MongoDB Log Rotation Automation

When you are using mongodb for large applications (heavy write and read intensive), then you probable noticed that mongod.log/mongos.log file is growing big in size with in a few time span. I saw 20GB mongos.log file size in a single day. So, your logfile should be in a limited size for diagnostics and debugging purpose. Other wise if some error happens and you want to take quick analysis of those logfile, then probably it will be very cumbersome job. To serve this purpose we need log file should be rotate with reference of either by time or by size.

Below are the few points you can do as per the mongodb documentation in your mongod.conf file.

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

You have two choices logRotate: reopen or rename, but both the case you need to run below mention code to rotate the log.

db.adminCommand( { logRotate : 1 } )

Either you need to execute this code manually or you need to write a corn schedule job to do this periodically. Now I am showing you how do you automate mongodb log file rotation in your linux VM without writing any shell script and corn job scheduler.

MongoDB Automation Logrotate

For this log rotation automation, I used logrotate mechanism which are available in most of the linux distribution.

Mongdb configuration

In mongodb configuration file ( mongod.conf or mongos.conf ) at the systemLog section I provided below configuration. My log file path is /var/mongodb/log/mongod.log . After below changes, do not forget to restart the mongod or mongos process once again.

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

Now create this file below, here mongodb is linux user name.

sudo nano /etc/logrotate.d/mongodb

In this file make this changes

/var/mongodb/log/mongod.log
{
   rotate 10
   daily
   dateext
   dateformat %Y-%m-%d-%s
   dateyesterday
   size 10000M
   missingok
   create 600 mongodb mongodb
   delaycompress
   compress
   sharedscripts
   postrotate
     /bin/kill -SIGUSR1 $(cat /var/run/mongodb.pid)
   endscript
}

pid file path for MongoDB

You will find this file to your data directory, in my case /data/db

/data/db/mongod.lock

Adding a simple file link will do the trick for me.

ln -s /data/db/mongod.lock /var/run/mongodb.pid

Now, this is linked to $(cat /var/run/mongodb.pid) of the logrotate setup file /etc/logrotate.d/mongodb which you are currently editing.

Explain /etc/ logrotate.d/mongodb Parameter

Now test the logfile rotation, does it work properly or not?

 logrotate --force /etc/logrotate.d/mongodb

It should be look like this

-rw------- 1 mongodb mongodb 5.5M Sep 13 11:57 mongod.log
-rw------- 1 mongodb mongodb 1.9K Sep 13 12:19 mongod.log2020-09-11-1599913164.gz
-rw------- 1 mongodb mongodb 1.4K Sep 13 12:19 mongod.log2020-09-12-1599913195

Troubleshooting

You need to check with below command should rotate the log file.

sudo logrotate --force /etc/logrotate.d/mongodb

You can also troubleshoot by making debug flag on, and try to fix error for the logrotation by this command

sudo logrotate -d /etc/logrotate.d/mongodb

You can also face something like every thing you done it correctly and when you make the -f or –force command it will work, but it will not work at regular interval. Then you have just last resort measure to make this fired by cron job scheduler.

crontab -e // Open linux cron file
59 23 * * * sudo logrotate --force /etc/logrotate.d/mongodb //add this line if you need to rotate the log daily basis.
or
0 */1 * * * sudo logrotate --force /etc/logrotate.d/mongodb  // add this line if you want to rotate the log in hourly basis.

For cron scheduler timing you can check this site.