Dockerizing Redmine

Migrate an existing Redmine application into a Docker based container. There are two main steps:

  1. Migrate MySQL database
  2. Migrate Redmine application

MySQL

Create an archive from the source data directory, where data to be migrated:

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$ sudo tar -C /var/lib/mysql -czf ~/mysql.tar.gz .

The directory /var/lib/mysql is the default location where all database related data are stored.

Download the archive:

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$ scp example.com:~/mysql.tar.gz .

Extract to the directory where we will map the host volume to the guest:

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$ sudo mkdir -p /srv/mysql && sudo tar -C $_ -xzf mysql.tar.gz

Download the latest (5.7.16 make sure it is the latest, because 8.x branch might not work) MySQL Docker image:

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$ docker pull mysql && docker pull mysql:5.7.16

Run a MySQL container with the data directory mounted from the host:

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$ docker run                         \
  --detach                           \
  --name mysql                       \
  --restart always                   \
  --volume /srv/mysql:/var/lib/mysql \
  mysql

Environment variables (MYSQL_ROOT_PASSWORD, MYSQL_DATABASE, MYSQL_USER, or MYSQL_PASSWORD) become unnecessary:

Do note that none of the variables below will have any effect if you start the container with a data directory that already contains a database: any pre-existing database will always be left untouched on container startup.[^1]

Now I should be able to access my existing database:

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$ docker exec -it mysql sh -c 'mysql -uredmine -p redmine'
Enter password:
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 5
Server version: 5.7.16 MySQL Community Server (GPL)
Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql>

But when accessing MySQL database from another host, we have to update the permissions. Let’s log into MySQL with root user:

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$ docker exec -it mysql sh -c 'mysql -uroot -p mysql'

Issue SQL commands:

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mysql> SELECT Host, User FROM db WHERE Db='redmine';
+-----------+---------+
| Host      | User    |
+-----------+---------+
| localhost | redmine |
+-----------+---------+
1 row in set (0.00 sec)
mysql> SELECT Host, User FROM user WHERE User='redmine';
+-----------+---------+
| host      | user    |
+-----------+---------+
| localhost | redmine |
+-----------+---------+
1 row in set (0.00 sec)

Only localhost is allowed for both the database and the user. This is problematic. How does one know the host of the container yet to be created? The easiest way is to allow access from all hosts:

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mysql> UPDATE db SET Host='%' WHERE Db='redmine';
Query OK, 1 row affected (0.01 sec)
Rows matched: 1  Changed: 1  Warnings: 0
mysql> UPDATE user SET Host='%' WHERE User='redmine';
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

We can restrict to a set of IP addresses such as 172.17.0.% or sub domains %.example.com. Docker networking uses 172.17.0.x range.

The better way is that when linking containers, should be able to update mysql container /etc/hosts file to include a redmine container field. Then, a wild card is not necessary.

But having to allow all hosts to connect is fine, because all hosts do not mean all hosts. The port is not bind or map to any open port in the host machine. Only the host (172.17.0.1) and other Docker containers inside the host can discover the service provided. Other machines or containers outside the host is not able to access at all.

Restart the container to have the update taking effect:

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$ docker restart mysql

Redmine

For a basic Redmine setup, there aren’t much to migrate, mainly just three directories, config, files, and log, others are application data. Configuration could be done via environment variables, and if logs weren’t important to migrate, we just need to move the files directory, which is used for file upload.