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[TripleO] Scaling node counts with only Ansible (N=1)


On Sat, 2019-07-13 at 16:19 -0400, James Slagle wrote:
> On Fri, Jul 12, 2019 at 3:59 PM Harald Jensås <hjensas at redhat.com>
> wrote:
> > I've said this before, but I think we should turn this nova-less
> > around. Now with nova-less we create a bunch of servers, and write
> > up
> > the parameters file to use the deployed-server approach.
> > Effectively we
> > still neet to have the resource group in heat making a server
> > resource
> > for every server. Creating the fake server resource is fast,
> > because
> > Heat does'nt call Nova,Ironic to create any resources. But the
> > stack is
> > equally big, with a stack for every node. i.e not N=1.
> > 
> > What you are doing here, is essentially to say we don't create a
> > resource group that then creates N number of role stacks, one for
> > each
> > overcloud node. You are creating a single generic "server"
> > definition
> > per Role. So we drop the resource group and create
> > OS::Triple::{{Role}}.Server 1-time (once). To me it's backwards to
> > push
> > a large struct with properties for N=many nodes into the creation
> > of
> > that stack.
> 
> I'm not entirely following what you're saying is backwards. What I've
> proposed is that we *don't* have any node specific data in the stack.
> It sounds like you're saying the way we do it today is backwards.
> 

What I mean to say is that I think the way we are integrating nova-less 
by first deploying the servers, to then provide the data to Heat to
create the resource groups as we do today becomes backwards when your
work on N=1 is introduced.


> It's correct that what's been proposed with metalsmith currently
> still
> requires the full ResourceGroup with a member for each node. With the
> template changes I'm proposing, that wouldn't be required, so we
> could
> actually do the Heat stack first, then metalsmith.
> 

Yes, this is what I think we should do. Especially if your changes here
removes the resource group entirely. It makes more sense to create the
stack, and once that is created we can do deployment, scaling etc
without updating the stack again.

> > Currently the puppet/role-role.yaml creates all the network ports
> > etc.
> > As you only want to create it once, it instead could simply output
> > the
> > UUID of the networks+subnets. These are identical for all servers
> > in
> > the role. So we end up with a small heat stack.
> > 
> > Once the stack is created we could use that generic "server" role
> > data
> > to feed into something (ansible?, python?, mistral?) that calls
> > metalsmith to build the servers, then create ports for each server
> > in
> > neutron, one port for each network+subnet defined in the role. Then
> > feed that output into the json (hieradata) that is pushed to each
> > node
> > and used during service configuration, all the things we need to
> > configure network interfaces, /etc/hosts and so on. We need a way
> > to
> > keep track of which ports belong to wich node, but I guess
> > something
> > simple like using the node's ironic UUID in either the name,
> > description or tag field of the neutron port will work. There is
> > also
> > the extra filed in Ironic which is json type, so we could place a
> > map
> > of network->port_uuid in there as well.
> 
> It won't matter whether we do baremetal provisioning before or after
> the Heat stack. Heat won't care, as it won't have any expectation to
> create any servers or that they are already created. We can define
> where we end up calling the metalsmith piece as it should be
> independent of the Heat stack if we make these template changes.
> 

This is true. But, in your previous mail in this thread you wrote:

"""
Other points:

- Baremetal provisioning and port creation are presently handled by
Heat. With the ongoing efforts to migrate baremetal provisioning out
of Heat (nova-less deploy), I think these efforts are very
complimentary. Eventually, we get to a point where Heat is not
actually creating any other OpenStack API resources. For now, the
patches only work when using pre-provisioned nodes.
"""

IMO "baremetal provision and port creation" fit together. (I read the
above statement so as well.) Currently nova-less creates the ctlplane
port and provision the baremetal node. If we want to do both baremetal
provisioning and port creation togheter (I think this makes sense), we
have to do it after the stack has created the networks. 

What I envision is to have one method that creates all the ports,
ctlplane + composable networks in a unified way. Today these are
created differently, the ctlplane port is part of the server resource
(or metalsmith in nova-less case) and the other ports are created by
heat.

> > I think the creation of the actual Networks and Subnets can be left
> > in
> > heat, it's typically 5-6 networks and 5-6 subnets so it's not a lot
> > of
> > resources. Even in a large DCN deployment having 50-100 subnets per
> > network or even 50-100 networks I think this is'nt a problem.
> 
> Agreed, I'm not specifically proposing we move those pieces at this
> time.
> 

+1