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MySQL 5.6 Reference Manual  /  ...  /  More Topics on Deploying MySQL Server with Docker

2.5.8.2 More Topics on Deploying MySQL Server with Docker

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:

  • Included binaries are limited to:

    • /usr/bin/my_print_defaults

    • /usr/bin/mysql

    • /usr/bin/mysql_config

    • /usr/bin/mysql_install_db

    • /usr/bin/mysql_tzinfo_to_sql

    • /usr/bin/mysql_upgrade

    • /usr/bin/mysqladmin

    • /usr/bin/mysqlcheck

    • /usr/bin/mysqldump

    • /usr/sbin/mysqld

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

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, for the MySQL Server:

docker run --name mysql1 -d mysql/mysql-server --character-set-server=utf8mb4 --collation-server=utf8mb4_col

The command starts your MySQL Server with utf8mb4 as the default character set and utf8mb4_col as the default collation for your 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, however, 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 for running the docker inspect command on the container has a Mount key, whose value provides information on the data directory volume:

shell> 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 folder /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 mysql/mysql-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 using 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, for a MySQL Server container:

docker run --name=mysql1 \
--mount type=bind,src=/path-on-host-machine/scripts/,dst=/docker-entrypoint-initdb.d/ \
-d mysql/mysql-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 mysql/mysql-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 (the variable's default state for MySQL 5.6 server containers is false). 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.

Docker Environment Variables

When you create a MySQL Server container, you can configure the MySQL instance by using the --env option (-e in short) and specifying one or more of the following environment variables.

Notes
  • None of the variables below has any effect if the data directory you mount is not empty, as no server initialization is going to be attempted then (see Persisting Data and Configuration Changes for more details). Any pre-existing contents in the folder, including any old server settings, are not modified during the container startup.

  • 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 non-zero 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 of the MySQL Server containers.

  • MYSQL_RANDOM_ROOT_PASSWORD: When this variable is true (which is its default state, unless MYSQL_ROOT_PASSWORD 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 (the variable's default state for MySQL 5.6 server containers is false), 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=true and MYSQL_ONETIME_PASSWORD=true being both 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=true and MYSQL_ONETIME_PASSWORD=true being both true.


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