[ClusterLabs] Coming in Pacemaker 1.1.17: container bundles

[Ken Gaillot]

On 04/13/2017 07:04 AM, Jan Pokorný wrote:
> On 03/04/17 09:47 -0500, Ken Gaillot wrote:
>> On 04/03/2017 02:12 AM, Ulrich Windl wrote:
>>>>>> Ken Gaillot <kgaillot at redhat.com> schrieb am 01.04.2017 um 00:43 in Nachricht
>>> <981d420d-73b2-3f24-a67c-e9c66dafb48f at redhat.com>:
>>>
>>> [...]
>>>> Pacemaker 1.1.17 introduces a new type of resource: the "bundle". A
>>>> bundle is a single resource specifying the Docker settings, networking
>>>> requirements, and storage requirements for any number of containers
>>>> generated from the same Docker image.
>>>
>>> I wonder: Is a "bundle" just a kind of special "group template"? It
>>> looks as if I could do it with a group also, but would have to
>>> write a bite more to get it configured. Did I miss something?
>>
>> With a group, you could reproduce most of this functionality, though it
>> would be more verbose: you'd need to configure ocf:heartbeat:docker,
>> ocf:heartbeat:IPaddr2, and ocf:pacemaker:remote resources, plus a
>> primitive for your service, as well as constraints that restrict the
>> primitive to the guest node and prevent any other resource from running
>> on the guest node.
>>
>> However, this can do something that a group can't: launch multiple
>> instances of a single container image, while associating floating IPs
>> and storage mappings specific to each replica. This puts it somewhere
>> between a group and a specialized form of clone.
> 
> In that case, wouldn't it be more systemic to factor any generic
> clone/master-like controls (replicas, replicas-per-host, masters) out
> of <docker> so it can be reused seemlessly when switching to other
> possible containerization backends in the future?

We did consider that. It's not clear how much of the functionality (or
terminology) will be applicable to other technologies (currently known
and potential future ones). We decided that it would be cleaner to
duplicate those fields in other technology tags than to have them not
work for certain technologies.

> 
>> Also, it will be shown differently in the cluster status, which is
>> helpful.