Open Stack

+1 for using k8s to do work where possible.

-1 for trying to shoehorn a feature in so that k8s can deal with stuff its not ready to handle. We need to ensure Operators have everything they need in order to successfully operate their cloud.

The current upgrade stuff in k8s is focused around replacing one, usually stateless, thing for another. It never had Database Schema upgrades in mind.  It is great to use for minor version bumps. It is insufficient for major OpenStack upgrades. If you follow the OpenStack release notes, they tend to be quite linear, in a workflow. K8s isn't designed for that. Hence the need for a tool outside of k8s to drive the creation/upgrading of Deployments and Jobs in the proper order.

Init containers also do not look like a good fit. As far as I can gather from the spec, they are intended to init something on a node when a pod is spawned. This is a very different thing from upgrading a shared database's schema. I don't believe they should be used for that.

I've upgraded many OpenStack clouds over the years. One of the things that has bit me from time to time is a failed schema update and having to tweak code and then rerun schema upgrades. This will continue to happen and needs to be covered. The Job's workflow as discussed in the spec allows an operator to do just that. Hiding it in an init container makes that much harder for Operators.

As an Op, we need the ability to tweak the workflow as needed and run/rerun only the pieces that we need.

Thanks,
Kevin
________________________________________
From: Ryan Hallisey [rhallise at redhat.com]
Sent: Sunday, May 22, 2016 12:50 PM
To: OpenStack Development Mailing List (not for usage questions)
Subject: [openstack-dev]  [kolla][kolla-kubernetes][kubernetes]

Hi all,

At the Kolla meeting last week, I brought up some of the challenges around the bootstrapping
process in Kubernetes.  The main highlight revolved around how the bootstrapping process will
work.

Currently, in the kolla-kubernetes spec [1], the process for bootstrapping involves
outside orchestration running Kubernetes 'Jobs' that will handle the database initialization,
creating users, etc...  One of the flaws in this approach, is that kolla-kubernetes can't use
native Kubernetes upgrade tooling. Kubernetes does upgrades as a single action that scales
down running containers and replaces them with the upgraded containers. So instead of having
Kubernetes manage the upgrade, it would be guided by an external engine.  Not saying this is
a bad thing, but it does loosen the control Kubernetes would have over stack management.

Kubernetes does have some incoming new features that are a step in the right direction to
allow for kolla-kubernetes to make complete use of Kubernetes tooling like init containers [2].
There is also the introduction to wait.for conditions in the kubectl [3].

       kubectl get pod my-pod --wait --wait-for="pod-running"

Upgrades will be in the distant future for kolla-kubernetes, but I want to make sure the
community maintains an open mind about bootstrap/upgrades since there are potentially many
options that could come down the road.

I encourage everyone to add your input to the spec!

Thanks,
Ryan

[1] SPEC - https://review.openstack.org/#/c/304182/
[2] Init containers - https://github.com/kubernetes/kubernetes/pull/23567
[3] wait.for kubectl - https://github.com/kubernetes/kubernetes/issues/1899

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