DevOps and Middleware Engineering: Ansible Templating (Jinja2)

Ansible uses Jinja2 templating to enable dynamic expressions and access to variables. Ansible includes a lot of specialized filters and tests for templating. You can use all the standard filters and tests included in Jinja2 as well. Ansible also offers a new plugin type: Lookup Plugins.

All templating happens on the Ansible controller before the task is sent and executed on the target machine. This approach minimizes the package requirements on the target (jinja2 is only required on the controller). It also limits the amount of data Ansible passes to the target machine. Ansible parses templates on the controller and passes only the information needed for each task to the target machine, instead of passing all the data on the controller and parsing it on the target.

Get the current time

The now() Jinja2 function retrieves a Python datetime object or a string representation for the current time.

The now() function supports 2 arguments:

utc

Specify True to get the current time in UTC. Defaults to False.

fmt

Accepts a strftime string that returns a formatted date time string.

Using filters to manipulate data

Filters let you transform JSON data into YAML data, split a URL to extract the hostname, get the SHA1 hash of a string, add or multiply integers, and much more. You can use the Ansible-specific filters documented here to manipulate your data, or use any of the standard filters shipped with Jinja2 - see the list of built-in filters in the official Jinja2 template documentation. You can also use Python methods to transform data. You can create custom Ansible filters as plugins, though we generally welcome new filters into the ansible-base repo so everyone can use them.

Because templating happens on the Ansible controller, not on the target host, filters execute on the controller and transform data locally.

Handling undefined variables

Filters can help you manage missing or undefined variables by providing defaults or making some variables optional. If you configure Ansible to ignore most undefined variables, you can mark some variables as requiring values with the mandatory filter.

Providing default values

You can provide default values for variables directly in your templates using the Jinja2 ‘default’ filter. This is often a better approach than failing if a variable is not defined:

In the above example, if the variable ‘some_variable’ is not defined, Ansible uses the default value 5, rather than raising an “undefined variable” error and failing. If you are working within a role, you can also add a defaults/main.yml to define the default values for variables in your role.

Beginning in version 2.8, attempting to access an attribute of an Undefined value in Jinja will return another Undefined value, rather than throwing an error immediately. This means that you can now simply use a default with a value in a nested data structure (in other words, {{ foo.bar.baz | default('DEFAULT') }}) when you do not know if the intermediate values are defined.

If you want to use the default value when variables evaluate to false or an empty string you have to set the second parameter to true:

Making variables optional

By default Ansible requires values for all variables in a templated expression. However, you can make specific variables optional. For example, you might want to use a system default for some items and control the value for others. To make a variable optional, set the default value to the special variable omit:

- name: Touch files with an optional mode

ansible.builtin.file:

dest: "{{ item.path }}"

state: touch

mode: "{{ item.mode | default(omit) }}"

loop:

- path: /tmp/foo

- path: /tmp/bar

- path: /tmp/baz

mode: "0444"

In this example, the default mode for the files /tmp/foo and /tmp/bar is determined by the umask of the system. Ansible does not send a value for mode. Only the third file, /tmp/baz, receives the mode=0444 option.

Note

If you are “chaining” additional filters after the default(omit) filter, you should instead do something like this: "{{ foo | default(None) | some_filter or omit }}". In this example, the default None (Python null) value will cause the later filters to fail, which will trigger the or omit portion of the logic. Using omit in this manner is very specific to the later filters you are chaining though, so be prepared for some trial and error if you do this.

Defining mandatory values

If you configure Ansible to ignore undefined variables, you may want to define some values as mandatory. By default, Ansible fails if a variable in your playbook or command is undefined. You can configure Ansible to allow undefined variables by setting DEFAULT_UNDEFINED_VAR_BEHAVIOR to false. In that case, you may want to require some variables to be defined. You can do this with:

The variable value will be used as is, but the template evaluation will raise an error if it is undefined.

Defining different values for true/false/null (ternary)

You can create a test, then define one value to use when the test returns true and another when the test returns false (new in version 1.9):

{{ (status == 'needs_restart') | ternary('restart', 'continue') }}

In addition, you can define a one value to use on true, one value on false and a third value on null (new in version 2.8):

Managing data types

You might need to know, change, or set the data type on a variable. For example, a registered variable might contain a dictionary when your next task needs a list, or a user prompt might return a string when your playbook needs a boolean value. Use the type_debug, dict2items, and items2dict filters to manage data types. You can also use the data type itself to cast a value as a specific data type.

