On 24/08/15 15:12, Emilien Macchi wrote:
Hi,

So I've been working on OpenStack deployments for 4 years now and so far
RDO Manager is the second installer -after SpinalStack [1]- I'm working on.

SpinalStack already had interested features [2] that allowed us to
upgrade our customer platforms almost every months, with full testing
and automation.

Now, we have RDO Manager, I would be happy to share my little experience
on the topic and help to make it possible in the next cycle.

For that, I created an etherpad [3], which is not too long and focused
on basic topics for now. This is technical and focused on Infrastructure
upgrade automation.

Feel free to continue discussion on this thread or directly in the etherpad.

[1] http://spinalstack.enovance.com
[2] http://spinalstack.enovance.com/en/latest/dev/upgrade.html
[3] https://etherpad.openstack.org/p/rdo-manager-upgrades

I added some notes on the etherpad, but I think this discussion poses a larger question: what is TripleO? Why are we using Heat? Because to me the major benefit of Heat is that it maintains a record of the current state of the system that can be used to manage upgrades. And if we're not going to make use of that - if we're going to determine the state of the system by introspecting nodes and update it by using Ansible scripts without Heat's knowledge, then we probably shouldn't be using Heat at all.

I'm not saying that to close off the option - I think if Heat is not the best tool for the job then we should definitely consider other options. And right now it really is not the best tool for the job. Adopting Puppet (which was a necessary choice IMO) has meant that the responsibility for what I call "software orchestration"[1] is split awkwardly between Puppet and Heat. For example, the Puppet manifests are baked in to images on the servers, so Heat doesn't know when they've changed and can't retrigger Puppet to update the configuration when they do. We're left trying to reverse-engineer what is supposed to be a declarative model from the workflow that we want for things like updates/upgrades.

That said, I think there's still some cause for optimism: in a world where every service is deployed in a container and every container has its own Heat SoftwareDeployment, the boundary between Heat's responsibilities and Puppet's would be much clearer. The deployment could conceivably fit a declarative model much better, and even offer a lot of flexibility in which services run on which nodes. We won't really know until we try, but it seems distinctly possible to aspire toward Heat actually making things easier rather than just not making them too much harder. And there is stuff on the long-term roadmap that could be really great if only we had time to devote to it - for example, as I mentioned in the etherpad, I'd love to get Heat's user hooks integrated with Mistral so that we could have fully-automated, highly-available (in a hypothetical future HA undercloud) live migration of workloads off compute nodes during updates.

In the meantime, however, I do think that we have all the tools in Heat that we need to cobble together what we need to do. In Liberty, Heat supports batched rolling updates of ResourceGroups, so we won't need to use user hooks to cobble together poor-man's batched update support any more. We can use the user hooks for their intended purpose of notifying the client when to live-migrate compute workloads off a server that is about to upgraded. The Heat templates should already tell us exactly which services are running on which nodes. We can trigger particular software deployments on a stack update with a parameter value change (as we already do with the yum update deployment). For operations that happen in isolation on a single server, we can model them as SoftwareDeployment resources within the individual server templates. For operations that are synchronised across a group of servers (e.g. disabling services on the controller nodes in preparation for a DB migration) we can model them as a SoftwareDeploymentGroup resource in the parent template. And for chaining multiple sequential operations (e.g. disable services, migrate database, enable services), we can chain outputs to inputs to handle both ordering and triggering. I'm sure there will be many subtleties, but I don't think we *need* Ansible in the mix.

So it's really up to the wider TripleO project team to decide which path to go down. I am genuinely not bothered whether we choose Heat or Ansible. There may even be ways they can work together without compromising either model. But I would be pretty uncomfortable with a mix where we use Heat for deployment and Ansible for doing upgrades behind Heat's back.

cheers,
Zane.


[1] http://www.zerobanana.com/archive/2014/05/08#heat-configuration-management

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