阿葛廷

人一定要靠自己!

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  • section5-45, 46

    • Section Overview:
      • Defining the problem of persistent data
      • Key concepts with containers: immutable, ephemeral
      • Learning and using Data Volumes
      • Learning and using Bind Mounts
      • Assignments

Udemy

Container Lifetime & Persistent Data

  • Containers are ususlly immutable and ephemeral
  • “immutable infrastructure”: only re-deploy containers, never change
  • This is the ideal scenario, but what abhout databases, or unique data?
  • Docker gives us features to ensure these “separation of concerns”
  • This is known as “persistent data”
  • Two ways: Volumes and Bind Mounts
  • Volumes: make special location outsides of container UFS (union file system)
  • Bind Mounts: link container path to host path

Persisten Data: Volumes

  • VOLUME command in Dockerfile

  • cleanup unused volumes
    • docker volume prune

  • 看 volume 裝在哪

    • 下載 image

      • docker pull mysql

      • docker image inspect mysql

        •    ...
        "Volumes": {
        "/var/lib/mysql": {}
    },
    ...

    • Run Container

      • ` docker container run -d –name mysql –env MYSQL_ALLOW_EMPTY_PASSWORD=True mysql`

      • docker container inspect mysql

        •   ...
            
  "Mounts": [
            {
                "Type": "volume",
                "Name": "0d2f6a986f12e71d5f5b3e7e0263b839ae08c8b34e69c57d6f1fa2e6321e8562",
                "Source": "/var/lib/docker/volumes/0d2f6a986f12e71d5f5b3e7e0263b839ae08c8b34e69c57d6f1fa2e6321e8562/_data",
                "Destination": "/var/lib/mysql",
                "Driver": "local",
                "Mode": "",
                "RW": true,
                "Propagation": ""
            }
        ],
            
  ...
            
     "Volumes": {
            "/var/lib/mysql": {}
    },
              
  ...

  • 看 docker volume

    • docker volume ls

      •  PS E:\> docker volume ls
 DRIVER              VOLUME NAME
 local               0d2f6a986f12e71d5f5b3e7e0263b839ae08c8b34e69c57d6f1fa2e6321e8562

    • docker volume inspect <volume-name>

      •  PS E:\> docker volume inspect 0d2f6a986f12e71d5f5b3e7e0263b839ae08c8b34e69c57d6f1fa2e6321e8562
 [
     {
         "CreatedAt": "2020-01-02T08:16:58Z",
         "Driver": "local",
         "Labels": null,
         "Mountpoint": "/var/lib/docker/volumes/0d2f6a986f12e71d5f5b3e7e0263b839ae08c8b34e69c57d6f1fa2e6321e8562/_data",
         "Name": "0d2f6a986f12e71d5f5b3e7e0263b839ae08c8b34e69c57d6f1fa2e6321e8562",
         "Options": null,
         "Scope": "local"
     }
 ]

    • 如果你真的跑在 linux machine 可以找到實體檔案在:

      • "Mountpoint": "/var/lib/docker/volumes/0d2f6a986f12e71d5f5b3e7e0263b839ae08c8b34e69c57d6f1fa2e6321e8562/_data"

  • 看有趣的問題

    • 再 run 一個 mysql –name mysql2
    • 看 volume
      • 會有兩個
      • 而且誰是哪一個的不清楚! 
        •  PS E:\> docker volume ls
 DRIVER              VOLUME NAME
 local               0d2f6a986f12e71d5f5b3e7e0263b839ae08c8b34e69c57d6f1fa2e6321e8562
 local               be6c0139888d0c185ae26be507644270406ceeba633855725540e42444e1cca6
    • 停掉 兩個 containers
      • docker container stop mysql mysql2
      • volume 還在! 而且誰是哪一個的不清楚! 
        •  PS E:\> docker volume ls
 DRIVER              VOLUME NAME
 local               0d2f6a986f12e71d5f5b3e7e0263b839ae08c8b34e69c57d6f1fa2e6321e8562
 local               be6c0139888d0c185ae26be507644270406ceeba633855725540e42444e1cca6
    • 刪掉 兩個 containers
      • docker container rm mysql mysql2
      • volume 還在! 而且誰是哪一個的不清楚! 
        •  PS E:\> docker volume ls
 DRIVER              VOLUME NAME
 local               0d2f6a986f12e71d5f5b3e7e0263b839ae08c8b34e69c57d6f1fa2e6321e8562
 local               be6c0139888d0c185ae26be507644270406ceeba633855725540e42444e1cca6

Named Volume

  • -v : 兩種寫法

    • 寫法一: 有打沒打一樣，不會命名

      • -v /var/lib/mysql

    • 寫法二: 給名字! VolumeName:位置

      • -v <volume-name>:/var/lib/mysql

  • 檢查:

     PS E:\> docker container run -d --name mysql2 --env MYSQL_ALLOW_EMPTY_PASSWORD=True -v mysql-db:/var/lib/mysql mysql
 86a8b0c3a54db33c7a38f2fcd79314884dce5f13549b72f4c9a897f11115798d
 PS E:\> docker volume ls
 DRIVER              VOLUME NAME
 local               0d2f6a986f12e71d5f5b3e7e0263b839ae08c8b34e69c57d6f1fa2e6321e8562
 local               be6c0139888d0c185ae26be507644270406ceeba633855725540e42444e1cca6
 local               mysql-db
 PS E:\> docker volume inspect mysql-db
 [
     {
         "CreatedAt": "2020-01-02T08:46:19Z",
         "Driver": "local",
         "Labels": null,
         "Mountpoint": "/var/lib/docker/volumes/mysql-db/_data",
         "Name": "mysql-db",
         "Options": null,
         "Scope": "local"
     }
 ]

    • docker container inspect <container-name>

          PS E:\> docker container inspect mysql2
    ...
         "Mounts": [
             {
                 "Type": "volume",
                 "Name": "mysql-db",
                 "Source": "/var/lib/docker/volumes/mysql-db/_data",
                 "Destination": "/var/lib/mysql",
                 "Driver": "local",
                 "Mode": "z",
                 "RW": true,
                 "Propagation": ""
             }
         ],
     ...

Docker volume create

  • required to do this before “docker run” to use custom drivers and labels
PS E:\> docker volume create --help

Usage:  docker volume create [OPTIONS] [VOLUME]

Create a volume

Options:
  -d, --driver string   Specify volume driver name (default "local")
      --label list      Set metadata for a volume
  -o, --opt map         Set driver specific options (default map[])
PS E:\>

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