Discovering the data type

If you are unsure of the underlying Python type of a variable, you can use the type_debug filter to display it. This is useful in debugging when you need a particular type of variable:

Transforming dictionaries into lists

Use the dict2items filter to transform a dictionary into a list of items suitable for looping:

Dictionary data (before applying the dict2items filter):

tags:

Application: payment

Environment: dev

List data (after applying the dict2items filter):

- key: Application

value: payment

- key: Environment

value: dev

The dict2items filter is the reverse of the items2dict filter.

If you want to configure the names of the keys, the dict2items filter accepts 2 keyword arguments. Pass the key_name and value_name arguments to configure the names of the keys in the list output:

Dictionary data (before applying the dict2items filter):

files:

users: /etc/passwd

groups: /etc/group

List data (after applying the dict2items filter):

- file: users

path: /etc/passwd

- file: groups

path: /etc/group

Transforming lists into dictionaries

Use the items2dict filter to transform a list into a dictionary, mapping the content into key: value pairs:

List data (before applying the items2dict filter):

tags:

- key: Application

value: payment

- key: Environment

value: dev

Dictionary data (after applying the items2dict filter):

Application: payment

Environment: dev

The items2dict filter is the reverse of the dict2items filter.

Not all lists use key to designate keys and value to designate values. For example:

fruits:

- fruit: apple

color: red

- fruit: pear

color: yellow

- fruit: grapefruit

color: yellow

In this example, you must pass the key_name and value_name arguments to configure the transformation. For example:

If you do not pass these arguments, or do not pass the correct values for your list, you will see KeyError: key or KeyError: my_typo.

Forcing the data type

You can cast values as certain types. For example, if you expect the input “True” from a vars_prompt and you want Ansible to recognize it as a boolean value instead of a string:

- debug:

msg: test

when: some_string_value | bool

If you want to perform a mathematical comparison on a fact and you want Ansible to recognize it as an integer instead of a string:

- shell: echo "only on Red Hat 6, derivatives, and later"

when: ansible_facts['os_family'] == "RedHat" and ansible_facts['lsb']['major_release'] | int >= 6

New in version 1.6.

Formatting data: YAML and JSON

You can switch a data structure in a template from or to JSON or YAML format, with options for formatting, indenting, and loading data. The basic filters are occasionally useful for debugging:

For human readable output, you can use:

You can change the indentation of either format:

The to_yaml and to_nice_yaml filters use the PyYAML library which has a default 80 symbol string length limit. That causes unexpected line break after 80th symbol (if there is a space after 80th symbol) To avoid such behavior and generate long lines, use the width option. You must use a hardcoded number to define the width, instead of a construction like float("inf"), because the filter does not support proxying Python functions. For example:

If you are reading in some already formatted data:

for example:

tasks:

- name: Register JSON output as a variable

ansible.builtin.shell: cat /some/path/to/file.json

- name: Set a variable

ansible.builtin.set_fact:

myvar: "{{ result.stdout | from_json }}"

Filter to_json and Unicode support

By default to_json and to_nice_json will convert data received to ASCII, so:

will return:

'M\u00fcnchen'

To keep Unicode characters, pass the parameter ensure_ascii=False to the filter:

'München'

To parse multi-document YAML strings, the from_yaml_all filter is provided. The from_yaml_all filter will return a generator of parsed YAML documents.

for example:

tasks:

- name: Register a file content as a variable

ansible.builtin.shell: cat /some/path/to/multidoc-file.yaml

- name: Print the transformed variable

ansible.builtin.debug:

msg: '{{ item }}'

loop: '{{ result.stdout | from_yaml_all | list }}'

Combining and selecting data

You can combine data from multiple sources and types, and select values from large data structures, giving you precise control over complex data.

Combining items from multiple lists: zip and zip_longest

To get a list combining the elements of other lists use zip:

- name: Give me list combo of two lists

ansible.builtin.debug:

msg: "{{ [1,2,3,4,5] | zip(['a','b','c','d','e','f']) | list }}"

- name: Give me shortest combo of two lists

ansible.builtin.debug:

msg: "{{ [1,2,3] | zip(['a','b','c','d','e','f']) | list }}"

To always exhaust all lists use zip_longest:

- name: Give me longest combo of three lists , fill with X

ansible.builtin.debug:

msg: "{{ [1,2,3] | zip_longest(['a','b','c','d','e','f'], [21, 22, 23], fillvalue='X') | list }}"

Similarly to the output of the items2dict filter mentioned above, these filters can be used to construct a dict:

List data (before applying the zip filter):

keys_list:

- one

- two

values_list:

- apple

- orange

Dictonary data (after applying the zip filter):

one: apple

two: orange

Combining objects and subelements

The subelements filter produces a product of an object and the subelement values of that object, similar to the subelements lookup. This lets you specify individual subelements to use in a template. For example, this expression:

