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"
with_items:
- testuser1
- testuser2
If you have defined a YAML list in a variables file, or the ‘vars’ section, you can also do:
with_items: "{{ 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"
The yum and apt modules use with_items to execute fewer package manager transactions.
Note that the types of items you iterate over with ‘with_items’ 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 }}"
with_items:
- { name: 'testuser1', groups: 'wheel' }
- { name: 'testuser2', groups: 'root' }
Also be aware that when combining when with with_items (or any other loop statement), the when statement is processed separately for each item. See The When Statement for an example.
Loops are actually a combination of things with_ + lookup(), so any lookup plugin can be used as a source for a loop, ‘items’ is lookup.
Loops can be nested as well:
- name: give users access to multiple databases
mysql_user:
name: "{{ item[0] }}"
priv: "{{ item[1] }}.*:ALL"
append_privs: yes
password: "foo"
with_nested:
- [ 'alice', 'bob' ]
- [ 'clientdb', 'employeedb', 'providerdb' ]
As with the case of ‘with_items’ above, you can use previously defined variables.:
- name: here, 'users' contains the above list of employees
mysql_user:
name: "{{ item[0] }}"
priv: "{{ item[1] }}.*:ALL"
append_privs: yes
password: "foo"
with_nested:
- "{{ users }}"
- [ 'clientdb', 'employeedb', 'providerdb' ]
1.5 新版功能.
Suppose you have the following variable:
---
users:
alice:
name: Alice Appleworth
telephone: 123-456-7890
bob:
name: Bob Bananarama
telephone: 987-654-3210
And you want to print every user’s name and phone number. You can loop through the elements of a hash using with_dict like this:
tasks:
- name: Print phone records
debug:
msg: "User {{ item.key }} is {{ item.value.name }} ({{ item.value.telephone }})"
with_dict: "{{ users }}"
with_file iterates over the content of a list of files, item will be set to the content of each file in sequence. It can be used like this:
---
- hosts: all
tasks:
# emit a debug message containing the content of each file.
- debug:
msg: "{{ item }}"
with_file:
- first_example_file
- second_example_file
Assuming that first_example_file contained the text “hello” and second_example_file contained the text “world”, this would result in:
TASK [debug msg={{ item }}] ******************************************************
ok: [localhost] => (item=hello) => {
"item": "hello",
"msg": "hello"
}
ok: [localhost] => (item=world) => {
"item": "world",
"msg": "world"
}
with_fileglob matches all files in a single directory, non-recursively, that match a pattern. It calls
Python’s glob library, and can be used like this:
---
- hosts: all
tasks:
# first ensure our target directory exists
- name: Ensure target directory exists
file:
dest: "/etc/fooapp"
state: directory
# copy each file over that matches the given pattern
- name: Copy each file over that matches the given pattern
copy:
src: "{{ item }}"
dest: "/etc/fooapp/"
owner: "root"
mode: 0600
with_fileglob:
- "/playbooks/files/fooapp/*"
注解
When using a relative path with with_fileglob in a role, Ansible resolves the path relative to the roles/<rolename>/files directory.
注解
This is an uncommon thing to want to do, but we’re documenting it for completeness. You probably won’t be reaching for this one often.
Suppose you have the following variable data was loaded in via somewhere:
---
alpha: [ 'a', 'b', 'c', 'd' ]
numbers: [ 1, 2, 3, 4 ]
And you want the set of ‘(a, 1)’ and ‘(b, 2)’ and so on. Use ‘with_together’ to get this:
tasks:
- debug:
msg: "{{ item.0 }} and {{ item.1 }}"
with_together:
- "{{ alpha }}"
- "{{ numbers }}"
Suppose you want to do something like loop over a list of users, creating them, and allowing them to login by a certain set of SSH keys.
