Loops

Sometimes you want to repeat a task multiple times. In computer programming, this is called a loop. Common Ansible loops include changing ownership on several files and/or directories with the file module, creating multiple users with the user module, and repeating a polling step until a certain result is reached. Ansible offers two keywords for creating loops: loop and with_<lookup>.

• Comparing loop and with_*
• Standard loops
  • Iterating over a simple list
  • Iterating over a list of hashes
  • Iterating over a dictionary
• Registering variables with a loop
• Complex loops
  • Iterating over nested lists
  • Retrying a task until a condition is met
  • Looping over inventory
• Ensuring list input for loop: query vs. lookup
• Adding controls to loops
  • Limiting loop output with label
  • Pausing within a loop
  • Tracking progress through a loop with index_var
  • Defining inner and outer variable names with loop_var
  • Extended loop variables
  • Accessing the name of your loop_var
• Migrating from with_X to loop
  • with_list
  • with_items
  • with_indexed_items
  • with_flattened
  • with_together
  • with_dict
  • with_sequence
  • with_subelements
  • with_nested/with_cartesian
  • with_random_choice

Comparing loop and with_*

• The with_<lookup> keywords rely on Lookup Plugins - even items is a lookup.
• The loop keyword is equivalent to with_list, and is the best choice for simple loops.
• The loop keyword will not accept a string as input, see Ensuring list input for loop: query vs. lookup.
• Generally speaking, any use of with_* covered in Migrating from with_X to loop can be updated to use loop.
• Be careful when changing with_items to loop, as with_items performed implicit single-level flattening. You may need to use flatten(1) with loop to match the exact outcome. For example, to get the same output as:

with_items:
  - 1
  - [2,3]
  - 4

you would need:

loop: "{{ [1, [2,3] ,4] | flatten(1) }}"

• Any with_* statement that requires using lookup within a loop should not be converted to use the loop keyword. For example, instead of doing:

loop: "{{ lookup('fileglob', '*.txt', wantlist=True) }}"

it’s cleaner to keep:

with_fileglob: '*.txt'

Standard loops

Iterating over a simple list

Repeated tasks can be written as standard loops over a simple list of strings. You can define the list directly in the task:

- name: add several users
  user:
    name: "{{ item }}"
    state: present
    groups: "wheel"
  loop:
     - testuser1
     - testuser2

You can define the list in a variables file, or in the ‘vars’ section of your play, then refer to the name of the list in the task:

loop: "{{ somelist }}"

Either of these examples would be the equivalent of:

- name: add user testuser1
  user:
    name: "testuser1"
    state: present
    groups: "wheel"

- name: add user testuser2
  user:
    name: "testuser2"
    state: present
    groups: "wheel"

You can pass a list directly to a parameter for some plugins. Most of the packaging modules, like yum – Manages packages with the yum package manager and apt – Manages apt-packages, have this capability. When available, passing the list to a parameter is better than looping over the task. For example:

- name: optimal yum
  yum:
    name: "{{  list_of_packages  }}"
    state: present

- name: non-optimal yum, slower and may cause issues with interdependencies
  yum:
    name: "{{  item  }}"
    state: present
  loop: "{{  list_of_packages  }}"

Check the module documentation to see if you can pass a list to any particular module’s parameter(s).

Iterating over a list of hashes

If you have a list of hashes, you can reference subkeys in a loop. For example:

- name: add several users
  user:
    name: "{{ item.name }}"
    state: present
    groups: "{{ item.groups }}"
  loop:
    - { name: 'testuser1', groups: 'wheel' }
    - { name: 'testuser2', groups: 'root' }

When combining Conditionals with a loop, the when: statement is processed separately for each item. See The When Statement for examples.

Iterating over a dictionary

To loop over a dict, use the dict2items Dict Filter:

- name: create a tag dictionary of non-empty tags
  set_fact:
    tags_dict: "{{ (tags_dict|default({}))|combine({item.key: item.value}) }}"
  loop: "{{ tags|dict2items }}"
  vars:
    tags:
      Environment: dev
      Application: payment
      Another: "{{ doesnotexist|default() }}"
  when: item.value != ""

Here, we don’t want to set empty tags, so we create a dictionary containing only non-empty tags.

Registering variables with a loop

You can register the output of a loop as a variable. For example:

- shell: "echo {{ item }}"
  loop:
    - "one"
    - "two"
  register: echo

When you use register with a loop, the data structure placed in the variable will contain a results attribute that is a list of all responses from the module. This differs from the data structure returned when using register without a loop:

{
    "changed": true,
    "msg": "All items completed",
    "results": [
        {
            "changed": true,
            "cmd": "echo \"one\" ",
            "delta": "0:00:00.003110",
            "end": "2013-12-19 12:00:05.187153",
            "invocation": {
                "module_args": "echo \"one\"",
                "module_name": "shell"
            },
            "item": "one",
            "rc": 0,
            "start": "2013-12-19 12:00:05.184043",
            "stderr": "",
            "stdout": "one"
        },
        {
            "changed": true,
            "cmd": "echo \"two\" ",
            "delta": "0:00:00.002920",
            "end": "2013-12-19 12:00:05.245502",
            "invocation": {
                "module_args": "echo \"two\"",
                "module_name": "shell"
            },
            "item": "two",
            "rc": 0,
            "start": "2013-12-19 12:00:05.242582",
            "stderr": "",
            "stdout": "two"
        }
    ]
}

