Clever Geek Handbook

Unraveling Ansible Loops

This post covers the following Ansible loop modules: with_items, with_nested, with_subelements, with_dict.



All of these with * are already deprecated and it is recommended to use loop.



Source



One of my roles at Chromatic is as a member of the DevOps team. Among other things, this includes working with our servers and our clients' servers. This, in turn, means I spend a lot of time working with Ansible , a popular tool for provisioning, configuring, and deploying servers and applications.



Simply put, the machine running Ansible runs commands on another machine via SSH. These commands are specified declaratively (optional) using small sections of YAML called tasks. These TASKS call Ansible modules that specialize in executing options on certain components such as files, databases, etc.



For example, the following task uses the File module ( documentation , code ) to create a specific directory if it doesn't already exist, and modifies its attributes if they aren't already set correctly:



- file:
    path: /home/jenkins/.ssh
    state: directory
    owner: jenkins
    group: jenkins
    mode: 700


Multiple tasks related to one task are grouped into roles, and multiple roles can be grouped into playbooks. You can then use the playbook to perform exactly the same configuration steps on any number of servers at the same time.



Is Ansible declarative?



TASKS Ansible , , TASKS. , , , . , Ansible Copy, . Ansible , :



- name: Copy SSH config file into Alice’s .ssh directory.
  copy:
    src: files/config
    dest: /home/alice/.ssh/config
    owner: alice
    group: alice
    mode: 0600


, , bash, scp, chown chmod. Ansible , .



, , — , , .



, Ansible, — TASKS . , Ansible , , — PHP, .



, Ansible. Loops , «loops _ + lookup(), ». (Lookups) — Ansible, « Ansible », Loops Ansible Github, .



Ansible « », , . Ansible, , , .



Ansible



TASKS, , , , , ( : , , , , !)



:



  1. , : alice, bob, carol dan.



  2. , : .ssh/ loops.



  3. , . , alice :





/home/alice/
├── .ssh/
├── bob/
├── carol/
├── dan/
└── loops/


1. WITH_ITEMS



Ansible , chuck , :



- name: Remove user ‘Chuck’ from the system.
  user:
    name: chuck
    state: absent
    remove: yes


— , Chuck Craig — with_items. with_items ( ), ( ):



- name: Remove users ‘Chuck’ and ‘Craig’ from the system.
  user:
    name: "{{ item }}"
    state: absent
    remove: yes
  with_items:
    - chuck
    - craig


, with_items , alice bob:





users_with_items:
  - name: "alice"
    personal_directories:
      - "bob"
      - "carol"
      - "dan"
  - name: "bob"
    personal_directories:
      - "alice"
      - "carol"
      - "dan"


TASKS


- name: "Loop 1: create users using 'with_items'."
  user:
    name: "{{ item.name }}"
  with_items: "{{ users_with_items }}"


Ansible User users_with_items. , , , , personal_directories ( , personal_directories — ).



Ansible ( Ansible ): TASKS , . , , personal_directories TASKS (. . User, File).



with_items , PHP:



<?php

foreach ($users_with_items as $user) {
  // Do something with $user...
}


, , :



• item.name .



• with_items, .



, Ansible item, item.property.





/home/
├── alice/
└── bob/


2: , WITH_NESTED



: 2 , 1. chown failed: failed to look up user



, users_with_items 1, , common_directories, , . , ( PHP), -, :



<?php

foreach ($users_with_items as $user) {
  foreach ($common_directories as $directory) {
    // Create $directory for $user...
  }
}


Ansible with_nested. with_nested , :





users_with_items:
  - name: "alice"
    personal_directories:
      - "bob"
      - "carol"
      - "dan"
  - name: "bob"
    personal_directories:
      - "alice"
      - "carol"
      - "dan"

common_directories:
  - ".ssh"
  - "loops


TASKS


# Note that this does not set correct permissions on /home/{{ item.x.name }}/.ssh!
- name: "Loop 2: create common users' directories using 'with_nested'."
  file:
    dest: "/home/{{ item.0.name }}/{{ item.1 }}"
    owner: "{{ item.0.name }}"
    group: "{{ item.0.name }}"
    state: directory
  with_nested:
    - "{{ users_with_items }}"
    - "{{ common_directories }}"


, with_nested , item.0 ( users_with_items) item.1 ( common_directories) . , , /home/alice/.ssh .





/home/
├── alice/
│   ├── .ssh/
│   └── loops/
└── bob/
    ├── .ssh/
    └── loops/


3: , WITH_SUBELEMENTS



: 3 , 1. chown failed: failed to look up user



with_subelements , users_with_items 1. PHP :



<?php

foreach ($users_with_items as $user) {
  foreach ($user['personal_directories'] as $directory) {
    // Create $directory for $user...
  }
}


, $users_with_items $user['personal_directories'] .





users_with_items:
  - name: "alice"
    personal_directories:
      - "bob"
      - "carol"
      - "dan"
  - name: "bob"
    personal_directories:
      - "alice"
      - "carol"
      - "dan"


TASKS


- name: "Loop 3: create personal users' directories using 'with_subelements'."
  file:
    dest: "/home/{{ item.0.name }}/{{ item.1 }}"
    owner: "{{ item.0.name }}"
    group: "{{ item.0.name }}"
    state: directory
  with_subelements:
    - "{{ users_with_items }}"
    - personal_directories


with_subelements , with_nested, , , — personal_directories. 2, ( ) /home/alice/bob.





