Docker Mastery: Section 5 - Container Lifetime & Persistent Data

• 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

• Docker Mastery: with Kubernetes +Swarm from a Docker Captain

• GitHub: udemy-docker-mastery

• 講師的YouTube

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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:\>