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MySQL Docker image

This repository contains Dockerfiles for MySQL images for OpenShift. Users can choose between RHEL and CentOS based images.

Dockerfile for CentOS is called Dockerfile, Dockerfile for RHEL is called Dockerfile.rhel7.

Environment variables and volumes

The image recognizes the following environment variables that you can set during initialization by passing -e VAR=VALUE to the Docker run command.

Variable name Description
MYSQL_USER User name for MySQL account to be created
MYSQL_PASSWORD Password for the user account
MYSQL_DATABASE Database name
MYSQL_ROOT_PASSWORD Password for the root user (optional)

The following environment variables influence the MySQL configuration file. They are all optional.

Variable name Description Default
MYSQL_LOWER_CASE_TABLE_NAMES Sets how the table names are stored and compared 0
MYSQL_MAX_CONNECTIONS The maximum permitted number of simultaneous client connections 151
MYSQL_MAX_ALLOWED_PACKET The maximum size of one packet or any generated/intermediate string 200M
MYSQL_FT_MIN_WORD_LEN The minimum length of the word to be included in a FULLTEXT index 4
MYSQL_FT_MAX_WORD_LEN The maximum length of the word to be included in a FULLTEXT index 20
MYSQL_AIO Controls the innodb_use_native_aio setting value in case the native AIO is broken. See http://help.directadmin.com/item.php?id=529 1
MYSQL_TABLE_OPEN_CACHE The number of open tables for all threads 400
MYSQL_KEY_BUFFER_SIZE The size of the buffer used for index blocks 32M (or 10% of available memory)
MYSQL_SORT_BUFFER_SIZE The size of the buffer used for sorting 256K
MYSQL_READ_BUFFER_SIZE The size of the buffer used for a sequential scan 8M (or 5% of available memory)
MYSQL_INNODB_BUFFER_POOL_SIZE The size of the buffer pool where InnoDB caches table and index data 32M (or 50% of available memory)
MYSQL_INNODB_LOG_FILE_SIZE The size of each log file in a log group 8M (or 15% of available available)
MYSQL_INNODB_LOG_BUFFER_SIZE The size of the buffer that InnoDB uses to write to the log files on disk 8M (or 15% of available memory)
MYSQL_DEFAULTS_FILE Point to an alternative configuration file /etc/my.cnf
MYSQL_BINLOG_FORMAT Set sets the binlog format, supported values are row and statement statement
MYSQL_LOG_QUERIES_ENABLED To enable query logging set this to 1 0

You can also set the following mount points by passing the -v /host:/container flag to Docker.

Volume mount point Description
/var/lib/mysql/data MySQL data directory

Notice: When mouting a directory from the host into the container, ensure that the mounted directory has the appropriate permissions and that the owner and group of the directory matches the user UID or name which is running inside the container.

Usage

For this, we will assume that you are using the centos/mysql-56-centos7 image. If you want to set only the mandatory environment variables and not store the database in a host directory, execute the following command:

$ docker run -d --name mysql_database -e MYSQL_USER=user -e MYSQL_PASSWORD=pass -e MYSQL_DATABASE=db -p 3306:3306 centos/mysql-56-centos7

This will create a container named mysql_database running MySQL with database db and user with credentials user:pass. Port 3306 will be exposed and mapped to the host. If you want your database to be persistent across container executions, also add a -v /host/db/path:/var/lib/mysql/data argument. This will be the MySQL data directory.

If the database directory is not initialized, the entrypoint script will first run mysql_install_db and setup necessary database users and passwords. After the database is initialized, or if it was already present, mysqld is executed and will run as PID 1. You can stop the detached container by running docker stop mysql_database.

MySQL auto-tuning

When the MySQL image is run with the --memory parameter set and you didn't specify value for some parameters, their values will be automatically calculated based on the available memory.

Variable name Configuration parameter Relative value
MYSQL_KEY_BUFFER_SIZE key_buffer_size 10%
MYSQL_READ_BUFFER_SIZE read_buffer_size 5%
MYSQL_INNODB_BUFFER_POOL_SIZE innodb_buffer_pool_size 50%
MYSQL_INNODB_LOG_FILE_SIZE innodb_log_file_size 15%
MYSQL_INNODB_LOG_BUFFER_SIZE innodb_log_buffer_size 15%

MySQL root user

The root user has no password set by default, only allowing local connections. You can set it by setting the MYSQL_ROOT_PASSWORD environment variable. This will allow you to login to the root account remotely. Local connections will still not require a password.

To disable remote root access, simply unset MYSQL_ROOT_PASSWORD and restart the container.

Changing passwords

Since passwords are part of the image configuration, the only supported method to change passwords for the database user (MYSQL_USER) and root user is by changing the environment variables MYSQL_PASSWORD and MYSQL_ROOT_PASSWORD, respectively.

Changing database passwords through SQL statements or any way other than through the environment variables aforementioned will cause a mismatch between the values stored in the variables and the actual passwords. Whenever a database container starts it will reset the passwords to the values stored in the environment variables.

Default my.cnf file

With environment variables we are able to customize a lot of different parameters or configurations for the mysql bootstrap configurations. If you'd prefer to use your own configuration file, you can override the MYSQL_DEFAULTS_FILE env variable with the full path of the file you wish to use. For example, the default location is /etc/my.cnf but you can change it to /etc/mysql/my.cnf by setting MYSQL_DEFAULTS_FILE=/etc/mysql/my.cnf

Changing the replication binlog_format

Some applications may wish to use row binlog_formats (for example, those built with change-data-capture in mind). The default replication/binlog format is statement but to change it you can set the MYSQL_BINLOG_FORMAT environment variable. For example MYSQL_BINLOG_FORMAT=row. Now when you run the database with master replication turned on (ie, set the Docker/container cmd to be run-mysqld-master) the binlog will emit the actual data for the rows that change as opposed to the statements (ie, DML like insert...) that caused the change.