monitoring mongodb and mysql replications using nagios I have set replication for mongoDB and mySQL.

Now I have to manage them using nagios. I have to write some php-script that will read server status. 

I am good with nagios setup. 

Now I want to know if there is some plugin that may ease my work, otherwise how exactly do I get the server status from nagios.

One solution I thought is to read the log file of nagios and look for pattern to know the server status, is it feasible?
For MongoDB, this would be a good place to start:

https://github.com/mzupan/nagios-plugin-mongodb

It's python rather than PHP, but it's basically what you are looking for to get the data into Nagios.  Then for what to monitor and alert on, I've previously written up a quick summary of this plugin previously on the mongodb-user group:

https://groups.google.com/forum/#!topic/mongodb-user/bix36VvywXE/discussion