Data before applying the subelements filter:

users:

- name: alice

authorized:

- /tmp/alice/onekey.pub

- /tmp/alice/twokey.pub

groups:

- wheel

- docker

- name: bob

authorized:

- /tmp/bob/id_rsa.pub

groups:

- docker

Data after applying the subelements filter:

- name: alice

groups:

- wheel

- docker

authorized:

- /tmp/alice/onekey.pub

- /tmp/alice/twokey.pub

- wheel

- name: alice

groups:

- wheel

- docker

authorized:

- /tmp/alice/onekey.pub

- /tmp/alice/twokey.pub

- docker

- name: bob

authorized:

- /tmp/bob/id_rsa.pub

groups:

- docker

You can use the transformed data with loop to iterate over the same subelement for multiple objects:

- name: Set authorized ssh key, extracting just that data from 'users'

ansible.posix.authorized_key:

user: "{{ item.0.name }}"

key: "{{ lookup('file', item.1) }}"

loop: "{{ users | subelements('authorized') }}"

Combining hashes/dictionaries

The combine filter allows hashes to be merged. For example, the following would override keys in one hash:

{{ {'a':1, 'b':2} | combine({'b':3}) }}

The resulting hash would be:

{'a':1, 'b':3}

The filter can also take multiple arguments to merge:

In this case, keys in d would override those in c, which would override those in b, and so on.

The filter also accepts two optional parameters: recursive and list_merge.

recursive

Is a boolean, default to False. Should the combine recursively merge nested hashes. Note: It does not depend on the value of the hash_behaviour setting in ansible.cfg.

list_merge

Is a string, its possible values are replace (default), keep, append, prepend, append_rp or prepend_rp. It modifies the behaviour of combine when the hashes to merge contain arrays/lists.

default:

x: default

y: default

b: default

c: default

patch:

y: patch

z: patch

b: patch

If recursive=False (the default), nested hash aren’t merged:

This would result in:

y: patch

z: patch

b: patch

c: default

If recursive=True, recurse into nested hash and merge their keys:

This would result in:

x: default

y: patch

z: patch

b: patch

c: default

If list_merge='replace' (the default), arrays from the right hash will “replace” the ones in the left hash:

default:

- default

patch:

- patch

This would result in:

- patch

If list_merge='keep', arrays from the left hash will be kept:

This would result in:

- default

If list_merge='append', arrays from the right hash will be appended to the ones in the left hash:

This would result in:

- default

- patch

If list_merge='prepend', arrays from the right hash will be prepended to the ones in the left hash:

This would result in:

- patch

- default

If list_merge='append_rp', arrays from the right hash will be appended to the ones in the left hash. Elements of arrays in the left hash that are also in the corresponding array of the right hash will be removed (“rp” stands for “remove present”). Duplicate elements that aren’t in both hashes are kept:

default:

- 1

- 2

- 3

patch:

- 3

- 4

- 5

This would result in:

- 1

- 2

- 3

- 4

- 5

If list_merge='prepend_rp', the behavior is similar to the one for append_rp, but elements of arrays in the right hash are prepended:

This would result in:

- 3

- 4

- 5

- 1

- 2

recursive and list_merge can be used together:

default:

a':

x: default_value

y: default_value

list:

- default_value

- 1

- 2

- 3

patch:

a':

y: patch_value

z: patch_value

list:

- patch_value

- 3

- 4

- key: value

{{ default | combine(patch, recursive=True, list_merge='append_rp') }}

This would result in:

a':

x: default_value

y: patch_value

z: patch_value

list:

- default_value

- patch_value

- 1

- 2

- 3

- 4

- key: value

Selecting values from arrays or hashtables

The extract filter is used to map from a list of indices to a list of values from a container (hash or array):

{{ ['x','y'] | map('extract', {'x': 42, 'y': 31}) | list }}

The results of the above expressions would be:

['x', 'z']

[42, 31]

The filter can take another argument:

{{ groups['x'] | map('extract', hostvars, 'ec2_ip_address') | list }}

This takes the list of hosts in group ‘x’, looks them up in hostvars, and then looks up the ec2_ip_address of the result. The final result is a list of IP addresses for the hosts in group ‘x’.

The third argument to the filter can also be a list, for a recursive lookup inside the container:

This would return a list containing the value of b[‘a’][‘x’][‘y’].

