[rdo-users] [TripleO] Scaling custom roles with Pacemaker managed services

[Dan Sneddon]

On Wed, Sep 19, 2018 at 10:23 AM Cody <codeology.lab at gmail.com> wrote:

> Hello there,
>
> I have another question about scaling TripleO.
>
> According to the TripleO documentation for RHOPS 13/Queens [1], "you
> cannot scale up or scale down a custom role that contains
> OS::TripleO::Services::Pacemaker or
> OS::TripleO::Services::PacemakerRemote services."
>
> Does that only apply to the role itself or the pcmk-managed services
> within the role? For instance, if I already have 3 nodes running DB
> and messaging services with a composable HA role, can I later create
> another custom role just to scale up the messaging service again?
>
> Thank you very much!
>
> [1]
> https://access.redhat.com/documentation/en-us/red_hat_openstack_platform/13/html/advanced_overcloud_customization/roles#sect-Composable_Services-Guidelines
>
> Regards,
> Cody
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It applies to all services which are managed by Pacemaker, including the
associated virtual IPs. The same services that can be separated from the
Pacemaker services are the ones that can be moved to other roles and don't
have the same scaling constraints. For instance, you could probably add X
additional API worker nodes in a custom role, and they would be added as
back-ends behind HAProxy, but you couldn't add any HAProxy nodes, since
Pacemaker manages the virtual IPs that HAProxy binds to. Unfortunately,
Pacemaker manages Rabbit MQ, so you are stuck with 3 nodes.

-- 
Dan Sneddon         |  Senior Principal OpenStack Engineer
dsneddon at redhat.com |  redhat.com/openstack
dsneddon:irc        |  @dxs:twitter
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