Personal blog of Yzmir Ramirez

Speakers:

Brent Compton
Director Storage Solution Architectures, Red Hat

Brent Compton is Director Storage Solution Architectures at Red Hat. He leads the team responsible for building Ceph and Gluster storage reference architectures with Red Hat Storage partners. Before Red Hat, Brent was responsible for emerging non-volatile memory software technologies at Fusion-io. Previous enterprise software leadership roles include VP Product Management at Micromuse (now IBM Tivoli Netcool) and Product Marketing Director within HP’s OpenView software division. Brent also served as Director Middleware Development Platforms at the LDS Church and as CIO at Joint Commission International. Brent has a tight-knit family, and can be found on skis or a mountain bike whenever possible.

Kyle Bader
Sr Solution Architect, Red Hat

Kyle Bader, a Red Hat senior architect, provides expertise in the design and operation of petabyte-scale storage systems using Ceph. He joined Red Hat as part of the 2014 Inktank acquisition. As a senior systems engineer at DreamHost, he helped implement, operate, and design Ceph and OpenStack-based systems for DreamCompute and DreamObjects cloud products.

Yves Trudeau
Principal Architect

Yves is a Principal Consultant at Percona, specializing in MySQL High-Availability and scaling solutions. Before joining Percona in 2009, he worked as a senior consultant for MySQL AB and Sun Microsystems, assisting customers across North America with NDB Cluster and Heartbeat/DRBD technologies. Yves holds a Ph.D. in Experimental Physics from Université de Sherbrooke. He lives in Québec, Canada with his wife and three daughters.

In this blog post, we’ll discuss some of the basics regarding Docker MySQL replication. Docker has gained widespread popularity in recent years as a lightweight alternative to virtualization. It is ideal for building virtual development and testing environments. The solution is flexible and seamlessly integrates with popular CI tools.

This post walks through the setup of MySQL replication with Docker using Percona Server 5.6 images. To keep things simple we’ll configure a pair of instances and override only the most important variables for replication. You can add whatever other variables you want to override in the configuration files for each instance.

Note: the configuration described here is suitable for development or testing. We’ve also used the operating system repository packages; for the latest version use the official Docker images. The steps described can be used to setup more slaves if required, as long as each slave has a different server-id.

First, install Docker and pull the Percona images (this will take some time and is only executed once):

# Docker install for Debian / Ubuntu
apt-get install docker.io
# Docker install for Red Hat / CentOS (requires EPEL repo)
yum install epel-release # If not installed already
yum install docker-io
# Pull docker repos
docker pull percona

Now create locally persisted directories for the:

1. Instance configuration
2. Data files

# Create local data directories
mkdir -p /opt/Docker/masterdb/data /opt/Docker/slavedb/data
# Create local my.cnf directories
mkdir -p /opt/Docker/masterdb/cnf /opt/Docker/slavedb/cnf
### Create configuration files for master and slave
vi /opt/Docker/masterdb/cnf/config-file.cnf
# Config Settings:
[mysqld]
server-id=1
binlog_format=ROW
log-bin
vi /opt/Docker/slavedb/cnf/config-file.cnf
# Config Settings:
[mysqld]
server-id=2

Great, now we’re ready start our instances and configure replication. Launch the master node, configure the replication user and get the initial replication co-ordinates:

# Launch master instance
docker run --name masterdb -v /opt/Docker/masterdb/cnf:/etc/mysql/conf.d -v /opt/Docker/masterdb/data:/var/lib/mysql -e MYSQL_ROOT_PASSWORD=mysecretpass -d percona:5.6
00a0231fb689d27afad2753e4350192bebc19ab4ff733c07da9c20ca4169759e
# Create replication user
docker exec -ti masterdb 'mysql' -uroot -pmysecretpass -vvv -e"GRANT REPLICATION SLAVE ON *.* TO repl@'%' IDENTIFIED BY 'slavepass'G"
mysql: [Warning] Using a password on the command line interface can be insecure.
--------------
GRANT REPLICATION SLAVE ON *.* TO repl@"%"
--------------
Query OK, 0 rows affected (0.02 sec)
Bye
### Get master status
docker exec -ti masterdb 'mysql' -uroot -pmysecretpass -e"SHOW MASTER STATUSG"
mysql: [Warning] Using a password on the command line interface can be insecure.
*************************** 1. row ***************************
             File: mysqld-bin.000004
         Position: 310
     Binlog_Do_DB:
 Binlog_Ignore_DB:
Executed_Gtid_Set:

If you look carefully at the “docker run” command for masterdb, you’ll notice we’ve defined two paths to share from local storage:

/opt/Docker/masterdb/data:/var/lib/mysql

• This maps the local “/opt/Docker/masterdb/data” to the masterdb’s container’s “/var/lib/mysql path”
• All files within the datadir “/var/lib/mysql” persist locally on the host running docker rather than in the container

/opt/Docker/masterdb/cnf:/etc/mysql/conf.d

• This maps the local “/opt/Docker/masterdb/cnf” directory to the container’s “/etc/mysql/conf.d” path
• The configuration files for the masterdb instance persist locally as well
• Remember these files augment or override the file in “/etc/mysql/my.cnf” within the container (i.e., defaults will be used for all other variables)

We’re done setting up the master, so let’s continue with the slave instance. For this instance the “docker run” command also includes the “–link masterdb:mysql” command, which links the slave instance to the master instance for replication.

