include

Include expression allows you to add one template to another.

Variables that are transmitted as data must contain all data for both the master template and the one that is added through include.

Template templates/vlans.txt:

{% for vlan, name in vlans.items() %}
vlan {{ vlan }}
 name {{ name }}
{% endfor %}

Template templates/ospf.txt:

router ospf 1
 auto-cost reference-bandwidth 10000
{% for networks in ospf %}
 network {{ networks.network }} area {{ networks.area }}
{% endfor %}

Template templates/bgp.txt:

router bgp {{ bgp.local_as }}
{% for ibgp in bgp.ibgp_neighbors %}
 neighbor {{ ibgp }} remote-as {{ bgp.local_as }}
 neighbor {{ ibgp }} update-source {{ bgp.loopback }}
{% endfor %}
{% for ebgp in bgp.ebgp_neighbors %}
 neighbor {{ ebgp }} remote-as {{ bgp.ebgp_neighbors[ebgp] }}
{% endfor %}

Template templates/switch.txt uses created templates ospf and vlans:

{% include 'vlans.txt' %}

{% include 'ospf.txt' %}

Data file for configuration generation (data_files/switch.yml):

vlans:
  10: Marketing
  20: Voice
  30: Management
ospf:
  - network: 10.0.1.0 0.0.0.255
    area: 0
  - network: 10.0.2.0 0.0.0.255
    area: 2
  - network: 10.1.1.0 0.0.0.255
    area: 0

The result of script execution:

$ python cfg_gen.py templates/switch.txt data_files/switch.yml
vlan 10
 name Marketing
vlan 20
 name Voice
vlan 30
 name Management

router ospf 1
 auto-cost reference-bandwidth 10000
 network 10.0.1.0 0.0.0.255 area 0
 network 10.0.2.0 0.0.0.255 area 2
 network 10.1.1.0 0.0.0.255 area 0

The resulting configuration is as if lines from templates ospf.txt and vlans.txt were in switch.txt template.

Template templates/router.txt:

{% include 'ospf.txt' %}

{% include 'bgp.txt' %}

logging {{ log_server }}

In this case, in addition to include, another line in template was added to show that include expressions can be mixed with normal template.

Data file (data_files/router.yml):

ospf:
  - network: 10.0.1.0 0.0.0.255
    area: 0
  - network: 10.0.2.0 0.0.0.255
    area: 2
  - network: 10.1.1.0 0.0.0.255
    area: 0
bgp:
  local_as: 100
  loopback: lo100
  ibgp_neighbors:
    - 10.0.0.2
    - 10.0.0.3
  ebgp_neighbors:
    90.1.1.1: 500
    80.1.1.1: 600
log_server: 10.1.1.1

The result of script execution will be:

$ python cfg_gen.py templates/router.txt data_files/router.yml
router ospf 1
 auto-cost reference-bandwidth 10000
 network 10.0.1.0 0.0.0.255 area 0
 network 10.0.2.0 0.0.0.255 area 2
 network 10.1.1.0 0.0.0.255 area 0

router bgp 100
 neighbor 10.0.0.2 remote-as 100
 neighbor 10.0.0.2 update-source lo100
 neighbor 10.0.0.3 remote-as 100
 neighbor 10.0.0.3 update-source lo100
 neighbor 90.1.1.1 remote-as 500
 neighbor 80.1.1.1 remote-as 600

logging 10.1.1.1

Thanks to include, template templates/ospf.txt is used both in template templates/switch.txt and in template templates/router.txt, instead of repeating the same thing twice.