2.5.6.2 More Topics on Deploying MySQL Server with Docker

Note

Most of the following sample commands have container-registry.oracle.com/mysql/community-server as the Docker image being used (like with the docker pull and docker run commands); change that if your image is from another repository—for example, replace it with container-registry.oracle.com/mysql/enterprise-server for MySQL Enterprise Edition images downloaded from the Oracle Container Registry (OCR), or mysql/enterprise-server for MySQL Enterprise Edition images downloaded from My Oracle Support.

• The Optimized MySQL Installation for Docker

• Configuring the MySQL Server

• Persisting Data and Configuration Changes

• Running Additional Initialization Scripts

• Connect to MySQL from an Application in Another Docker Container

• Server Error Log

• Using MySQL Enterprise Backup with Docker

• Using mysqldump with Docker

• Known Issues

• Docker Environment Variables

The Optimized MySQL Installation for Docker

Docker images for MySQL are optimized for code size, which means they only include crucial components that are expected to be relevant for the majority of users who run MySQL instances in Docker containers. A MySQL Docker installation is different from a common, non-Docker installation in the following aspects:

• Only a limited number of binaries are included.

• All binaries are stripped; they contain no debug information.

Warning

Any software updates or installations users perform to the Docker container (including those for MySQL components) may conflict with the optimized MySQL installation created by the Docker image. Oracle does not provide support for MySQL products running in such an altered container, or a container created from an altered Docker image.

Configuring the MySQL Server

When you start the MySQL Docker container, you can pass configuration options to the server through the docker run command. For example:

docker run --name mysql1 -d container-registry.oracle.com/mysql/community-server:tag --character-set-server=utf8mb4 --collation-server=utf8mb4_col

The command starts the MySQL Server with utf8mb4 as the default character set and utf8mb4_col as the default collation for databases.

Another way to configure the MySQL Server is to prepare a configuration file and mount it at the location of the server configuration file inside the container. See Persisting Data and Configuration Changes for details.

Persisting Data and Configuration Changes

Docker containers are in principle ephemeral, and any data or configuration are expected to be lost if the container is deleted or corrupted (see discussions here). Docker volumes provides a mechanism to persist data created inside a Docker container. At its initialization, the MySQL Server container creates a Docker volume for the server data directory. The JSON output from the docker inspect command on the container includes a Mount key, whose value provides information on the data directory volume:

$> docker inspect mysql1
...
 "Mounts": [
            {
                "Type": "volume",
                "Name": "4f2d463cfc4bdd4baebcb098c97d7da3337195ed2c6572bc0b89f7e845d27652",
                "Source": "/var/lib/docker/volumes/4f2d463cfc4bdd4baebcb098c97d7da3337195ed2c6572bc0b89f7e845d27652/_data",
                "Destination": "/var/lib/mysql",
                "Driver": "local",
                "Mode": "",
                "RW": true,
                "Propagation": ""
            }
        ],
...

The output shows that the source directory /var/lib/docker/volumes/4f2d463cfc4bdd4baebcb098c97d7da3337195ed2c6572bc0b89f7e845d27652/_data, in which data is persisted on the host, has been mounted at /var/lib/mysql, the server data directory inside the container.

Another way to preserve data is to bind-mount a host directory using the --mount option when creating the container. The same technique can be used to persist the configuration of the server. The following command creates a MySQL Server container and bind-mounts both the data directory and the server configuration file:

docker run --name=mysql1 \
--mount type=bind,src=/path-on-host-machine/my.cnf,dst=/etc/my.cnf \
--mount type=bind,src=/path-on-host-machine/datadir,dst=/var/lib/mysql \
-d container-registry.oracle.com/mysql/community-server:tag

The command mounts path-on-host-machine/my.cnf at /etc/my.cnf (the server configuration file inside the container), and path-on-host-machine/datadir at /var/lib/mysql (the data directory inside the container). The following conditions must be met for the bind-mounting to work:

• The configuration file path-on-host-machine/my.cnf must already exist, and it must contain the specification for starting the server by the user mysql:

  [mysqld]
  user=mysql

  You can also include other server configuration options in the file.

• The data directory path-on-host-machine/datadir must already exist. For server initialization to happen, the directory must be empty. You can also mount a directory prepopulated with data and start the server with it; however, you must make sure you start the Docker container with the same configuration as the server that created the data, and any host files or directories required are mounted when starting the container.

