Monitoring Rails Apps: Pulse + More 1

Posted by aaron
on Friday, October 26
Paul Gross from Thoughtworks recently created a pulse gem. The gem adds a simple action to your rails app, "/pulse", which acts as a heartbeat.

The pulse gem currently defines the method as: 
def pulse
   render :text => "OK"
end
Then you can configure haproxy to monitor your application by hitting http://server/pulse and verifying the response is "OK".

We've had a similar action in our applications for quite some time, although I really like the idea of externalizing it to a gem. Our implementation is slightly different though. Since so many rails applications depend on a database, I instead added: 
def pulse
    rows = ActiveRecord::Base.connection.execute("select 1 from dual").num_rows rescue 0
    render :text => rows == 1 ? "OK" : "Error!"
end
IIRC, "select 1 from dual" is the fastest query you can run against a database, in MySQL, Oracle, and Postgres. And if you have mutliple databases, you can add union in the one pulse request, or have multiple actions.

Now you are not only testing your application is live, but that it can connect to the database.
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  1. Will Green – October 28, 2007 @ 11:15 AM
    So, what does haproxy do if gets back an error? Does it restart your db, or email you?
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