[openstack-dev] [fuel] NodeGroups vs network-templates and static routes

Andrew Woodward xarses at gmail.com
Thu Jul 16 19:53:03 UTC 2015

In 6.0 we added nodegroups as part of the multiple-cluster-networks
features. With these you can add additional sets of networks with so that
the nodes can exist on different network segments. When these are used you
will also need to set the gateway for each of your networks. When you do
this, you get routes set up between the matching network names across the

For example network.yaml that looks like (shortened)

- cidr:
  group_id: 2
  id: 6
- cidr:
  group_id: 3
  id: 9

Will result in mappings like this in a nodes yaml (in nodegroup 2)

      - net:

With the introduction of templates we may no longer need nodegroups. They
served two functions. 1) They allowed us to create additional networks. 2)
They created additional routes between networks of the same name. Comparing
with what is in templates, #1 is taken care of, but what about #2? I think
that we need the routes configured anyway. Nodes with the same network role
should have a route for it when it crosses network segments.

This would have traditionally been separated by nodegroups. but it now can
be coded with templates. In this case (such as the yaml above) we must have
routes for the nodes to communicate on the correct interface. Since we need
code for routes between segments of the same network role, it might behoove
ourselves to compute (maybe not use when they are the local interface).
This serves two functions, it allows us to visualize the routing topology
instead of just relying on the default route. Secondly when we get to using
a routing protocol it gives us the data necessary to validate the routing
protocol with what we expected.

Regardless of computing all the routes, we need to compute same role, but
multi-segement routes. In this case I see that nodegroups becomes
redundant. It's only value is that it may be a simpler interface then
templates but it imposes the old network topology which I could see people
wanting to get away from.


Andrew Woodward


Fuel Community Ambassador

Ceph Community
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