Subsequent loops over the registered variable to inspect the results may look like:

- name: Fail if return code is not 0
  fail:
    msg: "The command ({{ item.cmd }}) did not have a 0 return code"
  when: item.rc != 0
  loop: "{{ echo.results }}"

During iteration, the result of the current item will be placed in the variable:

- shell: echo "{{ item }}"
  loop:
    - one
    - two
  register: echo
  changed_when: echo.stdout != "one"

Complex loops

Iterating over nested lists

You can use Jinja2 expressions to iterate over complex lists. For example, a loop can combine nested lists:

- name: give users access to multiple databases
  mysql_user:
    name: "{{ item[0] }}"
    priv: "{{ item[1] }}.*:ALL"
    append_privs: yes
    password: "foo"
  loop: "{{ ['alice', 'bob'] |product(['clientdb', 'employeedb', 'providerdb'])|list }}"

Retrying a task until a condition is met

You can use the until keyword to retry a task until a certain condition is met. Here’s an example:

- shell: /usr/bin/foo
  register: result
  until: result.stdout.find("all systems go") != -1
  retries: 5
  delay: 10

This task runs up to 5 times with a delay of 10 seconds between each attempt. If the result of any attempt has “all systems go” in its stdout, the task succeeds. The default value for “retries” is 3 and “delay” is 5.

To see the results of individual retries, run the play with -vv.

When you run a task with until and register the result as a variable, the registered variable will include a key called “attempts”, which records the number of the retries for the task.

Looping over inventory

To loop over your inventory, or just a subset of it, you can use a regular loop with the ansible_play_batch or groups variables:

# show all the hosts in the inventory
- debug:
    msg: "{{ item }}"
  loop: "{{ groups['all'] }}"

# show all the hosts in the current play
- debug:
    msg: "{{ item }}"
  loop: "{{ ansible_play_batch }}"

There is also a specific lookup plugin inventory_hostnames that can be used like this:

# show all the hosts in the inventory
- debug:
    msg: "{{ item }}"
  loop: "{{ query('inventory_hostnames', 'all') }}"

# show all the hosts matching the pattern, ie all but the group www
- debug:
    msg: "{{ item }}"
  loop: "{{ query('inventory_hostnames', 'all:!www') }}"

More information on the patterns can be found on Patterns: targeting hosts and groups

Ensuring list input for loop: query vs. lookup

The loop keyword requires a list as input, but the lookup keyword returns a string of comma-separated values by default. Ansible 2.5 introduced a new Jinja2 function named Invoking lookup plugins with query that always returns a list, offering a simpler interface and more predictable output from lookup plugins when using the loop keyword.

You can force lookup to return a list to loop by using wantlist=True, or you can use query instead.

These examples do the same thing:

loop: "{{ query('inventory_hostnames', 'all') }}"

loop: "{{ lookup('inventory_hostnames', 'all', wantlist=True) }}"

Adding controls to loops

The loop_control keyword lets you manage your loops in useful ways.

Limiting loop output with label

When looping over complex data structures, the console output of your task can be enormous. To limit the displayed output, use the label directive with loop_control:

- name: create servers
  digital_ocean:
    name: "{{ item.name }}"
    state: present
  loop:
    - name: server1
      disks: 3gb
      ram: 15Gb
      network:
        nic01: 100Gb
        nic02: 10Gb
        ...
  loop_control:
    label: "{{ item.name }}"

The output of this task will display just the name field for each item instead of the entire contents of the multi-line {{ item }} variable.

Pausing within a loop

To control the time (in seconds) between the execution of each item in a task loop, use the pause directive with loop_control:

# main.yml
- name: create servers, pause 3s before creating next
  digital_ocean:
    name: "{{ item }}"
    state: present
  loop:
    - server1
    - server2
  loop_control:
    pause: 3

Tracking progress through a loop with index_var

To keep track of where you are in a loop, use the index_var directive with loop_control. This directive specifies a variable name to contain the current loop index:

- name: count our fruit
  debug:
    msg: "{{ item }} with index {{ my_idx }}"
  loop:
    - apple
    - banana
    - pear
  loop_control:
    index_var: my_idx

Defining inner and outer variable names with loop_var

You can nest two looping tasks using include_tasks. However, by default Ansible sets the loop variable item for each loop. This means the inner, nested loop will overwrite the value of item from the outer loop. You can specify the name of the variable for each loop using loop_var with loop_control:

# main.yml
- include_tasks: inner.yml
  loop:
    - 1
    - 2
    - 3
  loop_control:
    loop_var: outer_item

# inner.yml
- debug:
    msg: "outer item={{ outer_item }} inner item={{ item }}"
  loop:
    - a
    - b
    - c

Extended loop variables

As of Ansible 2.8 you can get extended loop information using the extended option to loop control. This option will expose the following information.

