"

  - name: gold
    image: redis

 

5. We have deployed an application logging stack in the elastic-stack namespace. Inspect it.

controlplane ~ ➜  k get pods -n elastic-stack
NAME             READY   STATUS    RESTARTS   AGE
app              1/1     Running   0          11m
elastic-search   1/1     Running   0          11m
kibana           1/1     Running   0          11m

 

6. Once the pod is in a ready state, inspect the Kibana UI using the link above your terminal. There shouldn't be any logs for now. We will configure a sidecar container for the application to send logs to Elastic Search.
You can inspect the Kibana logs by running:

 

kubectl -n elastic-stack logs kibana

 

7. Inspect the app pod and identify the number of containers in it.
It is deployed in the elastic-stack namespace.

controlplane ~ ✖ k describe po app -n elastic-stack
Name:             app
Namespace:        elastic-stack
Priority:         0
Service Account:  default
Node:             controlplane/192.35.64.6
Start Time:       Thu, 04 Jul 2024 15:34:19 +0000
Labels:           name=app
Annotations:      <none>
Status:           Running
IP:               10.244.0.4
IPs:
  IP:  10.244.0.4
Containers:
  app:
    Container ID:   containerd://123485ad14b8e2a217633724e2ee4240694bff47fc81bc6cb123f5722e1e15f9
    Image:          kodekloud/event-simulator
    Image ID:       docker.io/kodekloud/event-simulator@sha256:1e3e9c72136bbc76c96dd98f29c04f298c3ae241c7d44e2bf70bcc209b030bf9
    Port:           <none>
    Host Port:      <none>
  ....

1개 

8. The application outputs logs to the file /log/app.log. View the logs and try to identify the user having issues with Login. Inspect the log file inside the pod.

controlplane ~ ➜  k exec -it app -n elastic-stack -c app -- cat /log/app.log | grep Login
[2024-07-04 15:34:30,019] WARNING in event-simulator: USER5 Failed to Login as the account is locked due to MANY FAILED ATTEMPTS.
[2024-07-04 15:34:35,025] WARNING in event-simulator: USER5 Failed to Login as the account is locked due to MANY FAILED ATTEMPTS.

User5이 문제입니다!

9. Edit the pod in the elastic-stack namespace to add a sidecar container to send logs to Elastic Search. Mount the log volume to the sidecar container.

https://kubernetes.io/docs/tasks/access-application-cluster/communicate-containers-same-pod-shared-volume/

Communicate Between Containers in the Same Pod Using a Shared Volume

Only add a new container. Do not modify anything else. Use the spec provided below.

Name: app
Container Name: sidecar
Container Image: kodekloud/filebeat-configured
Volume Mount: log-volume
Mount Path: /var/log/event-simulator/
Existing Container Name: app
Existing Container Image: kodekloud/event-simulator

 

---
apiVersion: v1
kind: Pod
metadata:
  name: app
  namespace: elastic-stack
  labels:
    name: app
spec:
  containers:
  - name: app
    image: kodekloud/event-simulator
    volumeMounts:
    - mountPath: /log
      name: log-volume

  - name: sidecar
    image: kodekloud/filebeat-configured
    volumeMounts:
    - mountPath: /var/log/event-simulator/
      name: log-volume

  volumes:
  - name: log-volume
    hostPath:
      # directory location on host
      path: /var/log/webapp
      # this field is optional
      type: DirectoryOrCreate

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하나의 파드에 하나의 컨테이너에 대한 것만 익히다가 다중 컨테이너 사용을 보니 새롭습니다. 

Multi-Container Pod의 특징

1. 단일 네트워크 네임스페이스: 동일한 Pod 내의 모든 컨테이너는 같은 네트워크 네임스페이스를 공유하므로, localhost로 서로 통신할 수 있습니다.
2. 공유 볼륨: 같은 Pod 내의 컨테이너는 동일한 볼륨을 마운트하여 데이터를 공유할 수 있습니다.
3. 공동 스케줄링: Pod의 모든 컨테이너는 동일한 노드에 배치되며, 같이 스케줄링됩니다.

다음시간에는 init Containers에 관해 알아보겠습니다. 

 

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참조

※ Udemy Labs - Certified Kubernetes Administrator with Practice Tests