Often you’ll want to do many things in one task, such as create a lot of users, install a lot of packages, or repeat a polling step until a certain result is reached.
This chapter is all about how to use loops in playbooks.
Topics
To save some typing, repeated tasks can be written in short-hand like so:
- name: add several users
user:
name: "{{ item }}"
state: present
groups: "wheel"
loop:
- testuser1
- testuser2
If you have defined a YAML list in a variables file, or the ‘vars’ section, you can also do:
loop: "{{ somelist }}"
The above 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"
Note
Before 2.5 Ansible mainly used the with_<lookup> keywords to create loops, the loop keyword is basically analogous to with_list.
Some plugins like, the yum and apt modules can take lists directly to their options, this is more optimal than looping over the task. See each action’s documentation for details, for now here is an example:
- name: optimal yum
yum:
name: "{{list_of_packages}}"
state: present
- name: non optimal yum, not only slower but might cause issues with interdependencies
yum:
name: "{{item}}"
state: present
loop: "{{list_of_packages}}"
Note that the types of items you iterate over do not have to be simple lists of strings. If you have a list of hashes, you can reference subkeys using things like:
- name: add several users
user:
name: "{{ item.name }}"
state: present
groups: "{{ item.groups }}"
loop:
- { name: 'testuser1', groups: 'wheel' }
- { name: 'testuser2', groups: 'root' }
Also be aware that when combining Conditionals with a loop, the when: statement is processed separately for each item.
See The When Statement for an example.
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.
Sometimes you need more than what a simple list provides, you can use Jinja2 expressions to create complex lists: For example, using the ‘nested’ lookup, you can combine 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 }}"
Note
with_ loops are actually a combination of things with_ + lookup(), even items is a lookup. loop can be used in the same way as shown above.
In Ansible 2.5 a new jinja2 function was introduced named query, that offers several benefits over lookup when using the new loop keyword.
This is described more in the lookup documentation, however, query provides a more simple interface and a more predictable output from lookup plugins, ensuring better compatibility with loop.
In certain situations the lookup function may not return a list which loop requires.
The following invocations are equivalent, using wantlist=True with lookup to ensure a return type of a list:
loop: "{{ query('inventory_hostnames', 'all') }}"
loop: "{{ lookup('inventory_hostnames', 'all', wantlist=True) }}"
New in version 1.4.
Sometimes you would want 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
The above example run the shell module recursively till the module’s result has “all systems go” in its stdout or the task has been retried for 5 times with a delay of 10 seconds. The default value for “retries” is 3 and “delay” is 5.
The task returns the results returned by the last task run. The results of individual retries can be viewed by -vv option. The registered variable will also have a new key “attempts” which will have the number of the retries for the task.
Note
If the until parameter isn’t defined, the value for the retries parameter is forced to 1.
After using 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.
Here is an example of using register with loop:
- shell: "echo {{ item }}"
loop:
- "one"
- "two"
register: echo
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"
If you wish to loop over the inventory, or just a subset of it, there are multiple ways.
One can use a regular loop with the ansible_play_batch or groups variables, like this:
# 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 Working with Patterns
New in version 2.1.
In 2.0 you are again able to use loops and task includes (but not playbook includes). This adds the ability to loop over the set of tasks in one shot.
Ansible by default sets the loop variable item for each loop, which causes these nested loops to overwrite the value of item from the “outer” loops.
As of Ansible 2.1, the loop_control option can be used to specify the name of the variable to be used for the loop:
# 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.
New in version 2.2.
When using complex data structures for looping the display might get a bit too “busy”, this is where the label directive comes to help:
- 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 }}"
This will now display just the label field instead of the whole structure per item, it defaults to {{ item }} to display things as usual.
New in version 2.2.
Another option to loop control is pause, which allows you to control the time (in seconds) between execution of items in a task loop.:
# main.yml
- name: create servers, pause 3s before creating next
digital_ocean:
name: "{{ item }}"
state: present
loop:
- server1
- server2
loop_control:
pause: 3
New in version 2.5.
If you need to keep track of where you are in a loop, you can use the index_var option to loop control to specify 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
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 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 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 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 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 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 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 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 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 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 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