/home/
├── alice/
│   ├── .ssh/
│   ├── bob/
│   ├── carol/
│   ├── dan/
│   └── loops/
└── bob/
    ├── .ssh/
    ├── alice/
    ├── carol/
    ├── dan/
    └── loops/


4: WITH_DICT



3 , alice bob, , , carol dan. users_with_dict Ansible with_dict.



, (dict dictionary — Python ); with_dict , . , Ansible, PHP :



<?php

foreach ($users_with_dict as $user => $properties) {
  // Create a user named $user...
}




users_with_dict:
  carol:
    common_directories: "{{ common_directories }}"
  dan:
    common_directories: "{{ common_directories }}"


TASKS


- name: "Loop 4: create users using 'with_dict'."
  user:
    name: "{{ item.key }}"
  with_dict: "{{ users_with_dict }}"


with_dict . , , , dict with_dict (, , with_dict ).





/home/
├── alice/
│   ├── .ssh/
│   ├── bob/
│   ├── carol/
│   ├── dan/
│   └── loops/
├── bob/
│   ├── .ssh/
│   ├── alice/
│   ├── carol/
│   ├── dan/
│   └── loops/
├── carol/
└── dan/


5: ,



users_with_dict, Ansible, -. alice, bob, carol dan, with_nested /home/. , , , TASKS:



  • Ansible

    • Ansible
    • Jinja2 ()
    • Jinja2 ()




common_directories:
  - ".ssh"
  - "loops"


TASKS


- name: "Get list of extant users."
  shell: "find * -type d -prune | sort"
  args:
    chdir: "/home"
  register: "home_directories"
  changed_when: false

- name: "Loop 5: create personal user directories if they don't exist."
  file:
    dest: "/home/{{ item.0 }}/{{ item.1 }}"
    owner: "{{ item.0 }}"
    group: "{{ item.0 }}"
    state: directory
  with_nested:
    - "{{ home_directories.stdout_lines }}"
    - "{{ home_directories.stdout_lines | union(common_directories) }}"
  when: "'{{ item.0 }}' != '{{ item.1 }}'"


TASKS: shell find , file .



/home find \ -type d -prune | sort ( shell) , /home, , , .



home_directories register: "home_directories" . , , :



"stdout_lines": [
  "alice",
  "bob",
  "carol",
  "dan",
],


( ) with_nested , :



  1. with_nested :


- "{{ home_directories.stdout_lines | union(common_directories) }}"


  1. , when TASKS:



    when: "'{{ item.0 }}' != '{{ item.1 }}'"




. with_nested Jinja2 TASKS ( home_directories.stdout_lines). Jinja:



  • (home_directories.stdout_lines)
  • (|)
  • , (union (common_directories))


, home_directories.stdout_lines common_directories :



item:
  - .ssh
  - alice
  - bob
  - carol
  - dan
  - loops


, with_nested home_directories.stdout_lines ( with_nested) , .



, — , , , ! (, /home/alice/alice, /home/bob/bob . .) Ansible — when — :



when: "'{{ item.0 }}' != '{{ item.1 }}'"


, home_directories.stdout_lines home_directories.stdout_lines ( Ansible Loops, «… when with_items ( ), when »). PHP , , :



<?php

$users = ['alice', 'bob', 'carol', 'dan'];
$common_directories = ['.ssh', 'loops'];
$directories = $user + $common_directories;

foreach ($users as $user) {
  foreach ($directories as $directory) {
    if ($directory != $user) {
      // Create the directory…
    }
  }
}


, , .





/home/
├── alice/
│   ├── .ssh/
│   ├── bob/
│   ├── carol/
│   ├── dan/
│   └── loops/
├── bob/
│   ├── .ssh/
│   ├── alice/
│   ├── carol/
│   ├── dan/
│   └── loops/
├── carol/
│   ├── .ssh/
│   ├── alice/
│   ├── bob/
│   ├── dan/
│   └── loops/
└── dan/
    ├── .ssh/
    ├── alice/
    ├── bob/
    ├── carol/
    └── loops/




Ansible . ( Ansible), , (with_nested? with_subitems?) .



, , TASKS, ( , array_filter, array_reduce, array_map , ). , , — — .



Hopefully this post will help you out of my initial difficulty. To this end, I built a Vagrant virtual machine (Vagrant natively supports using Ansible for provisioning) and an Ansible playbook that I used to create and test these examples). Just follow the instructions in the README to run the examples from this post or try your own. If you have any questions or comments, tweet at @chromaticHQ!



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