Composite topologies

[jbemmel]

Currently topologies are flat, consisting of a single level of nodes and links. However, some topologies have a regular structure that is best expressed as a multi-level topology:

nodes:
 superspine1:
 superspine2:
 pod1:
  topology: pod.yml
  device: srlinux
 pod2:
  topology: pod.yml
  device: ceos

links:
- [ superspine1, pod1.spine1 ]
- [ superspine1, pod1.spine2 ]
- [ superspine1, pod2.spine1 ]
- [ superspine1, pod2.spine2 ]
- ... etc

pod.yml:
nodes:
 spine1:
 spine2:
 ... etc

'pod.yml' need not be a separate YAML file, there could be a way to embed multiple nodes+links structures in a single file

[ipspace]

Implementing included topology files is a no-brainer. Requires a bit of renaming within the included data structure, but not more.

The interesting thing is "how do we do it within a single topology file". We're almost there with groups, so we could just reuse groups, adding device, nodes and links attributes to individual groups.

Alternatively, we could add named sub-topologies (or whatever you want to call them) as top-level elements in the topology file (probably better than messing with groups), and include them in nodes somehow. Any idea how you'd like that glue to look like?

[jbemmel]

I would make sub-topologies an optional add-on, leaving groups as they are.

For example:

sub-topologies:
 pod:
  defaults:
   device: srlinux
  nodes:
   a:
   b:
   c:
  links: [ a-b, b-c, c-a ]

nodes:
 pod1:
  topology: pod
 pod2:
  topology: pod

links: [ pod1.a, pod2.b ]

[jbemmel]

'topology' could also reference a separate YAML file, instead of a sub-topology within the same file

Node names in sub topologies would be implied ( like "pod1.a" ), and you could even have sub-topologies within sub-topologies, etc.

[ipspace]

What if we use topology within a pseudo-node to point to another top-level element in the same topology file and include to point to an include file?

And yes, collecting sub-topologies under a well-known top-level element makes more sense than trying to guess what they are. I just don't like sub-topologies for whatever reason. Any other ideas?

[jbemmel]

fantastic_beasts_and_where_to_find_them:
...

:)

I don't know, I'm sure we'll think of something

[ipspace]

Love the idea, but it's a bit long. Maybe

every_flavor_beans:
...

😆

[ipspace]

Implemented in #768