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Hi Folks,

Dina Belova has recently landed some infra patches[1,2] to create
an experimental mongodb-based Tempest job. This effectively just
overrides the ceilometer storage backend config so that mongodb
is used instead of sql-alchemy. The new job has been running
happily for a few days so I'd like now to consider the path
forwards with this.

One of our Juno goals under the TC gap analysis was to more fully
gate against mongodb, given that this is the storage backend
recommended/supported by many distros. The sql-alchemy backend,
on the other hand, is more suited for proofs of concept or small
deployments. However up to now we've been hampered from reflecting
that reality in the gate, due to the gate being stuck on Precise
for a long time, as befits LTS, and the version of mongodb needed
by ceilometer (i.e. 2.4) effectively unavailable on that Ubuntu
release (in fact it was limited to 2.0.4).

So the orientation towards gating on sql-alchemy was mostly
driven by legacy issues in the gate's usage of Precise, as
opposed to this being considered the most logical basket in
which to put all our testing eggs.

However, we're now finally in the brave new world of Trusty :)
So I would like to make the long-delayed change over soon.

This would involve transposing the roles of sql-alchemy and
mongodb in the gate - the mongodb variant becomes the "blessed"
job run by default, whereas the sql-alchemy based job to
relegated to the second tier.

So my questions are:

 (a) would the QA side of the house be agreeable to this switch?

and:

 (b) how long would the mongodb job need to be stable in this
     experimental mode before we pull the trigger on swicthing?

If the answer to (a) is yes, we can get infra patches proposed
early next week to make the swap.

Cheers,
Eoghan

[1] https://review.openstack.org/#/q/project:openstack-infra/config+branch:master+topic:ceilometer-mongodb-job,n,z
[2] https://review.openstack.org/#/q/project:openstack-infra/devstack-gate+branch:master+topic:ceilometer-backend,n,z