Hi Sergey! Comments inline.
On 11/20/2014 05:25 AM, Sergey Vasilenko wrote:
Nor should it, IMO. Other than the Neutron dhcp-agent, all OpenStack
services that run on a "controller node" are completely stateless.
Therefore, I don't see any reason to use corosync/pacemaker for
management of these resources.
I see following reasons for managing neutron agents by Pacemaker:
Completely agree with you here for the Neutron agents, since they are
not the same as the other OpenStack controller services. The Neutron
agents keep state, and therefore are appropriate for management by
Pacemaker, IMO.
* *co-location* between resources. For example, L3 and DHCP agents
should be run only on nodes, that has properly work openvswitch (or
another L2) agent. Then L2-agent works wrong -- L3 and DHCP agents
should be stopped immediately. Because Neutron don't control this
situation and can allocate some resources (router or subnet) to an
agent.
* extended *monitoring*. Traditional OS init/upstart subsystem allow
only simple status checking (may be exclude systemd). Now we have
situation, for example with neutron agents, then some of
agent pretends to well-working. But in really, do nothing.
(unfortunately, openstack developed as is) Such agent should be
immediately restarted. Our Neutron team now works on internal
health-checking feature for agents, and I hope, that this will
implemented in 6.1. For example we can make simple checking (pid
found, process started) every 10sec, and more deep (RMQ connection,
internal health-checking) -- mo rare.
* No different business-logic for different OS. We can use one OCF
script for Ubuntu, Centos, debian, etc...
* handle cluster partitioning situation.
haproxy should just spread the HTTP request load evenly across all
API services and things should be fine, allowing haproxy's http
healthcheck monitoring to handle the simple service status checks.
Just HTTP checking not enough. In the future will be better make more
deep checking personal for each openstack service.
For endpoints that need more than an HTTP check, absolutely, you are
correct. But, in real life, I haven't really seen much need for more
than an HTTP check for the controller services *except for the Neutron
agents*.
All the best,
-jay
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