Running Additional Initialization Scripts

If there are any .sh or .sql scripts you want to run on the database immediately after it has been created, you can put them into a host directory and then mount the directory at /docker-entrypoint-initdb.d/ inside the container. For example:

docker run --name=mysql1 \
--mount type=bind,src=/path-on-host-machine/scripts/,dst=/docker-entrypoint-initdb.d/ \
-d container-registry.oracle.com/mysql/community-server:tag

Connect to MySQL from an Application in Another Docker Container

By setting up a Docker network, you can allow multiple Docker containers to communicate with each other, so that a client application in another Docker container can access the MySQL Server in the server container. First, create a Docker network:

docker network create my-custom-net

Then, when you are creating and starting the server and the client containers, use the --network option to put them on network you created. For example:

docker run --name=mysql1 --network=my-custom-net -d container-registry.oracle.com/mysql/community-server

docker run --name=myapp1 --network=my-custom-net -d myapp

The myapp1 container can then connect to the mysql1 container with the mysql1 hostname and vice versa, as Docker automatically sets up a DNS for the given container names. In the following example, we run the mysql client from inside the myapp1 container to connect to host mysql1 in its own container:

docker exec -it myapp1 mysql --host=mysql1 --user=myuser --password

For other networking techniques for containers, see the Docker container networking section in the Docker Documentation.

Server Error Log

When the MySQL Server is first started with your server container, a server error log is NOT generated if either of the following conditions is true:

• A server configuration file from the host has been mounted, but the file does not contain the system variable log_error (see Persisting Data and Configuration Changes on bind-mounting a server configuration file).

• A server configuration file from the host has not been mounted, but the Docker environment variable MYSQL_LOG_CONSOLE is true (which is the variable's default state for MySQL 9.1 server containers). The MySQL Server's error log is then redirected to stderr, so that the error log goes into the Docker container's log and is viewable using the docker logs mysqld-container command.

To make MySQL Server generate an error log when either of the two conditions is true, use the --log-error option to configure the server to generate the error log at a specific location inside the container. To persist the error log, mount a host file at the location of the error log inside the container as explained in Persisting Data and Configuration Changes. However, you must make sure your MySQL Server inside its container has write access to the mounted host file.

Using MySQL Enterprise Backup with Docker

MySQL Enterprise Backup is a commercially-licensed backup utility for MySQL Server, available with MySQL Enterprise Edition. MySQL Enterprise Backup is included in the Docker installation of MySQL Enterprise Edition.

In the following example, we assume that you already have a MySQL Server running in a Docker container (see Section 2.5.6.1, “Basic Steps for MySQL Server Deployment with Docker” on how to start a MySQL Server instance with Docker). For MySQL Enterprise Backup to back up the MySQL Server, it must have access to the server's data directory. This can be achieved by, for example, bind-mounting a host directory on the data directory of the MySQL Server when you start the server:

docker run --name=mysqlserver \
--mount type=bind,src=/path-on-host-machine/datadir/,dst=/var/lib/mysql \
-d mysql/enterprise-server:9.1

With this command, the MySQL Server is started with a Docker image of the MySQL Enterprise Edition, and the host directory /path-on-host-machine/datadir/ has been mounted onto the server's data directory (/var/lib/mysql) inside the server container. We also assume that, after the server has been started, the required privileges have also been set up for MySQL Enterprise Backup to access the server (see Grant MySQL Privileges to Backup Administrator, for details). Use the following steps to back up and restore a MySQL Server instance.

To back up a MySQL Server instance running in a Docker container using MySQL Enterprise Backup with Docker, follow the steps listed here:

1. On the same host where the MySQL Server container is running, start another container with an image of MySQL Enterprise Edition to perform a back up with the MySQL Enterprise Backup command backup-to-image. Provide access to the server's data directory using the bind mount we created in the last step. Also, mount a host directory (/path-on-host-machine/backups/ in this example) onto the storage folder for backups in the container (/data/backups in the example) to persist the backups we are creating. Here is a sample command for this step, in which MySQL Enterprise Backup is started with a Docker image downloaded from My Oracle Support:

   $> docker run \
   --mount type=bind,src=/path-on-host-machine/datadir/,dst=/var/lib/mysql \
   --mount type=bind,src=/path-on-host-machine/backups/,dst=/data/backups \
   --rm mysql/enterprise-server:9.1 \
   mysqlbackup -umysqlbackup -ppassword --backup-dir=/tmp/backup-tmp --with-timestamp \
   --backup-image=/data/backups/db.mbi backup-to-image

   It is important to check the end of the output by mysqlbackup to make sure the backup has been completed successfully.

