Log Rotation to NFS Mount with Logrotate.d

Logrotate.d is one of the most flexible log rotation programs for linux servers. I recently was required to rotate a lot of large files daily from the server to a central NFS Mount and wanted to share just how easy this is to accomplish.

As background, this app is a Node.js application that uses Bunyon for a logging output plugin. Luckily, it accepts a USR2 signal to tell it "hey, I just rotated your log file, make a new one and keep on truckin'". See, the first issue is that moving a file that a process is writing to, simply renames where the inode is pointing, so your process will continue writing to the new filename as if nothing happened. Telling it to make a new file is key to rotation.

The following code block is the entirety of my logrotate.d script. Placed in the /etc/logrotate.d/ folder, it will be read in and processed every night. I've used the date command to create sub dirs per month to keep things organized in the long term, and the hostname to put them each in their own directories per hostname.

/var/log/myApp/*log {
    daily
    dateext
    rotate 7
    missingok
    compress
    sharedscripts
    postrotate
        [ ! -f /var/run/myApp.pid ] || kill -USR2 `cat /var/run/myApp.pid`
    endscript
    lastaction
 mkdir -p /logsMount/myApp/`hostname`/`date +%Y\/%m`/
 mv /var/log/myApp/*gz /logsMount/myApp/`hostname`/`date +%Y\/%m`/ 
    endscript
}

As this reads, top down: For all files ending in "log" in the /var/log/myApp directory, on a daily basis, throw a date extension on them (-20150102 for instance. Not putting 'dateext' will cause it to simply number them .1, .2, etc.), keep the last 7 days (useful if the nfs mount goes down). If the files are missing don't throw an error. Compress the files (with gzip by default). As your Post Rotate command, send a signal to the process ID noted in the /var/run/myApp.pid file to tell that process to regenerate it's logs. Then, when that's done, make sure there's a directory on the target nfs mount and move all .gz files to it.

It's important to note that the 'postrotate' commans occur AFTER file rotation, but PRIOR to compression. the 'lastaction' section occurs as the last thing it does in this script, i.e. after all other things are done including compression.

This will move things like: /var/log/myApp/myLogFile.log -> /logsMount/myApp/myHost/2015/01/myLogFile.log-20150102.gz

Hope this helps someone out!