Monitor mongo w/monit

mongo_replSetGetStatus.rb

#!/usr/bin/env ruby
## used by monit to check for unhealthy cluster state 

require 'rubygems'
require 'mongo'

begin
  db = Mongo::Connection.new("localhost", 27017, :op_timeout => 3).db("admin")
rescue
  abort("MongoDB Connection Error: #{$!}")
else
  health = db.command('serverStatus' => 1)
  state = db.command('replSetGetStatus' => 1)

  # comb the entire output for any bad error messages && make sure we got a response
  if (health.to_s =~ /not reachable\/unhealthy/ or health.nil?)
  then
    abort("Found 'not reachable/unhealthy' node, or health.nil? => true")
  # check my state, >2 is generally not good, && make sure we got a response
  elsif (state['myState'].to_i > 2 or state['myState'].nil?)
  then
    abort("Found 'myState > 2', or state['myState'].nil? => true")
  # everything looks jolly, exit cleanly
  else
    exit 0
  end

end

monit.conf

## Mongo cluster state
check program prod_mongodb_cluster_health with path "/some/path/to/bin/monit/mongo_replSetGetStatus.rb"
  if status != 0 timeout 3 seconds for 2 cycles then alert