Combining lists

This set of filters returns a list of combined lists.

permutations

To get permutations of a list:

- name: Give me largest permutations (order matters)

ansible.builtin.debug:

msg: "{{ [1,2,3,4,5] | permutations | list }}"

- name: Give me permutations of sets of three

ansible.builtin.debug:

msg: "{{ [1,2,3,4,5] | permutations(3) | list }}"

combinations

Combinations always require a set size:

- name: Give me combinations for sets of two

ansible.builtin.debug:

msg: "{{ [1,2,3,4,5] | combinations(2) | list }}"

Also see the Combining items from multiple lists: zip and zip_longest

products

The product filter returns the cartesian product of the input iterables. This is roughly equivalent to nested for-loops in a generator expression.

For example:

- name: Generate multiple hostnames

ansible.builtin.debug:

msg: "{{ ['foo', 'bar'] | product(['com']) | map('join', '.') | join(',') }}"

This would result in:

{ "msg": "foo.com,bar.com" }

Selecting JSON data: JSON queries

To select a single element or a data subset from a complex data structure in JSON format (for example, Ansible facts), use the json_query filter. The json_query filter lets you query a complex JSON structure and iterate over it using a loop structure.

Note

This filter has migrated to the community.general collection. Follow the installation instructions to install that collection.

Note

This filter is built upon jmespath, and you can use the same syntax. For examples, see jmespath examples.

Consider this data structure:

{

"domain_definition": {

"domain": {

"cluster": [

{

"name": "cluster1"

{

"name": "cluster2"

}

"server": [

{

"name": "server11",

"cluster": "cluster1",

"port": "8080"

{

"name": "server12",

"cluster": "cluster1",

"port": "8090"

{

"name": "server21",

"cluster": "cluster2",

"port": "9080"

{

"name": "server22",

"cluster": "cluster2",

"port": "9090"

}

"library": [

{

"name": "lib1",

"target": "cluster1"

{

"name": "lib2",

"target": "cluster2"

}

]

}

To extract all clusters from this structure, you can use the following query:

- name: Display all cluster names

ansible.builtin.debug:

var: item

loop: "{{ domain_definition | community.general.json_query('domain.cluster[*].name') }}"

To extract all server names:

- name: Display all server names

ansible.builtin.debug:

var: item

loop: "{{ domain_definition | community.general.json_query('domain.server[*].name') }}"

To extract ports from cluster1:

- ansible.builtin.name: Display all ports from cluster1

debug:

var: item

loop: "{{ domain_definition | community.general.json_query(server_name_cluster1_query) }}"

vars:

server_name_cluster1_query: "domain.server[?cluster=='cluster1'].port"

Note

You can use a variable to make the query more readable.

To print out the ports from cluster1 in a comma separated string:

- name: Display all ports from cluster1 as a string

ansible.builtin.debug:

msg: "{{ domain_definition | community.general.json_query('domain.server[?cluster==`cluster1`].port') | join(', ') }}"

Note

In the example above, quoting literals using backticks avoids escaping quotes and maintains readability.

You can use YAML single quote escaping:

- name: Display all ports from cluster1

ansible.builtin.debug:

var: item

loop: "{{ domain_definition | community.general.json_query('domain.server[?cluster==''cluster1''].port') }}"

Note

Escaping single quotes within single quotes in YAML is done by doubling the single quote.

To get a hash map with all ports and names of a cluster:

- name: Display all server ports and names from cluster1

ansible.builtin.debug:

var: item

loop: "{{ domain_definition | community.general.json_query(server_name_cluster1_query) }}"

vars:

server_name_cluster1_query: "domain.server[?cluster=='cluster2'].{name: name, port: port}"

Randomizing data

When you need a randomly generated value, use one of these filters.

Random MAC addresses

This filter can be used to generate a random MAC address from a string prefix.

To get a random MAC address from a string prefix starting with ‘52:54:00’:

"{{ '52:54:00' | community.general.random_mac }}"

# => '52:54:00:ef:1c:03'

Note that if anything is wrong with the prefix string, the filter will issue an error.

As of Ansible version 2.9, you can also initialize the random number generator from a seed to create random-but-idempotent MAC addresses:

"{{ '52:54:00' | community.general.random_mac(seed=inventory_hostname) }}"

Random items or numbers

The random filter in Ansible is an extension of the default Jinja2 random filter, and can be used to return a random item from a sequence of items or to generate a random number based on a range.

To get a random item from a list:

"{{ ['a','b','c'] | random }}"

# => 'c'

To get a random number between 0 and a specified number:

"{{ 60 | random }} * * * * root /script/from/cron"

# => '21 * * * * root /script/from/cron'

To get a random number from 0 to 100 but in steps of 10:

# => 70

To get a random number from 1 to 100 but in steps of 10:

# => 31

# => 51

You can initialize the random number generator from a seed to create random-but-idempotent numbers:

"{{ 60 | random(seed=inventory_hostname) }} * * * * root /script/from/cron"

Shuffling a list

The shuffle filter randomizes an existing list, giving a different order every invocation.