How might that be accomplished? Let’s assume you had the following defined and loaded in via “vars_files” or maybe a “group_vars/all” file:
---
users:
- name: alice
authorized:
- /tmp/alice/onekey.pub
- /tmp/alice/twokey.pub
mysql:
password: mysql-password
hosts:
- "%"
- "127.0.0.1"
- "::1"
- "localhost"
privs:
- "*.*:SELECT"
- "DB1.*:ALL"
- name: bob
authorized:
- /tmp/bob/id_rsa.pub
mysql:
password: other-mysql-password
hosts:
- "db1"
privs:
- "*.*:SELECT"
- "DB2.*:ALL"
It might happen like so:
- name: Create User
user:
name: "{{ item.name }}"
state: present
generate_ssh_key: yes
with_items:
- "{{ users }}"
- name: Set authorized ssh key
authorized_key:
user: "{{ item.0.name }}"
key: "{{ lookup('file', item.1) }}"
with_subelements:
- "{{ users }}"
- authorized
Given the mysql hosts and privs subkey lists, you can also iterate over a list in a nested subkey:
- name: Setup MySQL users
mysql_user:
name: "{{ item.0.name }}"
password: "{{ item.0.mysql.password }}"
host: "{{ item.1 }}"
priv: "{{ item.0.mysql.privs | join('/') }}"
with_subelements:
- "{{ users }}"
- "{{ mysql.hosts }}"
Subelements walks a list of hashes (aka dictionaries) and then traverses a list with a given (nested sub-)key inside of those records.
Optionally, you can add a third element to the subelements list, that holds a dictionary of flags. Currently you can add the ‘skip_missing’ flag. If set to True, the lookup plugin will skip the lists items that do not contain the given subkey. Without this flag, or if that flag is set to False, the plugin will yield an error and complain about the missing subkey.
The authorized_key pattern is exactly where it comes up most.
with_sequence generates a sequence of items. You
can specify a start value, an end value, an optional “stride” value that specifies the number of steps to increment the sequence, and an optional printf-style format string.
Arguments should be specified as key=value pair strings.
A simple shortcut form of the arguments string is also accepted: [start-]end[/stride][:format].
Numerical values can be specified in decimal, hexadecimal (0x3f8) or octal (0600). Negative numbers are not supported. This works as follows:
---
- hosts: all
tasks:
# create groups
- group:
name: "evens"
state: present
- group:
name: "odds"
state: present
# create some test users
- user:
name: "{{ item }}"
state: present
groups: "evens"
with_sequence: start=0 end=32 format=testuser%02x
# create a series of directories with even numbers for some reason
- file:
dest: "/var/stuff/{{ item }}"
state: directory
with_sequence: start=4 end=16 stride=2
# a simpler way to use the sequence plugin
# create 4 groups
- group:
name: "group{{ item }}"
state: present
with_sequence: count=4
The ‘random_choice’ feature can be used to pick something at random. While it’s not a load balancer (there are modules for those), it can somewhat be used as a poor man’s load balancer in a MacGyver like situation:
- debug:
msg: "{{ item }}"
with_random_choice:
- "go through the door"
- "drink from the goblet"
- "press the red button"
- "do nothing"
One of the provided strings will be selected at random.
At a more basic level, they can be used to add chaos and excitement to otherwise predictable automation environments.
1.4 新版功能.
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.
注解
This is an uncommon thing to want to do, but we’re documenting it for completeness. You probably won’t be reaching for this one often.
This isn’t exactly a loop, but it’s close. What if you want to use a reference to a file based on the first file found that matches a given criteria, and some of the filenames are determined by variable names? Yes, you can do that as follows:
- name: INTERFACES | Create Ansible header for /etc/network/interfaces
template:
src: "{{ item }}"
dest: "/etc/foo.conf"
with_first_found:
- "{{ ansible_virtualization_type }}_foo.conf"
- "default_foo.conf"
This tool also has a long form version that allows for configurable search paths. Here’s an example:
- name: some configuration template
template:
src: "{{ item }}"
dest: "/etc/file.cfg"
mode: 0444
owner: "root"
group: "root"
with_first_found:
- files:
- "{{ inventory_hostname }}/etc/file.cfg"
paths:
- ../../../templates.overwrites
- ../../../templates
- files:
- etc/file.cfg
paths:
- templates
注解
This is an uncommon thing to want to do, but we’re documenting it for completeness. You probably won’t be reaching for this one often.
Sometimes you might want to execute a program, and based on the output of that program, loop over the results of that line by line. Ansible provides a neat way to do that, though you should remember, this is always executed on the control machine, not the remote machine:
- name: Example of looping over a command result
shell: "/usr/bin/frobnicate {{ item }}"
with_lines:
- "/usr/bin/frobnications_per_host --param {{ inventory_hostname }}"
Ok, that was a bit arbitrary. In fact, if you’re doing something that is inventory related you might just want to write a dynamic inventory source instead (see Dynamic Inventory), but this can be occasionally useful in quick-and-dirty implementations.
