Chapter 8 Data Models and Dynamic Templates

Exact Cisco configuration commands, including syntax, nesting, and spacing, are required to develop idempotent configurations. If the spacing is off the playbook will still execute and make the changes, however during check mode or future executions of the playbook the incorrectly spaced lines of configuration will always show up as a change, even if the commands are already present on the device.

What is a Template? Ansible uses Jinja2 templates to enable dynamic expressions and access variables in the group_vars and host_vars data dictionaries. All templates are compiled on the local Linux host at run time and then deployed to the target host. This is done to minimize the amount of information that is passed to the target device allowing only what is required to execute the playbook.

Static / Explicit Statements

With network device configurations there are a lot of static configuration commands without any real valuable information that can be abstracted into a data model. Often it is desired to explicitly execute commands and not require any dynamic data from the dictionary. Many global configurations follow this pattern. Consider the following template, the first template, 01_ios_global.j2, which covers all devices, regardless of platform, and the global configuration commands we will explicitly run on each device:

* Important note *: All of the IP addresses, routes, and other “data” used in these examples are purely fictitious and not intended to function on a network. The format and syntax is correct however the IP address values have all been randomly picked using private IP addresses.

no service pad 
service tcp-keepalives-in 
service tcp-keepalives-out 
service timestamps debug datetime msec localtime 
service timestamps log datetime msec localtime 
service password-encryption 
service compress-config 
service counters max age 5 
service compress-config 
no ip bootp server 
diagnostic bootup level complete 
errdisable recovery interval 60 
aaa new-model 
clock timezone est -5 0 
clock summer-time EDT recurring 
ip arp proxy disable 
udld enable 
no ip domain-lookup 
vtp domain ayn 
vtp mode transparent 
login on-failure log 
login on-success log 
spanning-tree mode rapid-pvst 
spanning-tree extend system-id 
ip ssh version 2 
no ip forward-protocol nd 
no ip http server 
no ip http secure-server