{"id":1849,"date":"2010-11-16T20:42:26","date_gmt":"2010-11-16T19:42:26","guid":{"rendered":"http:\/\/www.devco.net\/?p=1849"},"modified":"2010-11-16T20:42:26","modified_gmt":"2010-11-16T19:42:26","slug":"mcollective_as_a_ha_service_locator","status":"publish","type":"post","link":"https:\/\/www.devco.net\/archives\/2010\/11\/16\/mcollective_as_a_ha_service_locator.php","title":{"rendered":"MCollective as a HA service locator"},"content":{"rendered":"

I am working toward releasing The Marionette Collective 1.0.0 and finishing off a last few features. I’ll maintain 1.0.0 as a long term supported stable version while 1.1.x will be where new development will happen.<\/p>\n

One of the last features that will go into 1.0.0 is the ability to do a discovery but then only target a subset of hosts.<\/p>\n

I have a Nagios Notification system called Angelia<\/a> and I have three instances of this deployed on my network. Any machine that needs to send a message can do this via the angelianotify<\/em> agent. I need the Angelia service to be highly available so that even if I do maintenance on one instance the others should transparently keep sending my alerts.<\/p>\n

The problem is that till now I had to filter based on enough state to uniquely identify a single instance of Angelia else I will receive multiple alerts, this new feature solves this problem.<\/p>\n

<\/p>\n

\r\n$ mc-rpc -1 angelianotify sendmsg msg=\"hello world\" recipient=\"clickatell:\/\/0044xxx\"\r\n<\/pre>\n
<\/code><\/p>\n
With the new -1<\/em> flag a discovery will be done, it will find 3 instances and by default it will pick the the node that was quickest to respond.  This is a poor mans nearest<\/em> detection.  You can also configure it to send the request to a random node in the results.<\/p>\n
The -1<\/em> is shorthand for another option, the full option is –limit-nodes 1<\/em> so you can specify any arbitrary number of nodes but you can also specify something like –limit-nodes 10%<\/em> to only hit a subset of your machines.<\/p>\n
The percentage targeting is useful for only initiating deploys against a subset of your nodes while your monitoring system detects errors before you do your full deploy to all your servers.<\/p>\n
This was a simple thing to implement but I think it’s a pretty big deal – it helps us step further away from DNS as an addressing system and rather use your metadata.<\/p>\n
It also means if you’re exposing services over SimpleRPC you can now easily create a very reliable network of these services using the communication layer provided by the middleware.  You can create a fully meshed network of ActiveMQ servers that can route around network outages, around maintenance windows and other outages without costly load balancers or without issues such as relying on locally redundant hosted instances of these services.<\/p>\n
With my Angelia example above – should my monitoring server in the US want to send an alert while I am doing maintenance on the nearest Angelia instance it will simply use the next nearest one, probably the one in the UK.  Effectively and cheaply realizing my need for a HA system over some arbitrarily simple bit of software like Angelia that doesn’t need to concern itself with being HA aware.<\/p>\n","protected":false},"excerpt":{"rendered":"
I am working toward releasing The Marionette Collective 1.0.0 and finishing off a last few features. I’ll maintain 1.0.0 as a long term supported stable version while 1.1.x will be where new development will happen. One of the last features that will go into 1.0.0 is the ability to do a discovery but then only […]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_et_pb_use_builder":"","_et_pb_old_content":"","footnotes":""},"categories":[1],"tags":[121,78,13],"_links":{"self":[{"href":"https:\/\/www.devco.net\/wp-json\/wp\/v2\/posts\/1849"}],"collection":[{"href":"https:\/\/www.devco.net\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.devco.net\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.devco.net\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.devco.net\/wp-json\/wp\/v2\/comments?post=1849"}],"version-history":[{"count":3,"href":"https:\/\/www.devco.net\/wp-json\/wp\/v2\/posts\/1849\/revisions"}],"predecessor-version":[{"id":1852,"href":"https:\/\/www.devco.net\/wp-json\/wp\/v2\/posts\/1849\/revisions\/1852"}],"wp:attachment":[{"href":"https:\/\/www.devco.net\/wp-json\/wp\/v2\/media?parent=1849"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.devco.net\/wp-json\/wp\/v2\/categories?post=1849"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.devco.net\/wp-json\/wp\/v2\/tags?post=1849"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}