[marathon] service checks and improvements

[gphat]

What's This Do?

After working on the just-merged etcd plugin for #1235 I wanted to take a look at the Marathon plugin. Looks like the key problem I saw was already fixed in #1240. While I was here I:

• Refactored some of the magic numbers and arrays up into class variables
• Removed unnecessary includes
• Switched to the service check API
• Added the "disk" attribute from the metrics

Thanks!

I appreciate you taking the time to look at this. If I can do anything to help a merge, let me know!

[LeoCavaille]

This compat can be dropped, also as get_v2_apps and get_v2_app_versions could be refactored in one single function with the endpoint as argument because they are the same.

Also that would be the occasion to drop timeout_event and status_code_event and inline the service checks directly in the function above. Wdyt?

[LeoCavaille]

Hi @gphat , me again 😉
Thanks for the improvements, could you look at the few comments I made?

[gphat]

All great feedback as usual @LeoCavaille. Thanks for the suggestions. Pretty soon you'll have to give fewer of them.

[gphat]

This looks good locally

   marathon
    --------
      - instance #0 [OK]
      - Collected 137 metrics, 0 events & 1 service check

[LeoCavaille]

Hey @gphat, looking again at your PR, there are just a few things missing:

• you report a service check only for critical state but never an OK state
• the service check is tagged by url in the get_json functino which means that we will report different service checks for the different urls, do we want that? Maybe we could just tag by the url base and not the full URL ?
• to be more readable APP_METRICS could be wrapped and sorted like

APP_METRICS = [
    'a',
    'b',
]

• also can you rebase and squash your commits against the current master, it looks like you have a merge conflict of some sort

Thanks

[gphat]

Somehow I've botched my merge and screwed things up. Lemme resend this. :)

[gphat]

Sorry for moving this, I suck. This is replaced by #1296.