Variable	Description
ansible_loop.allitems	The list of all items in the loop
ansible_loop.index	The current iteration of the loop. (1 indexed)
ansible_loop.index0	The current iteration of the loop. (0 indexed)
ansible_loop.revindex	The number of iterations from the end of the loop (1 indexed)
ansible_loop.revindex0	The number of iterations from the end of the loop (0 indexed)
ansible_loop.first	True if first iteration
ansible_loop.last	True if last iteration
ansible_loop.length	The number of items in the loop
ansible_loop.previtem	The item from the previous iteration of the loop. Undefined during the first iteration.
ansible_loop.nextitem	The item from the following iteration of the loop. Undefined during the last iteration.

loop_control:
  extended: yes

Accessing the name of your loop_var

As of Ansible 2.8 you can get the name of the value provided to loop_control.loop_var using the ansible_loop_var variable

For role authors, writing roles that allow loops, instead of dictating the required loop_var value, you can gather the value via:

"{{ lookup('vars', ansible_loop_var) }}"

Migrating from with_X to loop

With the release of Ansible 2.5, the recommended way to perform loops is the use the new loop keyword instead of with_X style loops.

In many cases, loop syntax is better expressed using filters instead of more complex use of query or lookup.

The following examples will show how to convert many common with_ style loops to loop and filters.

with_list

with_list is directly replaced by loop.

- name: with_list
  debug:
    msg: "{{ item }}"
  with_list:
    - one
    - two

- name: with_list -> loop
  debug:
    msg: "{{ item }}"
  loop:
    - one
    - two

with_items

with_items is replaced by loop and the flatten filter.

- name: with_items
  debug:
    msg: "{{ item }}"
  with_items: "{{ items }}"

- name: with_items -> loop
  debug:
    msg: "{{ item }}"
  loop: "{{ items|flatten(levels=1) }}"

with_indexed_items

with_indexed_items is replaced by loop, the flatten filter and loop_control.index_var.

- name: with_indexed_items
  debug:
    msg: "{{ item.0 }} - {{ item.1 }}"
  with_indexed_items: "{{ items }}"

- name: with_indexed_items -> loop
  debug:
    msg: "{{ index }} - {{ item }}"
  loop: "{{ items|flatten(levels=1) }}"
  loop_control:
    index_var: index

with_flattened

with_flattened is replaced by loop and the flatten filter.

- name: with_flattened
  debug:
    msg: "{{ item }}"
  with_flattened: "{{ items }}"

- name: with_flattened -> loop
  debug:
    msg: "{{ item }}"
  loop: "{{ items|flatten }}"

with_together

with_together is replaced by loop and the zip filter.

- name: with_together
  debug:
    msg: "{{ item.0 }} - {{ item.1 }}"
  with_together:
    - "{{ list_one }}"
    - "{{ list_two }}"

- name: with_together -> loop
  debug:
    msg: "{{ item.0 }} - {{ item.1 }}"
  loop: "{{ list_one|zip(list_two)|list }}"

with_dict

with_dict can be substituted by loop and either the dictsort or dict2items filters.

- name: with_dict
  debug:
    msg: "{{ item.key }} - {{ item.value }}"
  with_dict: "{{ dictionary }}"

- name: with_dict -> loop (option 1)
  debug:
    msg: "{{ item.key }} - {{ item.value }}"
  loop: "{{ dictionary|dict2items }}"

- name: with_dict -> loop (option 2)
  debug:
    msg: "{{ item.0 }} - {{ item.1 }}"
  loop: "{{ dictionary|dictsort }}"

with_sequence

with_sequence is replaced by loop and the range function, and potentially the format filter.

- name: with_sequence
  debug:
    msg: "{{ item }}"
  with_sequence: start=0 end=4 stride=2 format=testuser%02x

- name: with_sequence -> loop
  debug:
    msg: "{{ 'testuser%02x' | format(item) }}"
  # range is exclusive of the end point
  loop: "{{ range(0, 4 + 1, 2)|list }}"

with_subelements

with_subelements is replaced by loop and the subelements filter.

- name: with_subelements
  debug:
    msg: "{{ item.0.name }} - {{ item.1 }}"
  with_subelements:
    - "{{ users }}"
    - mysql.hosts

- name: with_subelements -> loop
  debug:
    msg: "{{ item.0.name }} - {{ item.1 }}"
  loop: "{{ users|subelements('mysql.hosts') }}"

with_nested/with_cartesian

with_nested and with_cartesian are replaced by loop and the product filter.

- name: with_nested
  debug:
    msg: "{{ item.0 }} - {{ item.1 }}"
  with_nested:
    - "{{ list_one }}"
    - "{{ list_two }}"

- name: with_nested -> loop
  debug:
    msg: "{{ item.0 }} - {{ item.1 }}"
  loop: "{{ list_one|product(list_two)|list }}"

with_random_choice

with_random_choice is replaced by just use of the random filter, without need of loop.

- name: with_random_choice
  debug:
    msg: "{{ item }}"
  with_random_choice: "{{ my_list }}"

- name: with_random_choice -> loop (No loop is needed here)
  debug:
    msg: "{{ my_list|random }}"
  tags: random