One of the most common feature requested for the MySQL docker official image is adding replication master/slave ability. As docker-library/mysql#43 is closed by deciding that it's a feature should be implemented via init script, my example here is a demo of how to do it.

The official MySQL image have the customize ability by running script files under /docker-entrypoint-initdb.d/ directory. The script has to be either a shell script, .sh, or a SQL script, .sql or .sql.gz.

To implement the MySQL replication, I borrowed the code from PR: docker-library/mysql#43, modified and saved as replica.sh. As described in the script comments, we have 5 more special environment variables for replication.

• MYSQL_REPLICA_USER: create the given user on the intended master host
• MYSQL_REPLICA_PASS
• MYSQL_MASTER_SERVER: change master on this location on the intended slave
• MYSQL_MASTER_PORT: optional, by default 3306
• MYSQL_MASTER_WAIT_TIME: seconds to wait for the master to come up

The Dockerfile is very simple, just copied replica.sh to /docker-entrypoint-initdb.d/ directory. That's it.

Let's use the new MySQL image with replication ability. To do that, I created a simple docker-compose.yml file:

version: '2'
services:
    master:
        image: twang2218/mysql:5.7-replica
        build: .
        restart: unless-stopped
        ports:
            - 3306:3306
        environment:
            - MYSQL_ROOT_PASSWORD=master_passw0rd
            - MYSQL_REPLICA_USER=replica
            - MYSQL_REPLICA_PASS=replica_Passw0rd
        command: ["mysqld", "--log-bin=mysql-bin", "--server-id=1"]
    slave:
        image: twang2218/mysql:5.7-replica
        build: .
        restart: unless-stopped
        ports:
            - 3307:3306
        environment:
            - MYSQL_ROOT_PASSWORD=slave_passw0rd
            - MYSQL_REPLICA_USER=replica
            - MYSQL_REPLICA_PASS=replica_Passw0rd
            - MYSQL_MASTER_SERVER=master
            - MYSQL_MASTER_WAIT_TIME=10
        command: ["mysqld", "--log-bin=mysql-bin", "--server-id=2"]

Then, just simply run it by docker-compose up -d, then our MySQL replication master and slave are running. Feel free to create something on the master and check whether it's been replicated to the slave.

Added a new environment variable in the compoer file ：

• MYSQL_MASTER_PORT : Port for setting master

Command to add a auto-increment-offset parameter，set the self growth field to avoid conflict.

Other parameters are written in the optimised.cnf file ，Plus some optimized parameters of the mysqld, based on the 16G memory server. For reference only.

The mysql.sh script is based on the environment that has already been run on the MySQL master slave, will be the script copy / directory, waiting for the container to run it manually after the implementation of.

Tt like this docker exec -it master1_1 sh mysql.sh,then you can test the MySQL dual master. good luck !