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_*
- 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
- 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
ansible.builtin.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
ansible.builtin.user:
name: "testuser1"
state: present
groups: "wheel"
- name: Add user testuser2
ansible.builtin.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 and apt, have this capability. When available, passing the list to a parameter is better than looping over the task. For example:
- name: Optimal yum
ansible.builtin.yum:
name: "{{ list_of_packages }}"
state: present
- name: Non-optimal yum, slower and may cause issues with interdependencies
ansible.builtin.yum:
name: "{{ item }}"
state: present
loop: "{{ list_of_packages }}"
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
ansible.builtin.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 Basic conditionals with when for examples.
Iterating over a dictionary
To loop over a dict, use the dict2items:
- name: Using dict2items
ansible.builtin.debug:
msg: "{{ item.key }} - {{ item.value }}"
loop: "{{ tag_data | dict2items }}"
vars:
tag_data:
Environment: dev
Application: payment
Here, we are iterating over tag_data and printing the key and the value from it.
Registering variables with a loop
You can register the output of a loop as a variable. For example:
- name: Register loop output as a variable
ansible.builtin.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
ansible.builtin.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:
- name: Place the result of the current item in the variable
ansible.builtin.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
community.mysql.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:
- name: Retry a task until a certain condition is met
ansible.builtin.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.
Note
You must set the until parameter if you want a task to retry. If until is not defined, the value for the retries parameter is forced to 1.
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:
- name: Show all the hosts in the inventory
ansible.builtin.debug:
msg: "{{ item }}"
loop: "{{ groups['all'] }}"
- name: Show all the hosts in the current play
ansible.builtin.debug:
msg: "{{ item }}"
loop: "{{ ansible_play_batch }}"
There is also a specific lookup plugin inventory_hostnames that can be used like this:
- name: Show all the hosts in the inventory
ansible.builtin.debug:
msg: "{{ item }}"
loop: "{{ query('inventory_hostnames', 'all') }}"
- name: Show all the hosts matching the pattern, ie all but the group www
ansible.builtin.debug:
msg: "{{ item }}"
loop: "{{ query('inventory_hostnames', 'all:!www') }}"
Ensuring list input for loop: using query rather than 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 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.
Note
This is for making console output more readable, not protecting sensitive data. If there is sensitive data in loop, set no_log: yes on the task to prevent disclosure.
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
community.digitalocean.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
ansible.builtin.debug:
msg: "{{ item }} with index {{ my_idx }}"
loop:
- apple
- banana
- pear
loop_control:
index_var: my_idx
Note
index_var is 0 indexed.
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
- name: Print outer and inner items
ansible.builtin.debug:
msg: "outer item={{ outer_item }} inner item={{ item }}"
loop:
- a
- b
- c
Note
If Ansible detects that the current loop is using a variable which has already been defined, it will raise an error to fail the task.
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 |
| The list of all items in the loop |
| The current iteration of the loop. (1 indexed) |
| The current iteration of the loop. (0 indexed) |
| The number of iterations from the end of the loop (1 indexed) |
| The number of iterations from the end of the loop (0 indexed) |
|
|
|
|
| The number of items in the loop |
| The item from the previous iteration of the loop. Undefined during the first iteration. |
| 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
Migrating from with_X to loop
In most cases, loops work best with the loop keyword instead of with_X style loops. The loop syntax is usually best expressed using filters instead of more complex use of query or lookup.
These examples 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
ansible.builtin.debug:
msg: "{{ item }}"
with_list:
- one
- two
- name: with_list -> loop
ansible.builtin.debug:
msg: "{{ item }}"
loop:
- one
- two
with_items
with_items is replaced by loop and the flatten filter.
- name: with_items
ansible.builtin.debug:
msg: "{{ item }}"
with_items: "{{ items }}"
- name: with_items -> loop
ansible.builtin.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
ansible.builtin.debug:
msg: "{{ item.0 }} - {{ item.1 }}"
with_indexed_items: "{{ items }}"
- name: with_indexed_items -> loop
ansible.builtin.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
ansible.builtin.debug:
msg: "{{ item }}"
with_flattened: "{{ items }}"
- name: with_flattened -> loop
ansible.builtin.debug:
msg: "{{ item }}"
loop: "{{ items|flatten }}"
with_together
with_together is replaced by loop and the zip filter.
- name: with_together
ansible.builtin.debug:
msg: "{{ item.0 }} - {{ item.1 }}"
with_together:
- "{{ list_one }}"
- "{{ list_two }}"
- name: with_together -> loop
ansible.builtin.debug:
msg: "{{ item.0 }} - {{ item.1 }}"
loop: "{{ list_one|zip(list_two)|list }}"
Another example with complex data
- name: with_together -> loop
ansible.builtin.debug:
msg: "{{ item.0 }} - {{ item.1 }} - {{ item.2 }}"
loop: "{{ data[0]|zip(*data[1:])|list }}"
vars:
data:
- ['a', 'b', 'c']
- ['d', 'e', 'f']
- ['g', 'h', 'i']
with_dict
with_dict can be substituted by loop and either the dictsort or dict2items filters.
- name: with_dict
ansible.builtin.debug:
msg: "{{ item.key }} - {{ item.value }}"
with_dict: "{{ dictionary }}"
- name: with_dict -> loop (option 1)
ansible.builtin.debug:
msg: "{{ item.key }} - {{ item.value }}"
loop: "{{ dictionary|dict2items }}"
- name: with_dict -> loop (option 2)
ansible.builtin.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
ansible.builtin.debug:
msg: "{{ item }}"
with_sequence: start=0 end=4 stride=2 format=testuser%02x
- name: with_sequence -> loop
ansible.builtin.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
ansible.builtin.debug:
msg: "{{ item.0.name }} - {{ item.1 }}"
with_subelements:
- "{{ users }}"
- mysql.hosts
- name: with_subelements -> loop
ansible.builtin.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
ansible.builtin.debug:
msg: "{{ item.0 }} - {{ item.1 }}"
with_nested:
- "{{ list_one }}"
- "{{ list_two }}"
- name: with_nested -> loop
ansible.builtin.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
ansible.builtin.debug:
msg: "{{ item }}"
with_random_choice: "{{ my_list }}"
- name: with_random_choice -> loop (No loop is needed here)
ansible.builtin.debug:
msg: "{{ my_list|random }}"
tags: random
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