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HA with 2 controller nodes (deployed by Fuel7)?

asked 2015-11-12 18:51:38 -0500

redondo-mk gravatar image

Hi!

Although high-availability configuration with 2 nodes should not be recommended for production I would like to know if anybody is using it. My current idea is to implement it in the private data center which is critical for development team but is not critical for true high available service. I would like to have 2 controllers because this servers are relatively old and I would like to have one available if the other one dies.

Is it just MySQL that is using Galera which requires 3 nodes the issue here? I wonder whether it would be a good option to make deployment with Fuel and then replace Galera with DRBD?

If anybody is using HA deployed with Fuel7 on 2 controllers, please share any experiences or information or if anybody knows what exact issues can I expect and where I can find more information to overcome those issues, let me know.

Thanks!

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answered 2015-11-16 08:11:59 -0500

capsali gravatar image

You can not have HA with 2 nodes. You will achieve falt-tolerance with this setup. But if one node goes down you will have locked services especially with galera cluster, that locks db when there is only one mysql node available to not allow corruption to occur. Other services will also lock untill the node is back online (rabbitmq, memcache etc., openstack services aswell).

But it will preserve the last state of services untill the second controller comes back online!

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So, having 2 controllers (VLAN provider net) and 1 controller dies and needs to be replaced, VMs will be available but to unlock the active controller I will have to do some serious work or can I just remove failed node from Fuel env and Fuel will reconfigure active controller to play as a single?

redondo-mk gravatar imageredondo-mk ( 2015-11-16 14:33:57 -0500 )edit

Well i never used fuel but i am almost certain that fuel will not reconfigure the enveironment to run on one controller on the fly. In a 2 controller fault-tolarance setup, if one goes down, your instances will keep running but i cannot say the same for FIP's. It really depends if fuel HA deploys

capsali gravatar imagecapsali ( 2015-11-17 03:35:41 -0500 )edit

l3_ha agents. If this is the case than you will have external connectivity aswell assuming both external network on the controllers are on the same switch. You will than need to add the second controller back online. The most important is galera cluster which unlocks when the second master is online

capsali gravatar imagecapsali ( 2015-11-17 03:38:45 -0500 )edit

If i remember correctly last time i checked fuel it wouldn't let you configure HA openstack with just 2 controller nodes!

capsali gravatar imagecapsali ( 2015-11-17 03:39:24 -0500 )edit

"Use at least three controller nodes for high-availability. For all deployments, the total number of the controller nodes must be odd." Deployment in my case with 2 nodes fails with error as seen in https://bugs.launchpad.net/fuel/+bug/1494764 (bug). I have all the answers I believe. Thanks Capsai!

redondo-mk gravatar imageredondo-mk ( 2015-11-18 12:41:17 -0500 )edit

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Asked: 2015-11-12 18:51:38 -0500

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Last updated: Nov 16 '15