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Hi Heat team,

A question inline.

Best regards,
Hongbin

> -----Original Message-----
> From: Steven Hardy [mailto:shardy at redhat.com]
> Sent: March-03-16 3:57 AM
> To: OpenStack Development Mailing List (not for usage questions)
> Subject: Re: [openstack-dev] [magnum][heat] spawn a group of nodes on
> different availability zones
> 
> On Wed, Mar 02, 2016 at 05:40:20PM -0500, Zane Bitter wrote:
> > On 02/03/16 05:50, Mathieu Velten wrote:
> > >Hi all,
> > >
> > >I am looking at a way to spawn nodes in different specified
> > >availability zones when deploying a cluster with Magnum.
> > >
> > >Currently Magnum directly uses predefined Heat templates with Heat
> > >parameters to handle configuration.
> > >I tried to reach my goal by sticking to this model, however I
> > >couldn't find a suitable Heat construct that would allow that.
> > >
> > >Here are the details of my investigation :
> > >- OS::Heat::ResourceGroup doesn't allow to specify a list as a
> > >variable that would be iterated over, so we would need one
> > >ResourceGroup by AZ
> > >- OS::Nova::ServerGroup only allows restriction at the hypervisor
> > >level
> > >- OS::Heat::InstanceGroup has an AZs parameter but it is marked
> > >unimplemented , and is CFN specific.
> > >- OS::Nova::HostAggregate only seems to allow adding some metadatas
> > >to a group of hosts in a defined availability zone
> > >- repeat function only works inside the properties section of a
> > >resource and can't be used at the resource level itself, hence
> > >something like that is not allowed :
> > >
> > >resources:
> > >   repeat:
> > >     for_each:
> > >       <%az%>: { get_param: availability_zones }
> > >     template:
> > >       rg-<%az%>:
> > >         type: OS::Heat::ResourceGroup
> > >         properties:
> > >           count: 2
> > >           resource_def:
> > >             type: hot_single_server.yaml
> > >             properties:
> > >               availability_zone: <%az%>
> > >
> > >
> > >The only possibility that I see is generating a ResourceGroup by AZ,
> > >but it would induce some big changes in Magnum to handle
> > >modification/generation of templates.
> > >
> > >Any ideas ?
> >
> > This is a long-standing missing feature in Heat. There are two
> > blueprints for this (I'm not sure why):
> >
> > https://blueprints.launchpad.net/heat/+spec/autoscaling-
> availabilityzo
> > nes-impl
> > https://blueprints.launchpad.net/heat/+spec/implement-
> autoscalinggroup
> > -availabilityzones
> >
> > The latter had a spec with quite a lot of discussion:
> >
> > https://review.openstack.org/#/c/105907
> >
> > And even an attempted implementation:
> >
> > https://review.openstack.org/#/c/116139/
> >
> > which was making some progress but is long out of date and would need
> > serious work to rebase. The good news is that some of the changes I
> > made in Liberty like https://review.openstack.org/#/c/213555/ should
> > hopefully make it simpler.
> >
> > All of which is to say, if you want to help then I think it would be
> > totally do-able to land support for this relatively early in Newton :)
> >
> >
> > Failing that, the only think I can think to try is something I am
> > pretty sure won't work: a ResourceGroup with something like:
> >
> >   availability_zone: {get_param: [AZ_map, "%i"]}
> >
> > where AZ_map looks something like {"0": "az-1", "1": "az-2", "2":
> > "az-1", ...} and you're using the member index to pick out the AZ to
> > use from the parameter. I don't think that works (if "%i" is resolved
> > after get_param then it won't, and I suspect that's the case) but
> it's
> > worth a try if you need a solution in Mitaka.
> 
> Yeah, this won't work if you attempt to do the map/index lookup in the
> top-level template where the ResourceGroup is defined, but it *does*
> work if you pass both the map and the index into the nested stack, e.g
> something like this (untested):
> 
> $ cat rg_az_map.yaml
> heat_template_version: 2015-04-30
> 
> parameters:
>   az_map:
>     type: json
>     default:
>       '0': az1
>       '1': az2
> 
> resources:
>  AGroup:
>     type: OS::Heat::ResourceGroup
>     properties:
>       count: 2
>       resource_def:
>         type: server_mapped_az.yaml
>         properties:
>           availability_zone_map: {get_param: az_map}
>           index: '%index%'
> 
> $ cat server_mapped_az.yaml
> heat_template_version: 2015-04-30
> 
> parameters:
>   availability_zone_map:
>     type: json
>   index:
>     type: string
> 
> resources:
>  server:
>     type: OS::Nova::Server
>     properties:
>       image: the_image
>       flavor: m1.foo
>       availability_zone: {get_param: [availability_zone_map, {get_param:
> index}]}

This is nice. It seems to address our heterogeneity requirement at *deploy* time. However, I wonder what is the runtime behavior. For example, I deploy a stack by:
$ heat stack-create -f rg_az_map.yaml -P az_map='{"0":"az1","1":"az2"}'

Then, I want to remove a sever by:
$ heat stack-update -f rg_az_map.yaml -P az_map='{"0":"az1"}'

Will Heat remove resources in index "1" only (with resources in index "0" untouched)? Also, I wonder if we can dynamically add resources (with existing resources untouched). For example, add a server by:
$ heat stack-update -f rg_az_map.yaml -P az_map='{"0":"az1","1":"az2","2":"az3"}'

In addition, I want to point out that spreading the availability zones is not the only use case. Magnum has generic use cases to manage heterogeneous set of resources. For example:
$ heat stack-create -f rg_az_map.yaml -P az_map='{"resource_gorup_1":{"availability_zone":"az1","count":"2","flavor":"m1.foo",...},"resource_gorup_2":{"availability_zone":"az2","count":"3","flavor":"m2.foo",...},...}"

Is it a reasonable to expect Heat to support that?

> 
> FWIW we already use this technique in some TripleO templates, and it
> works pretty well.
> 
> https://github.com/openstack/tripleo-heat-
> templates/blob/master/network/ports/external_from_pool.yaml#L35
> 
> Steve
> 
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