To get a random list from an existing list:

# => ['c','a','b']

# => ['b','c','a']

You can initialize the shuffle generator from a seed to generate a random-but-idempotent order:

# => ['b','a','c']

The shuffle filter returns a list whenever possible. If you use it with a non ‘listable’ item, the filter does nothing.

Managing list variables

You can search for the minimum or maximum value in a list, or flatten a multi-level list.

To get the minimum value from list of numbers:

To get the maximum value from a list of numbers:

Flatten a list (same thing the flatten lookup does):

Flatten only the first level of a list (akin to the items lookup):

Selecting from sets or lists (set theory)

You can select or combine items from sets or lists.

To get a unique set from a list:

# list1: [1, 2, 5, 1, 3, 4, 10]

# => [1, 2, 5, 3, 4, 10]

To get a union of two lists:

# list1: [1, 2, 5, 1, 3, 4, 10]

# list2: [1, 2, 3, 4, 5, 11, 99]

# => [1, 2, 5, 1, 3, 4, 10, 11, 99]

To get the intersection of 2 lists (unique list of all items in both):

# list1: [1, 2, 5, 3, 4, 10]

# list2: [1, 2, 3, 4, 5, 11, 99]

# => [1, 2, 5, 3, 4]

To get the difference of 2 lists (items in 1 that don’t exist in 2):

# list1: [1, 2, 5, 1, 3, 4, 10]

# list2: [1, 2, 3, 4, 5, 11, 99]

# => [10]

To get the symmetric difference of 2 lists (items exclusive to each list):

# list1: [1, 2, 5, 1, 3, 4, 10]

# list2: [1, 2, 3, 4, 5, 11, 99]

# => [10, 11, 99]

Calculating numbers (math)

You can calculate logs, powers, and roots of numbers with Ansible filters. Jinja2 provides other mathematical functions like abs() and round().

Get the logarithm (default is e):

Get the base 10 logarithm:

Give me the power of 2! (or 5):

Square root, or the 5th:

Managing network interactions

These filters help you with common network tasks.

Note

These filters have migrated to the ansible.netcommon collection. Follow the installation instructions to install that collection.

IP address filters

To test if a string is a valid IP address:

You can also require a specific IP protocol version:

IP address filter can also be used to extract specific information from an IP address. For example, to get the IP address itself from a CIDR, you can use:

Network CLI filters

To convert the output of a network device CLI command into structured JSON output, use the parse_cli filter:

The parse_cli filter will load the spec file and pass the command output through it, returning JSON output. The YAML spec file defines how to parse the CLI output.

The spec file should be valid formatted YAML. It defines how to parse the CLI output and return JSON data. Below is an example of a valid spec file that will parse the output from the show vlan command.

---

vars:

vlan:

vlan_id: "{{ item.vlan_id }}"

enabled: "{{ item.state != 'act/lshut' }}"

state: "{{ item.state }}"

keys:

vlans:

value: "{{ vlan }}"

items: "^(?P<vlan_id>\\d+)\\s+(?P<name>\\w+)\\s+(?P<state>active|act/lshut|suspended)"

state_static:

value: present

The spec file above will return a JSON data structure that is a list of hashes with the parsed VLAN information.

The same command could be parsed into a hash by using the key and values directives. Here is an example of how to parse the output into a hash value using the same show vlan command.

---

vars:

vlan:

key: "{{ item.vlan_id }}"

values:

vlan_id: "{{ item.vlan_id }}"

enabled: "{{ item.state != 'act/lshut' }}"

state: "{{ item.state }}"

keys:

vlans:

value: "{{ vlan }}"

items: "^(?P<vlan_id>\\d+)\\s+(?P<name>\\w+)\\s+(?P<state>active|act/lshut|suspended)"

state_static:

value: present

Another common use case for parsing CLI commands is to break a large command into blocks that can be parsed. This can be done using the start_block and end_block directives to break the command into blocks that can be parsed.

---

vars:

interface:

state: "{{ item[1].state }}"

mode: "{{ item[2].match[0] }}"

keys:

interfaces:

value: "{{ interface }}"

start_block: "^Ethernet.*$"

end_block: "^$"

items:

- "^(?P<name>Ethernet\\d\\/\\d*)"

- "admin state is (?P<state>.+),"

- "Port mode is (.+)"

The example above will parse the output of show interface into a list of hashes.

