Oh My Iron man post - day three

Posted on 2019-09-04 Edited on 2022-03-07 In IT鐵人賽 Views: Disqus:

Oh My Logs ! 談談如何在K8s中收集logs - 3

目錄
- Introduce and analysis
- Cluster level ELK
- 💎Sidecar mode 💎
- Integrate log collecting component into an app

HI 大家今天過得好嗎？
今天要來動手做個sidecar

以下這張來自官網的圖很清楚地解釋了sidecar on K8s的運作模式
![](https://i.imgur.com/uSzyGDi.png =350x350)

大部分的pod只運行一個container, 但在某些情況下
我們必須要在一個pod運行兩個以上的containers, 這種multi-container的模式又可以衍伸至三種design patterns:

sidecar pattern: 最簡單的方式，兩個container利用volume的方式share同一個檔案目錄
adapter pattern: 利用另外一個container做接口，把要輸出的資料格式化，例如同一套log system便可以處理不同pods的log
ambassador pattern: 假若開發環境是在local, 此種模式可以將pod要輸出的資料直接寫在local的資料庫等

此圖出自這裡, 這張圖蠻清楚的描述了三種模式的不同，但由於篇幅以及時間關係，我就先講sidecar mode

這邊就利用上面文件裡的範例寫一個帶有nginx sidecar的pod yaml.

apiVersion: v1
kind: Pod
metadata:
  name: pod-with-sidecar
spec:
  # Create a volume called 'shared-logs' that the
  # app and sidecar share.
  volumes:
  - name: shared-logs 
    emptyDir: {}

  # In the sidecar pattern, there is a main application
  # container and a sidecar container.
  containers:

  # Main application container
  - name: app-container
    # Simple application: write the current date
    # to the log file every five seconds
    image: alpine # alpine is a simple Linux OS image
    command: ["/bin/sh"]
    args: ["-c", "while true; do date >> /var/log/app.txt; sleep 5;done"]

    # Mount the pod's shared log file into the app 
    # container. The app writes logs here.
    volumeMounts:
    - name: shared-logs
      mountPath: /var/log

  # Sidecar container
  - name: sidecar-container
    # Simple sidecar: display log files using nginx.
    # In reality, this sidecar would be a custom image
    # that uploads logs to a third-party or storage service.
    image: nginx:1.7.9
    ports:
      - containerPort: 80

    # Mount the pod's shared log file into the sidecar
    # container. In this case, nginx will serve the files
    # in this directory.
    volumeMounts:
    - name: shared-logs
      mountPath: /usr/share/nginx/html # nginx-specific mount path