The document discusses monitoring tools Nagios and Sensu. It notes several limitations with Nagios, including a lack of active-active clustering and needing to restart after adding hosts. Sensu is presented as an alternative that supports active-active clustering, automatic host registration, distributing check execution across clients, and easier configuration using JSON files. The document provides an overview of Sensu's architecture, modes of operation, handlers, mutators, extensions, and some remaining limitations.

1. Monitoring with

2. First of all...

3. First of all...

4. Why we (me) don’t like Nagios?
• No active-active cluster

5. Why we (me) don’t like Nagios?
• No active-active cluster (nor easy active-passive one)

6. Why we (me) don’t like Nagios?
• No active-active cluster (nor easy active-passive one)

7. Why we (me) don’t like Nagios?
• No active-active cluster (nor easy active-passive one)
• Restart after adding a host (auto-scaling
anyone??)

8. Why we (me) don’t like Nagios?
• No active-active cluster (nor easy active-passive one)
• Restart after adding a host (auto-scaling
anyone??)
• (Really) difficult to hack on

9. Why we (me) don’t like Nagios?
• The master executes the checks (all of them!)

10. Why we (me) don’t like Nagios?
• The master executes the checks (all of them!)
• Painful config reloads if using slaves

11. Why we (me) don’t like Nagios?
• The master executes the checks (all of them!)
• Painful config reloads if using slaves
• (Quite) hard to configure

12. Why we (me) don’t like Nagios?
• First release: March 14, 1999

13. Why we (me) don’t like Nagios?
• First release: March 14, 1999

15. What’s Sensu?
• A monitoring framework
• They say “monitoring router”
• It takes results of checks and passes them to
handlers

16. Sensu facts
• Active-active cluster

17. Sensu facts
• Active-active cluster
• Hosts automagically registered when agent
starts

18. Sensu facts
• Active-active cluster
• Hosts automagically registered when agent
starts
• Written in Ruby

19. Sensu facts
• Clients execute all the checks (all of them!)

20. Sensu facts
• Clients execute all the checks (all of them!)
• No need to have slaves (but you can if you
want to)

21. Sensu facts
• Clients execute all the checks (all of them!)
• No need to have slaves (but you can if you
want to)
• Configured with small JSON files

22. Sensu facts
• Clients execute all the checks (all of them!)
• No need to have slaves (but you can if you
want to)
• Configured with small JSON files
• Compatible with Nagios plugins!

23. Sensu facts
• IT’S 2014

24. Sensu facts
• IT’S 2014

25. What does Sensu provide?
• Agent (client) to gather check results
• Server to take actions (or not) on these results
• REST API to query the state
• Optional dashboard to query the API

26. What does Sensu NOT provide?
• Storage for the results history
• Notifications
• Graphing

27. Architecture overview

28. Two modes of operation

29. Subscription
subscription messages

30. Subscription
check request

31. Subscription
check results

32. Standalone

33. Standalone
check results

34. • Modes can be mixed
• The client also listens for results in a socket
– Throw JSON to it from your application

36. Handlers
• Each check can have its own handler
• Sensu considers only results flagged as
“metrics” and not-ok’s

37. Handler types
• Pipe: the server executes a script and throws
the event as JSON to the standard input
• TPC and UDP: the server connects to a host
and port and delivers the event
• AMQP: the event can be reinjected in the
broker for further routing

39. Handling events selectively
• What if you don’t want to handle some
events?
• REST API to the rescue

40. Stashes
• A stash is associated with an ID (a “path”)
• You can store here as much shit as you want
• Put a “silence” in the stash, and make your
handlers check for it.

41. Mutators
• A filter to modify event data before passing it
to a handler.
• Example: manipulate events to make them
suitable for graphite before passing them to a
TCP handler

42. Extensions
• Mutators and Handlers running in the same
process than Sensu
• They must be written also in Ruby
• Run in the same event loop

44. Things missing / rant
• You can’t monitor something if you can’t
install an agent on it.
– There’s a ticket open since more than one year
ago...
– Some patches, but still not a solution
• As with nagios, the state is decided by the
plugins.

45. Further research
• http://sensuapp.org/docs/0.12
• https://github.com/sensu
• http://sensuapp.org/support/
• https://metacpan.org/pod/Sensu::API::Client