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Re: gear creation on nodes



Other replies have talked about current developments in Origin. If you're looking at production usage, you will probably be considering OpenShift Enterprise, which for stability will generally be a little behind. The features in discussion here won't be in OSE until version 1.2 at least.

The existing OSE gear placement algorithm is described here:
https://access.redhat.com/knowledge/docs/en-US/OpenShift_Enterprise/1.0/html-single/Administration_Guide/index.html#sect-OpenShift_Enterprise-Administration_Guide-Managing_Districts-Gear_Placement_Algorithm
Krishna's pointer to the actual algorithm is good, but go back a few months if you want to see how it shipped in OSE.

Note that there are options for enabling/disabling districts in /etc/openshift/plugins.d/openshift-origin-msg-broker-mcollective.conf as well as enabling/disabling non-district nodes when districts are enabled. The defaults should usually be reasonable.

As far as node host discovery - until Dan's change is complete, a node host is made discoverable by subscribing itself via mcollective. Gear placement requests are broadcast with a filter for node hosts to self-select according to their facts. With districts in play, one of the filters/facts is district. Other filters are for active_capacity and gear profile. So although with districts we have a registry of known nodes, that's not directly used yet. What really allows a node host to accept gears is its subscription to the broadcasts and the matching of its facts to the request filters.

----- Original Message -----
From: "meghdoot bhattacharya" <meghdoot_b yahoo com>
To: dev lists openshift redhat com
Sent: Monday, January 28, 2013 7:40:33 PM
Subject: gear creation on nodes




Hi, 
Given a set of nodes, when new gears are about to be created, what is the algorithm used to select the node? 


If brand new nodes/VM's are added later, how do those new nodes get discovered and made available to haproxy for future gear creation on those nodes? Does the mcollective in broker periodically send messages to discover new nodes or figure out if nodes are gone? 


Thx. 
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