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L4 Ansible Variable Management

1. Jinja and templates

template – Template a file out to a remote server

Templates are processed by the Jinja2 templating language.

1-1 task2-8jinja2.yaml

---
- hosts: all
  tasks:
  - name: deploy a simple template file
    template:
      src: templates/2-8-template.j2
      dest: $HOME/tmp/2-8-template.txt
    tags:
      - create
  - name: remove templated file
    file:
      dest: $HOME/tmp/2-8-template.txt
      state: absent
    tags:
      - destroy

1-2 templates/2-8-template.j2

This file is a template on {{hostvars[inventory_hostname]['ansible_fqdn']}}
backup_file {% if backup_file is defined %} is defined {% else %} is not defined {% endif %}

$ ansible-playbook -i ../inventory.ini task2-8jinja2.yaml --tags create

TASK [deploy a simple template file] *****************************************************
changed: [githost]
changed: [k8s-jx]
changed: [k8s-jx2]
changed: [k8s-jx1]

PLAY RECAP *******************************************************************************
githost                    : ok=2    changed=1    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   
k8s-jx                     : ok=2    changed=1    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   
k8s-jx1                    : ok=2    changed=1    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   
k8s-jx2                    : ok=2    changed=1    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

jabox

This file is a template on jabox
backup_file  is not defined

jabox-node1

This file is a template on jabox-node1
backup_file  is not defined

jabox-node2

This file is a template on jabox-node2
backup_file  is not defined

ansible-playbook -i ../inventory.ini task2-8jinja2.yaml --tags destroy

2. Host facts for conditional execution

---
- hosts: web
  tasks:
  - name: create
    file:
      dest: $HOME/tmp/k8s-master-on-githost 
      state: '{{file_state}}'
    when: hostvars[inventory_hostname]['inventory_hostname'] == 'githost'  
#where the file gonna be created

  - name: create
    file:
      dest: $HOME/tmp/githost-on-k8s-master
      state: '{{file_state}}'
    when: inventory_hostname == 'k8s-jx' 
#where the file gonna becreated

2-1 Conditionals

Sometimes you will want to skip a particular step on a particular host.

This could be something as simple as not installing a certain package if the operating system is a particular version, or it could be something like performing some cleanup steps if a filesystem is getting full.

This is easy to do in Ansible with the when clause, which contains a raw Jinja2 expression without double curly braces. It’s actually pretty simple:

---
- hosts: web
  tasks:
  - name: create
    file:
      dest: $HOME/tmp/k8s-master-on-githost 
      state: '{{file_state}}'
    when: hostvars[inventory_hostname]['inventory_hostname'] == 'githost'  #where the file gonna be created

  - name: create
    file:
      dest: $HOME/tmp/githost-on-k8s-master
      state: '{{file_state}}'
    when: inventory_hostname == 'k8s-jx' #where the file gonna becreated
  • when: hostvars[inventory_hostname]['inventory_hostname']
  • when: inventory_hostname == 'k8s-jx'
ansible -m debug -i ../inventory.ini -a "var=hostvars['k8s-jx1']" k8s-jx2

2-2 debug module

This is information that I could use on the k8s-jx2 host, basically in k8s-jx2 host plays, but that's coming from k8s-jx1. gather k8s-jx2 fact from all ther machine

ansible-playbook -i ../inventory.ini task2-9fact.yaml -e file_state=touch

TASK [create] ****************************************************************************************
skipping: [k8s-jx]
changed: [githost]

TASK [create] ****************************************************************************************
skipping: [githost]
changed: [k8s-jx]

PLAY RECAP *******************************************************************************************
githost                    : ok=2    changed=1    unreachable=0    failed=0    skipped=1    rescued=0    ignored=0   
k8s-jx                     : ok=2    changed=1    unreachable=0    failed=0    skipped=1    rescued=0    ignored=0
  • On githost: k8s-master-on-githost
  • On k8s-master: githost-on-k8s-master
ansible-playbook -i ../inventory.ini task2-9fact.yaml -e file_state=absent

3. Looping tasks with variable lists

3-1 task2-10loopvar.yaml

---
- hosts: all
  vars:
    packages: [git,vim,ruby]
  tasks:
  - name: install packages for Debian style OSs
    apt:
      name: '{{item}}'
      state: '{{pkg_state}}'
    with_items: '{{packages}}'
    when: ansible_os_family == "Debian"
    sudo: yes
    tags:
      - handle-pkg

  - name: install pacakges for Redhat style OSs
    yum:
      name: '{{item}}'
      state: '{{pkg_state}}'
    with_items: '{{packages}}'
    when: ansible_os_family == "RedHat"
    sudo: yes
    tags:
      - handle-pkg

  - name: create files based on package names
    file:
      dest:  $HOME/tmp/{{item}}
      state: '{{file_state}}'
    with_items: '{{packages}}'
    when: ansible_os_family == "RedHat"
    tags:
      - handle-files

$ ansible-playbook -i ../inventory.ini task2-10loopvar.yaml -e file_state=touch -e  pkg_state=latest
$ ansible-playbook -i ../inventory.ini task2-10loopvar.yaml -e file_state=absent -e  pkg_state=absent

$ ansible-playbook -i ../inventory.ini task2-10loopvar.yaml --skip-tags handle-pkg --tags handle-files -e file_state=absent
  • ansible list variable
vars:
    packages: [git,vim,ruby]
  • Loops in ansible

with_items is replaced by loop and the flatten filter.

loop: "{{ items|flatten(levels=1) }}"

with_items: '{{packages}}'
  • ansible_os_family

https://riptutorial.com/ansible/example/12268/-when--condition----ansible-os-family--lists

  • when: ansible_os_family == "CentOS"
  • when: ansible_os_family == "Redhat"
  • when: ansible_os_family == "Darwin"
  • when: ansible_os_family == "Debian"

  • when: ansible_os_family == "Windows"

  • sudo: yes

https://docs.ansible.com/ansible/latest/user_guide/become.html#understanding-privilege-escalation

  • apt.state: and yum.state:

yum state: absent, installed, latest, present, removed

Whether to install (present or installed, latest), or remove (absent or removed) a package.

present and installed will simply ensure that a desired package is installed.

latest will update the specified package if it's not of the latest available version.

absent and removed will remove the specified package.

