Open Stack

On 02/13/2018 05:08 PM, Armando M. wrote:
> 
> 
> On 13 February 2018 at 14:02, Brent Eagles <beagles at redhat.com 
> <mailto:beagles at redhat.com>> wrote:
> 
>     Hi,
> 
>     The neutron agents are implemented in such a way that key
>     functionality is implemented in terms of haproxy, dnsmasq,
>     keepalived and radvd configuration. The agents manage instances of
>     these services but, by design, the parent is the top-most (pid 1).
> 
>     On baremetal this has the advantage that, while control plane
>     changes cannot be made while the agents are not available, the
>     configuration at the time the agents were stopped will work (for
>     example, VMs that are restarted can request their IPs, etc). In
>     short, the dataplane is not affected by shutting down the agents.
> 
>     In the TripleO containerized version of these agents, the supporting
>     processes (haproxy, dnsmasq, etc.) are run within the agent's
>     container so when the container is stopped, the supporting processes
>     are also stopped. That is, the behavior with the current containers
>     is significantly different than on baremetal and stopping/restarting
>     containers effectively breaks the dataplane. At the moment this is
>     being considered a blocker and unless we can find a resolution, we
>     may need to recommend running the L3, DHCP and metadata agents on
>     baremetal.

I didn't think the neutron metadata agent was affected but just the 
ovn-metadata agent?  Or is there a problem with the UNIX domain sockets 
the haproxy instances use to connect to it when the container is restarted?

> There's quite a bit to unpack here: are you suggesting that running 
> these services in HA configuration doesn't help either with the data 
> plane being gone after a stop/restart? Ultimately this boils down to 
> where the state is persisted, and while certain agents rely on 
> namespaces and processes whose ephemeral nature is hard to persist, 
> enough could be done to allow for a non-disruptive bumping of the afore 
> mentioned services.

Armando - https://review.openstack.org/#/c/542858/ (if accepted) should 
help with dataplane downtime, as sharing the namespaces lets them 
persist, which eases what the agent has to configure on the restart of a 
container (think of what the l3-agent needs to create for 1000 routers).

But it doesn't address dnsmasq being unavailable when the dhcp-agent 
container is restarted like it is today.  Maybe one way around that is 
to run 2+ agents per network, but that still leaves a regression from 
how it works today.  Even with l3-ha I'm not sure things are perfect, 
might wind-up with two masters sometimes.

I've seen one suggestion of putting all these processes in their own 
container instead of the agent container so they continue to run, it 
just might be invasive to the neutron code.  Maybe there is another option?

-Brian