The network filters also support parsing the output of a CLI command using the TextFSM library. To parse the CLI output with TextFSM use the following filter:

{{ output.stdout[0] | ansible.netcommon.parse_cli_textfsm('path/to/fsm') }}

Use of the TextFSM filter requires the TextFSM library to be installed.

Network XML filters

To convert the XML output of a network device command into structured JSON output, use the parse_xml filter:

The parse_xml filter will load the spec file and pass the command output through formatted as JSON.

The spec file should be valid formatted YAML. It defines how to parse the XML output and return JSON data.

Below is an example of a valid spec file that will parse the output from the show vlan | display xml command.

---

vars:

vlan:

vlan_id: "{{ item.vlan_id }}"

desc: "{{ item.desc }}"

enabled: "{{ item.state.get('inactive') != 'inactive' }}"

state: "{% if item.state.get('inactive') == 'inactive'%} inactive {% else %} active {% endif %}"

keys:

vlans:

value: "{{ vlan }}"

top: configuration/vlans/vlan

items:

vlan_id: vlan-id

desc: description

state: ".[@inactive='inactive']"

The spec file above will return a JSON data structure that is a list of hashes with the parsed VLAN information.

The same command could be parsed into a hash by using the key and values directives. Here is an example of how to parse the output into a hash value using the same show vlan | display xml command.

---

vars:

vlan:

key: "{{ item.vlan_id }}"

values:

vlan_id: "{{ item.vlan_id }}"

desc: "{{ item.desc }}"

enabled: "{{ item.state.get('inactive') != 'inactive' }}"

state: "{% if item.state.get('inactive') == 'inactive'%} inactive {% else %} active {% endif %}"

keys:

vlans:

value: "{{ vlan }}"

top: configuration/vlans/vlan

items:

vlan_id: vlan-id

desc: description

state: ".[@inactive='inactive']"

The value of top is the XPath relative to the XML root node. In the example XML output given below, the value of top is configuration/vlans/vlan, which is an XPath expression relative to the root node (<rpc-reply>). configuration in the value of top is the outer most container node, and vlan is the inner-most container node.

items is a dictionary of key-value pairs that map user-defined names to XPath expressions that select elements. The Xpath expression is relative to the value of the XPath value contained in top. For example, the vlan_id in the spec file is a user defined name and its value vlan-id is the relative to the value of XPath in top

Attributes of XML tags can be extracted using XPath expressions. The value of state in the spec is an XPath expression used to get the attributes of the vlan tag in output XML.:

<rpc-reply>

<vlans>

<vlan-id>200</vlan-id>

</vlan>

</vlans>

</configuration>

</rpc-reply>

Network VLAN filters

Use the vlan_parser filter to transform an unsorted list of VLAN integers into a sorted string list of integers according to IOS-like VLAN list rules. This list has the following properties:

Vlans are listed in ascending order.

Three or more consecutive VLANs are listed with a dash.

The first line of the list can be first_line_len characters long.

Subsequent list lines can be other_line_len characters.

To sort a VLAN list:

{{ [3003, 3004, 3005, 100, 1688, 3002, 3999] | ansible.netcommon.vlan_parser }}

This example renders the following sorted list:

['100,1688,3002-3005,3999']

Another example Jinja template:

{% set parsed_vlans = vlans | ansible.netcommon.vlan_parser %}

switchport trunk allowed vlan {{ parsed_vlans[0] }}

{% for i in range (1, parsed_vlans | count) %}

switchport trunk allowed vlan add {{ parsed_vlans[i] }}

This allows for dynamic generation of VLAN lists on a Cisco IOS tagged interface. You can store an exhaustive raw list of the exact VLANs required for an interface and then compare that to the parsed IOS output that would actually be generated for the configuration.

Encrypting and checksumming strings and passwords

To get the sha1 hash of a string:

To get the md5 hash of a string:

Get a string checksum:

Other hashes (platform dependent):

To get a sha512 password hash (random salt):

To get a sha256 password hash with a specific salt:

An idempotent method to generate unique hashes per system is to use a salt that is consistent between runs:

{{ 'secretpassword' | password_hash('sha512', 65534 | random(seed=inventory_hostname) | string) }}

Hash types available depend on the master system running Ansible, ‘hash’ depends on hashlib, password_hash depends on passlib (https://passlib.readthedocs.io/en/stable/lib/passlib.hash.html).

Some hash types allow providing a rounds parameter:

{{ 'secretpassword' | password_hash('sha256', 'mysecretsalt', rounds=10000) }}

Manipulating text

Several filters work with text, including URLs, file names, and path names.

