Custom Configuration Templates¶

You can build complex labs with functionality that is not yet part of netlab with the custom configuration templates that can be deployed with netlab config, netlab initial or netlab up commands. The custom configuration templates could be stored in the lab topology directory, the user’s defaults directory, or within the netlab package. See Finding Custom Configuration Templates for more details.

For a one-off deployment of custom configuration templates, use the netlab config command. To make the deployment of custom configuration template(s) part of a regular lab initialization process[1], use config group- or node attribute that can specify either a single template or a list of templates.

For example, to deploy the ospf-anycast-loopback.j2 template on members of the anycast group and mpls-ldp.j2 on all devices in your lab during the netlab up process, use the following topology file:

defaults:
  device: iosv

groups:
  anycast:
    members: [ a1, a2, a3 ]
    config: [ ospf-anycast-loopback.j2 ]
  all:
    config: [ mpls-ldp.j2 ]

nodes: [ l1, l2, l3, s1, a1, a2, a3 ]

Tip

‌config attributes from multiple overlapping groups (anycast and all in the above example) are merged on nodes that belong to multiple groups.

The config parameter can also be specified on individual nodes, for example:

defaults:
  device: cumulus

module: [ ospf ]

nodes:
  s1:
  s2:
  s3:
    config: [ something-special.j2 ]

links: [ s1-s2, s2-s3 ]

Tip

Node config attributes are merged with the group ‌config attributes. Plugins might append additional items to the node ‌config attributes.

Warning

netlab sorts custom configuration templates in the order specified in groups and nodes to speed up their deployment. Specifying custom: [ a,b ] on one node and custom: [ b,a ] on another will result in a sorting loop and a fatal error.

Custom Configuration Templates in Hierarchical Groups¶

Custom configuration templates for individual nodes are built from configuration templates of all parent groups (starting with the least-specific parent group) plus node configuration templates. When using the following topology file…

nodes:
  a:
    config: [ a ]
  b:
  c:
  d:
  e:
    config: [ e ]
  f:

groups:
  g1: [ a,b ]
  g2:
    members: [ d,g1,g3 ]
    config: [ g2a, g2b ]
  g3:
    members: [ e ]
    config: [ g3 ]

… individual nodes get the following configuration templates:

node	template
a	g2a, g2b (from g2 via g1), a (from a)
b	g2a, g2b (from g2 via g1)
c	none (it’s not a member of any group)
d	g2a, g2b (from g2)
e	g2a, g2b (from g2 via g3), g3 (from g3)
f	none (it’s not a member of any group)

If you want to remove one or more templates specified by parent groups from a node or a group, use -x to remove a specific parent template from the list or - to remove all parent templates, for example:

nodes:
  a:
    config: [ -g2b, a ]
  b:
    config: [ -, b ]
  c:
  d:
  e:
    config: [ -g1, e ]
  f:

groups:
  g1: [ a,b ]
  g2:
    members: [ d,g1,g3 ]
    config: [ g2a, g2b ]
  g3:
    members: [ e ]
    config: [ g3 ]

The following configuration templates would be applied to individual nodes in the above lab topology:

node	template
a	g2a (from g2 via g1, g2b removed), a (from a)
b	all parent templates removed, b (from b).
c	none (it’s not a member of any group)
d	g2a, g2b (from g2)
e	g2a, g2b (from g2 via g3), g3 (from g3), -g1 is ignored, e (from e)
f	none (it’s not a member of any group)