[Openstack-operators] memcached redundancy

Joe Topjian joe at topjian.net
Thu Aug 14 16:09:59 UTC 2014


I have an OpenStack cloud with two HA cloud controllers. Each controller
runs the standard controller components: glance, keystone, nova minus
compute and network, cinder, horizon, mysql, rabbitmq, and memcached.

Everything except memcached is accessed through haproxy and everything is
working great (well, rabbit can be finicky ... I might post about that if
it continues).

The problem I currently have is how to effectively work with memcached in
this environment. Since all components are load balanced, they need access
to the same memcached servers. That's solved by the ability to specify
multiple memcached servers in the various openstack config files.

But if I take a server down for maintenance, I notice a 2-3 second delay in
all requests. I've confirmed it's memcached by editing the list of
memcached servers in the config files and the delay goes away.

I'm wondering how people deploy memcached in environments like this? Are
you using some type of memcached replication between servers? Or if a
memcached server goes offline are you reconfiguring OpenStack to remove the
offline memcached server?

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