MongoDB Logrotate

MongoDB does not rotate it’s log on it’s own.

To get it to ratet we will use logrotate.

First, we need to configure some things in mongod.conf to get the desired behaviour when we utilize logrotate.

systemLog:
 destination: file
 path: /var/log/mongodb/mongod.log
 logAppend: true
 logRotate: reopen

Afterwards, we can create a logroatet configuration going in /etc/logrotate.d/mongodb.

/var/log/mongodb/mongod.log
{
 rotate 5 # Keep the last 5 rotated logs, so 6 files including the currently active
 size 10M # Rotate once the log reaches 10MB in size, depending on your envrionment you could instead use daily, weekly, monthly, etc
 missingok # It's ok if the log file does not exist
 create 0600 mongodb mongodb # Permissions and ownership for the roatetd logs
 delaycompress # Don't compress on first rotation, so we have the current log and log.1 uncompressed
 compress  # Compress everything else
 sharedscripts # Run this script only once and not for every matching file
 postrotate # Script to run after rotating
 /bin/kill -SIGUSR1 $(systemctl show --property MainPID --value mongod.service)
 endscript # End of script
}

The postrotate script simply finds the PID of mongod.service: systemctl show --property MainPID --value mongod.service and sends it a SIGUSR1 which is the signal MongoDB expects if you wish to rotate the log.

Finally, test the configuration by running

ls -la /var/log/mongodb/
sudo logrotate --force /etc/logrotate.d/mongodb
ls -la /var/log/mongodb/

For quick reference this Ansible task can be used to provision this logrotate configuration, simply place it locally in files/logrotate-mongodb and include it in your play.

- name: Provision MongoDB logrotate configuration
 copy:
 src: "logrotate-mongod"
 dest: "/etc/logrotate.d/mongodb"
 owner: "root"
 mode: "644"
 force: true
 become: true