2. The container exits once the backup job is finished and, with the --rm option used to start it, it is removed after it exits. An image backup has been created, and can be found in the host directory mounted in the last step for storing backups, as shown here:

   $> ls /tmp/backups
   db.mbi

To restore a MySQL Server instance in a Docker container using MySQL Enterprise Backup with Docker, follow the steps listed here:

1. Stop the MySQL Server container, which also stops the MySQL Server running inside:

   docker stop mysqlserver

2. On the host, delete all contents in the bind mount for the MySQL Server data directory:

   rm -rf /path-on-host-machine/datadir/*

3. Start a container with an image of MySQL Enterprise Edition to perform the restore with the MySQL Enterprise Backup command copy-back-and-apply-log. Bind-mount the server's data directory and the storage folder for the backups, like what we did when we backed up the server:

   $> docker run \
   --mount type=bind,src=/path-on-host-machine/datadir/,dst=/var/lib/mysql \
   --mount type=bind,src=/path-on-host-machine/backups/,dst=/data/backups \
   --rm mysql/enterprise-server:9.1 \
   mysqlbackup --backup-dir=/tmp/backup-tmp --with-timestamp \
   --datadir=/var/lib/mysql --backup-image=/data/backups/db.mbi copy-back-and-apply-log
   
   mysqlbackup completed OK! with 3 warnings

   The container exits with the message " mysqlbackup completed OK!" once the backup job is finished and, with the --rm option used when starting it, it is removed after it exits.

4. Restart the server container, which also restarts the restored server, using the following command:

   docker restart mysqlserver

   Or, start a new MySQL Server on the restored data directory, as shown here:

   docker run --name=mysqlserver2 \
   --mount type=bind,src=/path-on-host-machine/datadir/,dst=/var/lib/mysql \
   -d mysql/enterprise-server:9.1

   Log on to the server to check that the server is running with the restored data.

Using mysqldump with Docker

Besides using MySQL Enterprise Backup to back up a MySQL Server running in a Docker container, you can perform a logical backup of your server by using the mysqldump utility, run inside a Docker container.

The following instructions assume that you already have a MySQL Server running in a Docker container and, when the container was first started, a host directory /path-on-host-machine/datadir/ has been mounted onto the server's data directory /var/lib/mysql (see bind-mounting a host directory on the data directory of the MySQL Server for details), which contains the Unix socket file by which mysqldump and mysql can connect to the server. We also assume that, after the server has been started, a user with the proper privileges (admin in this example) has been created, with which mysqldump can access the server. Use the following steps to back up and restore MySQL Server data:

Backing up MySQL Server data using mysqldump with Docker:

1. On the same host where the MySQL Server container is running, start another container with an image of MySQL Server to perform a backup with the mysqldump utility (see documentation of the utility for its functionality, options, and limitations). Provide access to the server's data directory by bind mounting /path-on-host-machine/datadir/. Also, mount a host directory (/path-on-host-machine/backups/ in this example) onto a storage folder for backups inside the container (/data/backups is used in this example) to persist the backups you are creating. Here is a sample command for backing up all databases on the server using this setup:

   $> docker run --entrypoint "/bin/sh" \ 
   --mount type=bind,src=/path-on-host-machine/datadir/,dst=/var/lib/mysql \
   --mount type=bind,src=/path-on-host-machine/backups/,dst=/data/backups \
   --rm container-registry.oracle.com/mysql/community-server:9.1 \
   -c "mysqldump -uadmin --password='password' --all-databases > /data/backups/all-databases.sql"

   In the command, the --entrypoint option is used so that the system shell is invoked after the container is started, and the -c option is used to specify the mysqldump command to be run in the shell, whose output is redirected to the file all-databases.sql in the backup directory.

2. The container exits once the backup job is finished and, with the --rm option used to start it, it is removed after it exits. A logical backup been created, and can be found in the host directory mounted for storing the backup, as shown here:

   $> ls /path-on-host-machine/backups/
   all-databases.sql

Restoring MySQL Server data using mysqldump with Docker:

1. Make sure you have a MySQL Server running in a container, onto which you want your backed-up data to be restored.

2. Start a container with an image of MySQL Server to perform the restore with a mysql client. Bind-mount the server's data directory, as well as the storage folder that contains your backup:

   $> docker run  \
   --mount type=bind,src=/path-on-host-machine/datadir/,dst=/var/lib/mysql \
   --mount type=bind,src=/path-on-host-machine/backups/,dst=/data/backups \
   --rm container-registry.oracle.com/mysql/community-server:9.1 \
   mysql -uadmin --password='password' -e "source /data/backups/all-databases.sql"

   The container exits once the backup job is finished and, with the --rm option used when starting it, it is removed after it exits.

