Docker container data management

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1. Data volumes of containers

1. What is a data volume?

One of the concepts of Docker is to package the application and the running environment, so the life cycle of docker container is usually the same as the program running in the container, and our requirement for data is persistence, and docker containers also need a channel to share data. These requirements led to the creation of docker data volumes.

Docker data volumes are directories specially designed to bypass federated file systems (UFS) and provide access to one or more containers.

Data volumes are designed to perpetuate data and are completely independent of the container’s life cycle. Therefore, Docker does not delete the data volumes attached to it when the container is deleted, nor does it have a similar garbage collection mechanism to process the data referenced by the container

2. Features of the data volume

Docker data volumes exist independently of docker and are separated from the lifetime of docker containers.
It exists in a docker host.
Docker data volume, can be directories, can also be files.
Docker container can use data volume technology to share data with host computer.

3. Features of the data volume

The data volume is initialized when the container is started. If the image used by the container contains data at the mount point, the data is copied to the newly initialized data volume.
Data volumes can be shared and reused between containers.
You can modify the contents of the data volume directly.
Data volume changes do not affect mirror updates.
The volume persists even if the container to which the data volume is mounted has been deleted.

4. Use the data volume

#Use the -v option to add data volumes to the container
docker run -v ~/container_data:/data -it IMAGE /bin/bash
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In the container


root@311b7376b879:/# ls  
bin  boot  data  dev  etc  home  lib  lib64  media  mnt  opt  proc  root  run  sbin  srv  sys  tmp  usr  var
root@311b7376b879:/# cd data/
root@311b7376b879:/data# echo "hi , what's up man ?" > hi.txt
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The host machine

huanchu-mbp:~ huanchu$ docker run -it -d -v ~/Documents/ttt:/data --name test1 nginx /bin/bash
huanchu-mbp:~ huanchu$ cat Documents/ttt/hi.txt 
hi , what's up man ?
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5. Add the access permission to the data volume

Mounted data has read and write permissions by default. However, you can also set the shared data mounted in the container to read-only, so that data modification can only be performed on the host machine, as follows:

#Ro: indicates read-only.
docker run -it -v ~/datavolume:/data:ro ubuntu /bin/bash
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6. Use Dockerfile to create a mirror containing the data volume

Dockerfile command: VOLUME ["/data"]Copy the code

Mount points created by VOLUME command in Dockerfile cannot specify the corresponding directory on the host and are automatically generated

Dockerfile

# Version: 0.0.1
FROM ubuntu:latest 
VOLUME ["/data/volume1","/data/volume2"]
RUN apt-get update RUN apt-get install -y nginx 
RUN echo 'Hi, I am in your container' > /usr/share/nginx/html/index.html
EXPOSE 80
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Build the mirror

docker build -t="mynginx2" .
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Start the container

docker run -it --name mynginx_test mynginx2
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Viewing data Volumes

root@e22ae166d8fa:/# ls
bin  boot  data  dev  etc  home  lib  lib64  media  mnt  opt  proc  root  run  sbin  srv  sys  tmp  usr  var
root@e22ae166d8fa:/# cd data/
root@e22ae166d8fa:/data# ls
volume1  volume2
root@e22ae166d8fa:/data# 
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View the host mount point

Docker inspect docker inspect docker inspect

You can see information for both mount points.

"Mounts": [
            {
                "Type": "volume",
                "Name": "596925f444bbcb7d3b75c3b844700ce8f43bd5fc8b18bb97f323e2825a1df13e",
                "Source": "/var/lib/docker/volumes/596925f444bbcb7d3b75c3b844700ce8f43bd5fc8b18bb97f323e2825a1df13e/_data",
                "Destination": "/data/volume1",
                "Driver": "local",
                "Mode": "",
                "RW": true,
                "Propagation": ""
            },
            {
                "Type": "volume",
                "Name": "0a28aed7c33a588dd74ce008d78670a5ff01dbea17e659597ebd5506bf8824cb",
                "Source": "/var/lib/docker/volumes/0a28aed7c33a588dd74ce008d78670a5ff01dbea17e659597ebd5506bf8824cb/_data",
                "Destination": "/data/volume2",
                "Driver": "local",
                "Mode": "",
                "RW": true,
                "Propagation": ""
            }
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Data volume container

1. What is a data volume container?

Named containers are used to attach data volumes to other containers for data sharing. Containers that attach data volumes are called data volume containers.

2. Create a data volume container

huanchu-mbp:Documents huanchu$ docker run -it -v ~/Documents/ttt:/data --name container_data ubuntu root@832301c940b6:/#  ls bin boot data dev etc home lib lib64 media mnt opt proc root run sbin srv sys tmp usr var root@832301c940b6:/# cd data/ root@832301c940b6:/data# ls Dockerfile com hi.txt root@832301c940b6:/data# echo Dockerfile com/ hi.txt root@832301c940b6:/data# echo Dockerfile com/ hi.txt root@832301c940b6:/data# echo "ha ha ha !" > ha.txt root@832301c940b6:/data# ls Dockerfile com ha.txt hi.txtCopy the code

3. Method of mounting a data volume container

docker run --volumes-from [container name]
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Create a new container and mount container_data, the data volume container you just created

huanchu-mbp:Documents huanchu$ docker run -it --name ubuntu_test --volumes-from container_data ubuntu /bin/bash
root@1d6b918c00e5:/# ls
bin  boot  data  dev  etc  home  lib  lib64  media  mnt  opt  proc  root  run  sbin  srv  sys  tmp  usr  var
root@1d6b918c00e5:/# cd data/
root@1d6b918c00e5:/data# ls
Dockerfile  com  ha.txt  hi.txt
root@1d6b918c00e5:/data# cat ha.txt 
ha ha ha !
root@1d6b918c00e5:/data# 
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Use the inspect command to view the mount details

"Mounts": [
            {
                "Type": "bind",
                "Source": "/Users/huanchu/Documents/ttt",
                "Destination": "/data",
                "Mode": "",
                "RW": true,
                "Propagation": "rprivate"
            }
        ]
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Data volume backup and restoration

Data volume data backup

methods

docker run --volumes-from [container name] -v $(pwd):/backup ubuntu tar cvf /backup/backup.tar
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For example,

docker run --volumes-from container_data -v ~/Documents/ttt:/backup --name ubuntu_test1 ubuntu tar cvf /backup/ubuntu_test1.tar /data

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You can view the backup data on the host

huanchu-mbp:ttt huanchu$ ls -l
total 1272
-rw-r--r--  1 huanchu  staff     191 12 24 15:48 Dockerfile
drwxr-xr-x  3 huanchu  staff      96 12 12 14:45 com
-rw-r--r--  1 huanchu  staff      11 12 24 17:04 ha.txt
-rw-r--r--  1 huanchu  staff      21 12 24 14:26 hi.txt
-rw-r--r--  1 huanchu  staff  593920 12 24 18:09 ubuntu_test1.tar
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Data volume data restoration