Adding comments to files

The comment filter lets you create comments in a file from text in a template, with a variety of comment styles. By default Ansible uses # to start a comment line and adds a blank comment line above and below your comment text. For example the following:

produces this output:

# Plain style (default)

Ansible offers styles for comments in C (//...), C block (/*...*/), Erlang (%...) and XML ():

You can define a custom comment character. This filter:

produces:

! My Special Case

You can fully customize the comment style:

{{ "Custom style" | comment('plain', prefix='#######\n#', postfix='#\n#######\n ###\n #') }}

That creates the following output:

#######

# Custom style

#######

###

The filter can also be applied to any Ansible variable. For example to make the output of the ansible_managed variable more readable, we can change the definition in the ansible.cfg file to this:

[defaults]

ansible_managed = This file is managed by Ansible.%n

date: %Y-%m-%d %H:%M:%S

user: {uid}

host: {host}

and then use the variable with the comment filter:

which produces this output:

# This file is managed by Ansible.

# template: /home/ansible/env/dev/ansible_managed/roles/role1/templates/test.j2

# date: 2015-09-10 11:02:58

# user: ansible

# host: myhost

Splitting URLs

The urlsplit filter extracts the fragment, hostname, netloc, password, path, port, query, scheme, and username from an URL. With no arguments, returns a dictionary of all the fields:

{{ "http://user:password@www.acme.com:9000/dir/index.html?query=term#fragment" | urlsplit('hostname') }}

# => 'www.acme.com'

{{ "http://user:password@www.acme.com:9000/dir/index.html?query=term#fragment" | urlsplit('netloc') }}

# => 'user:password@www.acme.com:9000'

{{ "http://user:password@www.acme.com:9000/dir/index.html?query=term#fragment" | urlsplit('username') }}

# => 'user'

{{ "http://user:password@www.acme.com:9000/dir/index.html?query=term#fragment" | urlsplit('password') }}

# => 'password'

{{ "http://user:password@www.acme.com:9000/dir/index.html?query=term#fragment" | urlsplit('path') }}

# => '/dir/index.html'

{{ "http://user:password@www.acme.com:9000/dir/index.html?query=term#fragment" | urlsplit('port') }}

# => '9000'

{{ "http://user:password@www.acme.com:9000/dir/index.html?query=term#fragment" | urlsplit('scheme') }}

# => 'http'

{{ "http://user:password@www.acme.com:9000/dir/index.html?query=term#fragment" | urlsplit('query') }}

# => 'query=term'

{{ "http://user:password@www.acme.com:9000/dir/index.html?query=term#fragment" | urlsplit('fragment') }}

# => 'fragment'

{{ "http://user:password@www.acme.com:9000/dir/index.html?query=term#fragment" | urlsplit }}

# =>

# {

# "fragment": "fragment",

# "hostname": "www.acme.com",

# "netloc": "user:password@www.acme.com:9000",

# "password": "password",

# "path": "/dir/index.html",

# "port": 9000,

# "query": "query=term",

# "scheme": "http",

# "username": "user"

# }

Searching strings with regular expressions

To search a string with a regex, use the “regex_search” filter:

# search for "foo" in "foobar"

# will return empty if it cannot find a match

# case insensitive search in multiline mode

{{ 'foo\nBAR' | regex_search("^bar", multiline=True, ignorecase=True) }}

To search for all occurrences of regex matches, use the “regex_findall” filter:

# Return a list of all IPv4 addresses in the string

{{ 'Some DNS servers are 8.8.8.8 and 8.8.4.4' | regex_findall('\\b(?:[0-9]{1,3}\\.){3}[0-9]{1,3}\\b') }}

To replace text in a string with regex, use the “regex_replace” filter:

# convert "ansible" to "able"

# convert "foobar" to "bar"

# convert "localhost:80" to "localhost, 80" using named groups

{{ 'localhost:80' | regex_replace('^(?P<host>.+):(?P<port>\\d+)$', '\\g<host>, \\g<port>') }}

# convert "localhost:80" to "localhost"

# change a multiline string

Note

If you want to match the whole string and you are using * make sure to always wraparound your regular expression with the start/end anchors. For example ^(.*)$ will always match only one result, while (.*) on some Python versions will match the whole string and an empty string at the end, which means it will make two replacements:

# add "https://" prefix to each item in a list

GOOD:

{{ hosts | map('regex_replace', '^(.*)$', 'https://\\1') | list }}

BAD:

# append ':80' to each item in a list

GOOD:

BAD:

Note

Prior to ansible 2.0, if “regex_replace” filter was used with variables inside YAML arguments (as opposed to simpler ‘key=value’ arguments), then you needed to escape backreferences (for example, \\1) with 4 backslashes (\\\\) instead of 2 (\\).