3. Log on to the server to check that the restored data is now on the server.

Known Issues

• When using the server system variable audit_log_file to configure the audit log file name, use the loose option modifier with it; otherwise, Docker cannot start the server.

Docker Environment Variables

When you create a MySQL Server container, you can configure the MySQL instance by using the --env option (short form -e) and specifying one or more environment variables. No server initialization is performed if the mounted data directory is not empty, in which case setting any of these variables has no effect (see Persisting Data and Configuration Changes), and no existing contents of the directory, including server settings, are modified during container startup.

Environment variables which can be used to configure a MySQL instance are listed here:

• The boolean variables including MYSQL_RANDOM_ROOT_PASSWORD, MYSQL_ONETIME_PASSWORD, MYSQL_ALLOW_EMPTY_PASSWORD, and MYSQL_LOG_CONSOLE are made true by setting them with any strings of nonzero lengths. Therefore, setting them to, for example, “0”, “false”, or “no” does not make them false, but actually makes them true. This is a known issue.

• MYSQL_RANDOM_ROOT_PASSWORD: When this variable is true (which is its default state, unless MYSQL_ROOT_PASSWORD is set or MYSQL_ALLOW_EMPTY_PASSWORD is set to true), a random password for the server's root user is generated when the Docker container is started. The password is printed to stdout of the container and can be found by looking at the container’s log (see Starting a MySQL Server Instance).

• MYSQL_ONETIME_PASSWORD: When the variable is true (which is its default state, unless MYSQL_ROOT_PASSWORD is set or MYSQL_ALLOW_EMPTY_PASSWORD is set to true), the root user's password is set as expired and must be changed before MySQL can be used normally.

• MYSQL_DATABASE: This variable allows you to specify the name of a database to be created on image startup. If a user name and a password are supplied with MYSQL_USER and MYSQL_PASSWORD, the user is created and granted superuser access to this database (corresponding to GRANT ALL). The specified database is created by a CREATE DATABASE IF NOT EXIST statement, so that the variable has no effect if the database already exists.

• MYSQL_USER, MYSQL_PASSWORD: These variables are used in conjunction to create a user and set that user's password, and the user is granted superuser permissions for the database specified by the MYSQL_DATABASE variable. Both MYSQL_USER and MYSQL_PASSWORD are required for a user to be created—if any of the two variables is not set, the other is ignored. If both variables are set but MYSQL_DATABASE is not, the user is created without any privileges.

  Note

  There is no need to use this mechanism to create the root superuser, which is created by default with the password set by either one of the mechanisms discussed in the descriptions for MYSQL_ROOT_PASSWORD and MYSQL_RANDOM_ROOT_PASSWORD, unless MYSQL_ALLOW_EMPTY_PASSWORD is true.

• MYSQL_ROOT_HOST: By default, MySQL creates the 'root'@'localhost' account. This account can only be connected to from inside the container as described in Connecting to MySQL Server from within the Container. To allow root connections from other hosts, set this environment variable. For example, the value 172.17.0.1, which is the default Docker gateway IP, allows connections from the host machine that runs the container. The option accepts only one entry, but wildcards are allowed (for example, MYSQL_ROOT_HOST=172.*.*.* or MYSQL_ROOT_HOST=%).

• MYSQL_LOG_CONSOLE: When the variable is true (which is its default state for MySQL 9.1 server containers), the MySQL Server's error log is redirected to stderr, so that the error log goes into the Docker container's log and is viewable using the docker logs mysqld-container command.

  Note

  The variable has no effect if a server configuration file from the host has been mounted (see Persisting Data and Configuration Changes on bind-mounting a configuration file).

• MYSQL_ROOT_PASSWORD: This variable specifies a password that is set for the MySQL root account.

  Warning

  Setting the MySQL root user password on the command line is insecure. As an alternative to specifying the password explicitly, you can set the variable with a container file path for a password file, and then mount a file from your host that contains the password at the container file path. This is still not very secure, as the location of the password file is still exposed. It is preferable to use the default settings of MYSQL_RANDOM_ROOT_PASSWORD and MYSQL_ONETIME_PASSWORD both being true.

• MYSQL_ALLOW_EMPTY_PASSWORD. Set it to true to allow the container to be started with a blank password for the root user.

  Warning

  Setting this variable to true is insecure, because it is going to leave your MySQL instance completely unprotected, allowing anyone to gain complete superuser access. It is preferable to use the default settings of MYSQL_RANDOM_ROOT_PASSWORD and MYSQL_ONETIME_PASSWORD both being true.