Default is None, however in effect the default action is present unless the autoremove option is enabled for this module, then absent is inferred.

# [DEPRECATION WARNING]: Invoking "apt" only once while using a loop via squash_actions is deprecated. Instead of using a loop to supply multiple 
# items and specifying `name: "{{item}}"`, please use `name: '{{packages}}'` and remove the loop. This feature will be removed in version 2.11. 
# Deprecation warnings can be disabled by setting deprecation_warnings=False in ansible.cfg.

- name: "Install dependencies"
  apt:
    pkg:
      - libnss3
      - libasound2
      - xcb
      - xinit
    state: present

4. Looping tasks with dictionaries

---
- hosts: all
  vars:
    animals:
      cats:
        tabby:
          color: grey
          persnickityness: high
        calico:
          color: orange
          persnickityness: medium
      dogs:
        doberman:
          color: black
          persnickityness: extreme
        retriever:
          color: golden
          persnickityness: low
  tasks:
  - name: iterate over animal array
    file:
      name: '$HOME/tmp/{{item.key}}-{{item.value.color}}'
      state: '{{file_state}}'
    with_dict: '{{animals.cats}}'

  - name: iterate over animals array
    file:
      name: '$HOME/tmp/{{item.key}}-{{item.value.color}}'
      state: '{{file_state}}'
    with_dict: '{{animals.dogs}}'
    when: 'item.value.persnickityness == "low"'
  • dictionary variable
vars:
  animals:
    cats:
      ...
    dogs:
      ...

  • dict key and value: {{item.key}}-{{item.value.color}}'

  • with_dict: '{{animals.cats}}

  • with_dict: '{{animals.dogs}}'
  • when: 'item.value.persnickityness == "low"'
$ ansible-playbook -i ../inventory.ini task2-11loopdict.yaml -e file_state=touch
$ ansible-playbook -i ../inventory.ini task2-11loopdict.yaml -e file_state=absent

Alphabetical order

calico-orange
retriever-golden
tabby-grey

5. Looping in templates with variable lists

---
- hosts: all
  vars:
    packages: [git,vim,ruby]
  tasks:
  - name: deploy a template file with a loop
    template:
      src: templates/2-12-template.j2
      dest: $HOME/tmp/2-12-template.txt
    tags:
      - create
  - name: remove the templated file
    file:
      dest: $HOME/tmp/2-12-template.txt
      state: absent
    tags:
      - destroy

5-1 templates/2-12-template.j2

We are on host {{inventory_hostname}}
We installed: {% for package in packages %}{{package}}{% if not loop.last %}, {% endif %}{% endfor %}

ansible-playbook -i ../inventory.ini task2-12looptemplist.yaml --tags create
ansible-playbook -i ../inventory.ini task2-12looptemplist.yaml --tags absent

We are on host k8s-jx
We installed: git, vim, ruby

We are on host githost
We installed: git, vim, ruby

6. Looping in templates with dictionaries

---
- hosts: all
  vars:
    animals:
      cats:
        tabby:
          color: grey
          persnickityness: high
        calico:
          color: orange
          persnickityness: medium
      dogs:
        doberman:
          color: black
          persnickityness: extreme
        retriever:
          color: golden
          persnickityness: low
  tasks:
  - name: deploy a dictionary looping template file
    template:
      src: templates/2-13-template.j2
      dest: $HOME/tmp/2-13-template.txt
    tags:
      - create
  - name: remove the templated file
    file:
      dest: $HOME/tmp/2-13-template.txt
      state: absent
    tags:
      - destroy

6-1 templates/2-13-template.j2

We are in groups: {% for group in hostvars[inventory_hostname]['group_names'] %}{{group}}{% if not loop.last %}, {% endif %}{% endfor %}

We like both {% for key,value in animals.items() %}{{key}}{% if not loop.last %} and {% endif %}{% endfor %}

W{% for key,value in animals.items() %}e like{% for animal,name in animals[key].items() %} {{name.color}} {{animal}}s{% if not loop.last %} and{% endif %}{% endfor %}{% if not loop.last %} and w{% endif %}{% endfor %}

$ ansible-playbook -i ../inventory.ini task2-13looptempdict.yaml --tags create
$ ansible-playbook -i ../inventory.ini task2-13looptempdict.yaml --tags destroy

# k8s-jx
# We are in groups: k8s_master, k8s_servers, web
# We like both cats and dogs
# We like grey tabbys and orange calicos and we like black dobermans and golden retrievers

# githost
# We are in groups: githost_servers, web
# We like both cats and dogs
# We like grey tabbys and orange calicos and we like black dobermans and golden retrievers

# k8s-jx1
# We are in groups: db, k8s_servers
# We like both cats and dogs
# We like grey tabbys and orange calicos and we like black dobermans and golden retrievers

# k8s-jx2
# We are in groups: backup, db, k8s_servers
# We like both cats and dogs
# We like grey tabbys and orange calicos and we like black dobermans and golden retrievers

7. Testing plays with check mode

2-14 Check mode Check Mode (“Dry Run”)

When ansible-playbook is executed with --check it will not make any changes on remote systems.

check s a way of validating that our ansible is actually valid in advance of impacting our systems.