To escape special characters within a standard Python regex, use the “regex_escape” filter (using the default re_type=’python’ option):

# convert '^f.*o(.*)$' to '\^f\.\*o$\.\*$\$'

To escape special characters within a POSIX basic regex, use the “regex_escape” filter with the re_type=’posix_basic’ option:

# convert '^f.*o(.*)$' to '\^f\.\*o(\.\*)\$'

Managing file names and path names

To get the last name of a file path, like ‘foo.txt’ out of ‘/etc/asdf/foo.txt’:

To get the last name of a windows style file path (new in version 2.0):

To separate the windows drive letter from the rest of a file path (new in version 2.0):

To get only the windows drive letter:

To get the rest of the path without the drive letter:

To get the directory from a path:

To get the directory from a windows path (new version 2.0):

To expand a path containing a tilde (~) character (new in version 1.5):

To expand a path containing environment variables:

Note

expandvars expands local variables; using it on remote paths can lead to errors.

To get the real path of a link (new in version 1.8):

To get the relative path of a link, from a start point (new in version 1.7):

To get the root and extension of a path or file name (new in version 2.0):

# with path == 'nginx.conf' the return would be ('nginx', '.conf')

The splitext filter returns a string. The individual components can be accessed by using the first and last filters:

# with path == 'nginx.conf' the return would be 'nginx'

# with path == 'nginx.conf' the return would be 'conf'

To join one or more path components:

New in version 2.10.

Manipulating strings

To add quotes for shell usage:

- name: Run a shell command

ansible.builtin.shell: echo {{ string_value | quote }}

To concatenate a list into a string:

To work with Base64 encoded strings:

As of version 2.6, you can define the type of encoding to use, the default is utf-8:

Note

The string filter is only required for Python 2 and ensures that text to encode is a unicode string. Without that filter before b64encode the wrong value will be encoded.

Managing UUIDs

To create a namespaced UUIDv5:

{{ string | to_uuid(namespace='11111111-2222-3333-4444-555555555555') }}

New in version 2.10.

To create a namespaced UUIDv5 using the default Ansible namespace ‘361E6D51-FAEC-444A-9079-341386DA8E2E’:

New in version 1.9.

To make use of one attribute from each item in a list of complex variables, use the Jinja2 map filter:

# get a comma-separated list of the mount points (for example, "/,/mnt/stuff") on a host

Handling dates and times

To get a date object from a string use the to_datetime filter:

# Get total amount of seconds between two dates. Default date format is %Y-%m-%d %H:%M:%S but you can pass your own format

{{ (("2016-08-14 20:00:12" | to_datetime) - ("2015-12-25" | to_datetime('%Y-%m-%d'))).total_seconds() }}

# Get remaining seconds after delta has been calculated. NOTE: This does NOT convert years, days, hours, and so on to seconds. For that, use total_seconds()

{{ (("2016-08-14 20:00:12" | to_datetime) - ("2016-08-14 18:00:00" | to_datetime)).seconds }}

# This expression evaluates to "12" and not "132". Delta is 2 hours, 12 seconds

# get amount of days between two dates. This returns only number of days and discards remaining hours, minutes, and seconds

{{ (("2016-08-14 20:00:12" | to_datetime) - ("2015-12-25" | to_datetime('%Y-%m-%d'))).days }}

New in version 2.4.

To format a date using a string (like with the shell date command), use the “strftime” filter:

# Display year-month-day

# Display hour:min:sec

# Use ansible_date_time.epoch fact

# Use arbitrary epoch value

{{ '%Y-%m-%d' | strftime(0) }} # => 1970-01-01

{{ '%Y-%m-%d' | strftime(1441357287) }} # => 2015-09-04

Note

To get all string possibilities, check https://docs.python.org/3/library/time.html#time.strftime

Getting Kubernetes resource names

Note

These filters have migrated to the community.kubernetes collection. Follow the installation instructions to install that collection.

Use the “k8s_config_resource_name” filter to obtain the name of a Kubernetes ConfigMap or Secret, including its hash:

{{ configmap_resource_definition | community.kubernetes.k8s_config_resource_name }}

This can then be used to reference hashes in Pod specifications:

my_secret:

kind: Secret

deployment_resource:

kind: Deployment

spec:

template:

spec:

containers:

- envFrom:

- secretRef:

DevOps and Middleware Engineering

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Saturday, 20 February 2021

Ansible Templating (Jinja2) - Using filters to manipulate data

Handling undefined variables

Defining different values for true/false/null (ternary)

Managing data types

Formatting data: YAML and JSON

Selecting JSON data: JSON queries

Randomizing data

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