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>
.
Note
We added
loop
in Ansible 2.5. It is not yet a full replacement forwith_<lookup>
, but we recommend it for most use cases.We have not deprecated the use of
with_<lookup>
- that syntax will still be valid for the foreseeable future.We are looking to improve
loop
syntax - watch this page and the changelog for updates.
Comparing loop
and with_*
¶
The
with_<lookup>
keywords rely on Lookup Plugins - evenitems
is a lookup.The
loop
keyword is equivalent towith_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 useloop
.Be careful when changing
with_items
toloop
, aswith_items
performed implicit single-level flattening. You may need to useflatten(1)
withloop
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 usinglookup
within a loop should not be converted to use theloop
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_module and apt_module, 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¶
New in version 1.4.
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.
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:
# 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¶
New in version 2.1.
The loop_control
keyword lets you manage your loops in useful ways.
Limiting loop output with label
¶
New in version 2.2.
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¶
New in version 2.2.
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
¶
New in version 2.5.
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
¶
New in version 2.1.
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
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¶
New in version 2.8.
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¶
New in version 2.8.
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
See also
- About Playbooks
An introduction to playbooks
- Roles
Playbook organization by roles
- Best Practices
Best practices in playbooks
- Conditionals
Conditional statements in playbooks
- Using Variables
All about variables
- User Mailing List
Have a question? Stop by the google group!
- irc.freenode.net
#ansible IRC chat channel