add per-client subscriptions

[cwjohnston]

This change set implements the per-client subscription feature as described in
sensu/sensu#1327:

The Sensu client should automatically create a subscription called
clint:client-name (e.g. client:i-424242) for every client. This will allow
for other features in Sensu to target specific clients or groups of clients
using subscriptions.

This feature is intended to support per-client silencing via the new silence API
described in sensu/sensu#1328

[portertech]

I am not a fan of tacking this onto load_client_env(), perhaps it should live in a method like load_client_overrides() etc?

[cwjohnston]

@portertech I've moved the implementation into its own method. Are tests 👌 as-is?

[runningman84]

Please make the optional or add some kind of standalone mode as I my pull request does. Otherwise this feature will break snssqs transport.

[portertech]

@runningman84 a Sensu Transport that does not support Sensu's model must be able to handle such actions with an appropriate no-op.

[runningman84]

@portertech I have already done some modifications in order to handle this. But I need to know if the process is running in a client or server in order to handle things differently. Can you pass the type to the transport or is there a method to find this out?

[portertech]

@cwjohnston 👍

[portertech]

@cwjohnston the new method is still being called from within load_env(), which is no good, as configuration will still override the subscriptions. Check out the application order:

sensu-settings/lib/sensu/settings.rb

Line 15 in cd7525c

@loader.load_env

[runningman84]

@portertech this are my modifications:
runningman84/sensu-transport-snssqs@56c4518
General speaking it seems to work but the sensu client has 100% CPU load. Maybe I messed up some EM stuff. Do you see any problem in my code? As you can see I need to know if it is running as a client or server.

[troyready]

@runningman84 see Sean's suggestion at sensu/sensu#1327 (comment)

I could try to whip up a sensu-transport-snssqs PR for it unless you'd like to?

[runningman84]

@troyready a PR would be really great. My ruby EM knowhow is quite limited.

[cwjohnston]

The sensu-transport-snssqs issues are presumed to be resolved with v2.0.4 earlier today. @portertech is this ready to go?

[portertech]

@cwjohnston this looks good.