How can I enable MySQL binary logging using the official Docker image? - mysql

Question

What would be the best way to enable binary logging using the official mysql image?
I have tried using the mysql:5.7 image, overriding the command when running it to also pass through the startup options to enable binary logging to mysqld (see below). The problem with this approach is that the mysql user does not have permission to write to the /var/log/mysql directory.
The run command:
docker run -d \
--name mysql \
-v /var/lib/mysql:/var/lib/mysql \
mysql:5.7 \
mysqld \
--datadir=/var/lib/mysql \
--user=mysql \
--server-id=1 \
--log-bin=/var/log/mysql/mysql-bin.log \
--binlog_do_db=test
The output:
mysqld: File '/var/log/mysql/mysql-bin.index' not found (Errcode: 2 - No such file or directory)
Should I fork the repository and add a volume for /var/log/mysql which the mysql user can write to and create a custom image, or is there a better way to do it? Is this possible using only the official mysql image?

Answer 1

The problem with this approach is that the mysql user does not have permission to write to the /var/log/mysql directory
The problem actually is that the directory /var/log/mysql does not exists on the mysql:5.7 Docker image. You can make sure of it running the following container:
$ docker run --rm mysql:5.7 ls /var/log/
alternatives.log
apt
bootstrap.log
btmp
dmesg
dpkg.log
faillog
fsck
lastlog
wtmp
Furthermore, MySQL binary logs aren't logs meant for following your MySQL server activity or errors ; they are logs meant to give your MySQL server a chance to recover data in case of a server crash.
As a consequence, you want those binary logs:
to stay close to your data
to be written on a fast file system
In most cases, Docker container file system is slow and that's why the MySQL data folder for the container is declared as a VOLUME.
So you also want your binary logs to be written on a Docker data volume and not the Docker container file system.
long story short, start your container with:
docker run -d \
--name mysql \
-v /var/lib/mysql:/var/lib/mysql \
mysql:5.7 \
mysqld \
--datadir=/var/lib/mysql \
--user=mysql \
--server-id=1 \
--log-bin=/var/lib/mysql/mysql-bin.log \
--binlog_do_db=test