Open Stack

On Tue, Aug 13, 2019 at 11:44:36AM +0200, Shadi Akiki wrote:
> 2- how the allocated resource can be downsized (which I was hoping to find
> in the opendev/system-config <https://opendev.org/opendev/system-config>
>  repo)

You are correct that the sizing details for control plane servers are
not really listed anywhere.

This is really an artifact of us manually creating control-plane
servers.  When we create a new control-plane server, we use the launch
tooling in [1] where you will see we manually select a flavor size.
This is dependent on the cloud we launch the server in and the flavors
they provide us.

There isn't really a strict rule on what flavor is chosen; it's more
art than science :) Basically the smallest for what seems appropriate
for what the server is doing.

After the server is created the exact flavor used is not recorded
separately (i.e. other than querying nova directly).  So there is no
central YAML file or anything with the server and the flavor it was
created with.  Sometimes the cloud provider will provide us with
custom flavors, or ask us to use a particular variant.

So in terms of resizing the servers, we are limited to the flavors
provided to us by the providers, which varies.  In terms of the
practicality of resizing, as I'm sure you know this can be harder or
easier depending on a big variety of things from the provider.  We
have resized servers before when it becomes clear they're not
performing (recently adding swap to the gitea servers comes to mind).
Depending on the type of service it varies; for something not
load-balanced that requires production downtime, it's a very manual
process.

Nobody is opposed to making any of this more programatic, I'm sure.
It's just a trade-off between development time to create and maintain
that, and how often we actually start control-plane servers.

In terms of ask.o.o, that is a "8 GB Performance" flavor, as defined
by RAX's flavors.  This was rebuilt when we upgraded it to Xenial as
an 8GB node (from 4GB) as investigation at the time showed 4GB was a
bit tight [2].  8GB is the next quanta up of flavor provided by RAX
over 4GB.

I hope this helps!

-i

[1] https://opendev.org/opendev/system-config/src/branch/master/launch
[2] http://lists.openstack.org/pipermail/openstack-dev/2018-April/129078.html