docker storage volume

Data Volume

• Why data volumes (storage volumes) are needed

  • The docker image is made up of multiple read-only layers. When the container is started, the docker loads the read-only layer and adds a read-write layer to the mirror layer.

  • If the running container modifies an existing file, the file will be copied from the read-only layer below the read-write layer to the read-write layer. The read-only version of the file still exists, but has been hidden by a copy of the file in the read-write layer, which is the COW mechanism.
    

  • Close and restart the container without affecting its data, but delete the container and all its changes will be lost
  • Problems:
    • Storage and Federation file systems are not easily accessible by hosts
    • Container key data sharing is inconvenient
    • Deleting a container loses its data

volume

• What is a volume
  • Volumes are one or more directories on containers that bypass the federated file system and can be bound (associated) to a directory on the host machine.

Setting up random volumes

[root@centos7-node1 ~]# docker run --name mybbox5 -it -v /mydata --rm busybox /bin/sh     #Specify a container volume, which is automatically created if it does not exist
/ # cd /mydata/

[root@centos7-node1 ~]# docker inspect mybbox5   # Start another window to view mounts
  "Mounts": [
            {
                "Type": "volume",
                "Name": "a39b4a68fc51d83900093f35b05b4e29085b2d45d1fa9a19f63f75130dbf1d0c",
                "Source": "/data/docker/volumes/a39b4a68fc51d83900093f35b05b4e29085b2d45d1fa9a19f63f75130dbf1d0c/_data",
                "Destination": "/mydata",
                "Driver": "local",
                "Mode": "",
                "RW": true,
                "Propagation": ""
            }
        ],

Bind mounted volume

• Bind volumes from locally specified directories to containers
• Characteristic:
  • The local directory will not be deleted after the container is deleted, and the data is still there
  • Can exist without the life cycle of the container
  • With NFS storage, data can also exist natively
  • Sharing data between containers is possible

[root@centos7-node1 ~]# mkdir /data/volumes/v1 -p
[root@centos7-node1 v1]# echo "hello" > /data/volumes/v1/my.txt
[root@centos7-node1 ~]# docker run --name mybox -it -v /data/volumes/v1:/mydata busybox /bin/sh 
[root@centos7-node1 ~]# docker rm mybox
mybox
[root@centos7-node1 ~]# ls /data/volumes/v1/
my.txt

Cases of data sharing between containers

[root@centos7-node1 ~]# docker run --name box6 -it -d -v /data/volumes/v1:/mydata busybox /bin/sh 
[root@centos7-node1 ~]# docker run --name box7 -it --rm --volumes-from box6 busybox

inspect data display

[root@centos7-node1 v1]# docker inspect box7    #View containers to find corresponding fields
[root@centos7-node1 v1]# docker inspect -f {{.Mounts}} box6    #.Mounts is a top-level field
[root@centos7-node1 v1]# docker inspect -f {{.NetworkSettings.Networks.bridge}} box7     #Connection between multilevel fields

actual combat

• Containerized deployment of wordpress

  • php+http
  • nginx profile local storage
  • mysql
  • Web page data and mysql data stored locally
  • mysql needs to pass in-e mysql_at startupROOTPASSWORD=hello
• thinking
  • The three application containers are on the same network layer
  • Configuration files and data files need to be stored locally using bound volumes

[root@centos7-node1 ~]# mkdir /data/volumes/mysql
[root@centos7-node1 ~]# docker pull mysql:5.5
[root@centos7-node1 ~]# docker run --name db -d -v /data/volumes/mysql:/var/lib/mysql -e MYSQL_ROOT_PASSWORD=qwer1234 mysql:5.5
[root@centos7-node1 ~]# docker exec -it db /bin/bash      #Enter the database, create users and databases
root@38b54e3d76cf:/# mysql -uroot -p
mysql> create database wordpress charset utf8;
mysql> grant all on wordpress.* to 'wordpress'@'127.0.0.1' identified by 'wpss2020';

[root@centos7-node1 ~]# docker pull php:5.6-fpm
[root@centos7-node1 ~]# docker pull nginx:1.18-alpine 
[root@centos7-node1 ~]#mkdir /data/volumes/nginx_conf -p   #nginx profile directory
[root@centos7-node1 ~]# cat /data/volumes/nginx_conf/nginx_php.conf    #Define the Nginx-php configuration file
server {
    listen       80;
    server_name  localhost;

    location / {
        root   /www/wordpress;
        index  index.php;
    }

    error_page   500 502 503 504  /50x.html;
    location = /50x.html {
        root   /usr/share/nginx/html;
    }

    location ~ \.php$ {
        fastcgi_pass   php:9000;
        fastcgi_index  index.php;
        fastcgi_param  SCRIPT_FILENAME  /www/wordpress/$fastcgi_script_name;
        include        fastcgi_params;
    }
}
[root@centos7-node1 ~]# docker run --name php-fpm -d -v /data/volumes/web:/www  php:5.6-fpm    #Start php
[root@centos7-node1 ~]# docker run --name nginx_php -d -p 80:80 -v /data/volumes/nginx_conf:/etc/nginx/conf.d  --volumes-from php-fpm --link php-fpm:php nginx:1.18-alpine     #start nginx

[root@centos7-node1 ~]#  cd /data/volumes/web && wget https://wordpress.org/latest.zip
root@centos7-node1 web]# unzip wordpress-5.4.1.zip 
[root@centos7-node1 ~]# docker exec nginx_php nginx -s reload