8.8 KiB
CLI Template Directives
Note network_template lookup plugin is deprecated in v2.7.3 and will be removed
in version v2.7.7 i.e, four releases from the deprecation version.
The network_template module supports a number of keyword based objectives that
handle how to process the template. Templates are broken up into a series
of blocks that process lines. Blocks are logical groups that have a common
set of properties in common.
Blocks can also include other template files and are processed in the same manner as lines. See includes below for a description on how to use the include directive.
The template module works by processing the lines directives in sequential order. The module will attempt to template each line in the lines directive and, if successful, add the line to the final output. Values used for variable substitution come from the host facts. If the line could not be successfully templated, the line is skipped and a warning message is displayed that the line could not be templated.
There are additional directives that can be combined to support looping over lists and hashes as well as applying conditional statements to blocks, lines and includes.
name
Entries in the template may contain a name field. The name field
is used to provide a description of the entry. It is also used to provide
feedback when processing the template to indicate when an entry is
skipped or fails.
lines
The lines directive provides an ordered list of statements to attempt
to template. Each entry in the lines directive will be evaluated for
variable substitution. If the entry can be successfully templated, then the
output will be added to the final set of entries. If the entry cannot be
successfully templated, then the entry is ignored (skipped) and a warning
message is provided. If the entry in the lines directive contains
only static text (no variables), then the line will always be processed.
The lines directive also supports standard Jinja2 filters as well as any
Ansible specific Jinja2 filters. For example, lets assume we want to add a
default value if a more specific value was not assigned by a fact.
- name: render the system hostname
lines:
- "hostname {{ hostname | default(inventory_hostname_short }}"
block
A group of lines directives can be combined into a block
directive. These block directives are used to apply a common set of
values to one or more lines or includes entries.
For instance, a block directive that contains one or more lines
entries could be use the same set of loop values or have a
common when conditional statement applied to them.
include
Sometimes it is advantageous to break up templates into separate files and
combine them. The include directive will instruct the current template
to load another template file and process it.
The include directive also supports variable substitution for the
provided file name and can be processed with the loop and when
directives.
when
The when directive allows for conditional statements to be applied to
a set of lines, a block and/or the include directive. The
when statement is evaluated prior to processing the statements and if
the condition is true, the statements will attempt to be templated. If the
statement is false, the statements are skipped and a message returned.
loop
Depending on the input facts, sometimes it is necessary to iterate over a
set of statements. The loop directive allows the same set of statements
to be processed in such a manner. The loop directive takes, as input,
the name of a fact that is either a list or a hash and iterates over the
statements for each entry.
When the provided fact is a list of items, the value will be assigned to a
variable called item and can be referenced by the statements.
When the provided fact is a hash of items, the hash key will be assigned to
the item.key variable and the hash value will be assigned to the
item.value variable. Both can then be referenced by the statements.
loop_control
The loop_control directive allows the template to configure aspects
related to how loops are process. This directive provides a set of suboptions
to configure how loops are processed.
loop_var
The loop_var directive allows the template to override the default
variable name item. This is useful when handling nested loops such
that both inner and outer loops values can be accessed.
When setting the loop_var to some string, the string will replace
item as the variable name used to access the values.
For example, lets assume instead of using item, we want to use a different variable name such as entry:
- name: render entries
lines:
- "hostname {{ entry.hostname }}"
- "domain-name {{ entry.domain_name }}"
loop: "{{ system }}"
loop_control:
loop_var: entry
join
When building template statements that include optional values for
configuration, the join directive can be useful. The join
directive instructs the template to combine the templated lines together
into a single string to insert into the configuration.
For example, lets assume there is a need to add the following statement to the configuration:
ip domain-name ansible.com vrf management
ip domain-name redhat.com
To support templating the above lines, the facts might include the domain-name and the vrf name values. Here is the example facts:
---
system:
- domain_name: ansible.com
vrf: management
- domain_name redhat.com
And the template statement would be the following:
- name: render domain-name
lines:
- "ip domain-name {{ item.domain_name }}"
- "vrf {{ item.vrf }}"
loop: "{{ system }}"
join: yes
When this entry is processed, the first iteration will successfully template
both lines and add ip domain-name ansible.com vrf management to the
output.
When the second entry is processed, the first line will be successfully
templated but since there is no management key, the second line will return a
null value. The final line added to the configuration will be ip domain-name redhat.com.
If the join directive had been omitted, then the final set of
configuration statements would be as follows:
ip domain-name ansible.com
vrf management
ip domain-name redhat.com
join_delimiter
When the join delimiter is used, the templated values are combined into a
single string that is added to the final output. The lines are joined using a
space. The delimiting character used when processing the join can be
modified using join_delimiter directive.
Here is an example of using the this directive. Take the following entry:
- name: render domain-name
lines:
- "ip domain-name {{ item.domain_name }}"
- "vrf {{ item.vrf }}"
loop: "{{ system }}"
join: yes
join_delimiter: ,
When the preceding statements are processed, the final output would be (assuming all variables are provided):
ip domain-name ansible.com,vrf management
ip domain-name redhat.com
indent
The indent directive is used to add one or more leading spaces to the
final templated statement. It can be used to recreated a structured
configuration file.
Take the following template entry as an example:
- name: render the interface context
lines: "interface Ethernet0/1"
- name: render the interface configuration
lines:
- "ip address 192.168.10.1/24"
- "no shutdown"
- "description this is an example"
indent: 3
- name: render the interface context
lines: "!"
Then the statements above are processed, the output will look like the following:
interface Ethernet0/1
ip address 192.168.10.1/24
no shutdown
description this is an example
!
required
The required directive specifies that all of the statements must be
templated otherwise a failure is generated. Essentially it is a way to
make certain that the variables are defined.
For example, take the following:
- name: render router ospf context
lines:
- "router ospf {{ process_id }}"
required: yes
When the above is processed, if the variable process_id is not present,
then the statement cannot be templated. Since the required directive
is set to true, the statement will cause the template to generate a failure
message.
missing_key
By default, when statements are processed and a variable is undefined, the module will simply display a warning message to the screen. In some cases, it is desired to either suppress warning messages on a missing key or to force the module to fail on a missing key.
To change the default behaviour, use the missing_key directive. This
directive accepts one of three choices:
ignorewarn(default)fail
The value of this directive will instruct the template how to handle any condition where the desired variable is undefined.