Should you ever need to execute a command remotely, you would not use the above method. Instead do this:
- name: Example of looping over a REMOTE command result
shell: "/usr/bin/something"
register: command_result
- name: Do something with each result
shell: "/usr/bin/something_else --param {{ item }}"
with_items:
- "{{ command_result.stdout_lines }}"
注解
This is an uncommon thing to want to do, but we’re documenting it for completeness. You probably won’t be reaching for this one often.
1.3 新版功能.
If you want to loop over an array and also get the numeric index of where you are in the array as you go, you can also do that. It’s uncommonly used:
- name: indexed loop demo
debug:
msg: "at array position {{ item.0 }} there is a value {{ item.1 }}"
with_indexed_items:
- "{{ some_list }}"
2.0 新版功能.
The ini plugin can use regexp to retrieve a set of keys. As a consequence, we can loop over this set. Here is the ini file we’ll use:
[section1]
value1=section1/value1
value2=section1/value2
[section2]
value1=section2/value1
value2=section2/value2
Here is an example of using with_ini:
- debug:
msg: "{{ item }}"
with_ini:
- value[1-2]
- section: section1
- file: "lookup.ini"
- re: true
And here is the returned value:
{
"changed": false,
"msg": "All items completed",
"results": [
{
"invocation": {
"module_args": "msg=\"section1/value1\"",
"module_name": "debug"
},
"item": "section1/value1",
"msg": "section1/value1",
"verbose_always": true
},
{
"invocation": {
"module_args": "msg=\"section1/value2\"",
"module_name": "debug"
},
"item": "section1/value2",
"msg": "section1/value2",
"verbose_always": true
}
]
}
注解
This is an uncommon thing to want to do, but we’re documenting it for completeness. You probably won’t be reaching for this one often.
In rare instances you might have several lists of lists, and you just want to iterate over every item in all of those lists. Assume a really crazy hypothetical datastructure:
----
# file: roles/foo/vars/main.yml
packages_base:
- [ 'foo-package', 'bar-package' ]
packages_apps:
- [ ['one-package', 'two-package' ]]
- [ ['red-package'], ['blue-package']]
As you can see the formatting of packages in these lists is all over the place. How can we install all of the packages in both lists?:
- name: flattened loop demo
yum:
name: "{{ item }}"
state: present
with_flattened:
- "{{ packages_base }}"
- "{{ packages_apps }}"
That’s how!
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 with_items:
- shell: "echo {{ item }}"
with_items:
- "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
with_items: "{{ echo.results }}"
During iteration, the result of the current item will be placed in the variable:
- shell: echo "{{ item }}"
with_items:
- one
- two
register: echo
changed_when: echo.stdout != "one"
If you wish to loop over the inventory, or just a subset of it, there is multiple ways.
One can use a regular with_items with the play_hosts or groups variables, like this:
# show all the hosts in the inventory
- debug:
msg: "{{ item }}"
with_items:
- "{{ groups['all'] }}"
# show all the hosts in the current play
- debug:
msg: "{{ item }}"
with_items:
- "{{ play_hosts }}"
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 }}"
with_inventory_hostnames:
- all
# show all the hosts matching the pattern, ie all but the group www
- debug:
msg: "{{ item }}"
with_inventory_hostnames:
- all:!www
More information on the patterns can be found on Patterns
2.1 新版功能.
In 2.0 you are again able to use with_ 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: inner.yml
with_items:
- 1
- 2
- 3
loop_control:
loop_var: outer_item
# inner.yml
- debug:
msg: "outer item={{ outer_item }} inner item={{ item }}"
with_items:
- a
- b
- c
注解
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.
2.2 新版功能.
When using complex data structures for looping the display might get a bit too “busy”, this is where the C(label) directive comes to help:
- name: create servers
digital_ocean:
name: "{{ item.name }}"
state: present
with_items:
- 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.
2.2 新版功能.
Another option to loop control is C(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
with_items:
- server1
- server2
loop_control:
pause: 3
Because loop_control is not available in Ansible 2.0, when using an include with a loop you should use set_fact to save the “outer” loops value for item:
# main.yml
- include: inner.yml
with_items:
- 1
- 2
- 3
# inner.yml
- set_fact:
outer_item: "{{ item }}"
- debug:
msg: "outer item={{ outer_item }} inner item={{ item }}"
with_items:
- a
- b
- c
While you ordinarily shouldn’t have to, should you wish to write your own ways to loop over arbitrary data structures, you can read Developing Plugins for some starter information. Each of the above features are implemented as plugins in ansible, so there are many implementations to reference.
参见