After starting the instance, set the replication co-ordinates captured in the previous step:

docker run --name slavedb -d -v /opt/Docker/slavedb/cnf:/etc/mysql/conf.d -v /opt/Docker/slavedb/data:/var/lib/mysql --link masterdb:mysql -e MYSQL_ROOT_PASSWORD=mysecretpass -d percona:5.6
eb7141121300c104ccee0b2df018e33d4f7f10bf5d98445ed4a54e1316f41891
docker exec -ti slavedb 'mysql' -uroot -pmysecretpass -e'change master to master_host="mysql",master_user="repl",master_password="slavepass",master_log_file="mysqld-bin.000004",master_log_pos=310;"' -vvv
mysql: [Warning] Using a password on the command line interface can be insecure.
--------------
change master to master_host="mysql",master_user="repl",master_password="slavepass",master_log_file="mysqld-bin.000004",master_log_pos=310
--------------
Query OK, 0 rows affected, 2 warnings (0.23 sec)
Bye

Almost ready to go! The last step is to start replication and verify that replication running:

# Start replication
docker exec -ti slavedb 'mysql' -uroot -pmysecretpass -e"START SLAVE;" -vvv
mysql: [Warning] Using a password on the command line interface can be insecure.
--------------
START SLAVE
--------------
Query OK, 0 rows affected, 1 warning (0.00 sec)
Bye
# Verify replication is running OK
docker exec -ti slavedb 'mysql' -uroot -pmysecretpass -e"SHOW SLAVE STATUSG" -vvv
mysql: [Warning] Using a password on the command line interface can be insecure.
--------------
SHOW SLAVE STATUS
--------------
*************************** 1. row ***************************
               Slave_IO_State: Waiting for master to send event
                  Master_Host: mysql
                  Master_User: repl
                  Master_Port: 3306
                Connect_Retry: 60
              Master_Log_File: mysqld-bin.000004
          Read_Master_Log_Pos: 310
               Relay_Log_File: mysqld-relay-bin.000002
                Relay_Log_Pos: 284
        Relay_Master_Log_File: mysqld-bin.000004
             Slave_IO_Running: Yes
            Slave_SQL_Running: Yes
              Replicate_Do_DB:
          Replicate_Ignore_DB:
           Replicate_Do_Table:
       Replicate_Ignore_Table:
      Replicate_Wild_Do_Table:
  Replicate_Wild_Ignore_Table:
                   Last_Errno: 0
                   Last_Error:
                 Skip_Counter: 0
          Exec_Master_Log_Pos: 310
              Relay_Log_Space: 458
              Until_Condition: None
               Until_Log_File:
                Until_Log_Pos: 0
           Master_SSL_Allowed: No
           Master_SSL_CA_File:
           Master_SSL_CA_Path:
              Master_SSL_Cert:
            Master_SSL_Cipher:
               Master_SSL_Key:
        Seconds_Behind_Master: 0
Master_SSL_Verify_Server_Cert: No
                Last_IO_Errno: 0
                Last_IO_Error:
               Last_SQL_Errno: 0
               Last_SQL_Error:
  Replicate_Ignore_Server_Ids:
             Master_Server_Id: 1
                  Master_UUID: 230d005a-f1a6-11e5-b546-0242ac110004
             Master_Info_File: /var/lib/mysql/master.info
                    SQL_Delay: 0
          SQL_Remaining_Delay: NULL
      Slave_SQL_Running_State: Slave has read all relay log; waiting for the slave I/O thread to update it
           Master_Retry_Count: 86400
                  Master_Bind:
      Last_IO_Error_Timestamp:
     Last_SQL_Error_Timestamp:
               Master_SSL_Crl:
           Master_SSL_Crlpath:
           Retrieved_Gtid_Set:
            Executed_Gtid_Set:
                Auto_Position: 0
1 row in set (0.00 sec)
Bye

Finally, we have a pair of dockerized Percona Server 5.6 master-slave servers replicating!

As mentioned before, this is suitable for a development or testing environment. Before going into production with this configuration, think carefully about the tuning of the “my.cnf” variables and the choice of disks used for the data/binlog directories. It is important to remember that newer versions of Docker recommend using “networks” rather than “linking” for communication between containers.