On Wed, Sep 19, 2018 at 10:23 AM Cody <codeology.lab@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@redhat.com | redhat.com/openstack
dsneddon:irc | @dxs:twitter