[Openstack-operators] HA solutions for L3-Agent and metadata-agent ?

Jesse Pretorius jesse.pretorius at gmail.com
Fri Mar 7 09:07:31 UTC 2014

On 6 March 2014 14:54, Alvise Dorigo <alvise.dorigo at pd.infn.it> wrote:

> As stated in the mentioned thread there's no solution for making L3 agent
> HA with the active/active paradigm. But I have to use the active/active
> paradigm.

There is a blueprint for a fully active-active L3 Agent that's close to

> In the mentioned thread, Jay suggests to use a tool to replicate l3
> agent's status to the other node upon failure of the current node (I
> haven't used this tool yet).

We use this in production and it works well. Essentially it doesn't give
you true active-active high availability, but it does give you automated
redundancy and you are able to use multiple L3 Agents actively.
The path for packets will only every use one L3 Agent at a time, but if an
Agent goes down, the tool will migrate the L3 Agent servicing the virtual
routers to an alternative active agent. The tenant/project's L3 traffic
will be lost only for the duration of the down-time detection and move. If
the tool is run every minute in cron, the detection will happen within a
minute. It has a random wait period of less than a minute before starting a
move. The time it take for the move itself to complete depends on how many
virtual routers need to be moved.

> Reading the HA guide by Openstack (
> http://docs.openstack.org/high-availability-guide/content/_running_neutron_metadata_agent.html)
> there's not a solution active/active-based also for the metadata agent.

The metadata agent is stateless and can be implemented in an active-active
manner with load balancing using something like haproxy. We do this
successfully in production.
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