L3 Task Execution management

1. Defining task execution with host groups

task2-1.yaml

---
- hosts: all
  tasks:
  - name: create tmp folder on all servers
    file:
      dest: $HOME/tmp/
      state: directory


- hosts: all
  tasks:
  - name: create a file on a remote machine
    file:
      dest: $HOME/tmp/file
      state: '{{file_state}}'

- hosts: web
  tasks:
  - name: create file on web machines
    file:
      dest: $HOME/tmp/web-file
      state: '{{file_state}}'

- hosts: all:!db
  tasks:
  - name: create file on web machines
    file:
      dest: $HOME/tmp/web-not-db-file
      state: '{{file_state}}'

- hosts: all:&backup:!web
  tasks:
  - name: create file on web machines
    file:
      dest: $HOME/tmp/backup-file
      state: '{{file_state}}'

# operators '& and' and '! not'
# Set "file_state" as variable passed in  '{{file_state}}'

• operators '& and' and '! not'
• Set "file_state" as variable passed in '{{file_state}}'

1-1 file.state: directory

If directory, all intermediate subdirectories will be created if they do not exist. Since Ansible 1.7 they will be created with the supplied permissions.

1-2 file.state: '{{file_state}}'

• File module: https://docs.ansible.com/ansible/latest/modules/file_module.html#file-module

• once with the state of touch, create this file if it doesn't exist

• Seoncd time, we'll run it with the state of absent

1-3 hosts: all:!db and all:&backup:!web

• operators '& and' and '! not'
• Set "file_state" as variable passed in '{{file_state}}'

1-4 Touch file

#!/bin/bash
ansible-playbook -i ../inventory.ini task2-1.yaml -e file_state=touch

• -e EXTRA_VARS, set additional variables as key=value or YAML/JSON, if filename prepend with @

• If touch (new in 1.4), an empty file will be created if the path does not exist, while an existing file or directory will receive updated file access and modification times, (similar to the way touch works from the command line).

1-5 Delete file

#!/bin/bash
ansible-playbook -i ../inventory.ini task2-1.yaml -e file_state=absent

• If absent, directories will be recursively deleted, and files or symlinks will be unlinked.

• Note that absent will not cause file to fail if the path does not exist as the state did not change.

2. Using tags to limit play execution

task2-2-tag.yaml

---
- hosts: all
  tasks:
  - name: create a file
    file:
      dest: $HOME/tmp/file
      state: touch
    tags:
      - create-file

- hosts: all:k8s_servers:!db
  tags:
    - delete-file
  tasks:
  - name: delete a file
    file:
      dest: $HOME/tmp/file
      state: absent

- hosts: web:githost
  tasks:
  - name: delete a file
    file:
      dest: /tmp/file
      state: absent
    tags:
      - delete-file

- hosts: all
  tags:
    - list-file
  tasks:
  - name: Recursively find /tmp files
    find:
      paths: $HOME/tmp/
      recurse: yes
    register: all_files

  - debug:
      msg: "{{ all_files.files[0].path }}"

2-1 Add tags

- name: delete a file
  file:
    dest: $HOME/tmp/file
    state: absent

tags:
  - create-file

- hosts: all:k8s_servers:!db
  tags:
    - delete-file

2-2 Take advantage tags

$ ansible-playbook -i ../inventory.ini task2-2-tag.yaml --skip-tags create-file --tags delete-file

$ ansible-playbook -i ../inventory.ini task2-2-tag.yaml --tags create-file


PLAY RECAP *********************************************************************************************************************************************
githost                    : ok=3    changed=1    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   
k8s-jx                     : ok=3    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   

Tags

When you execute a playbook, you can filter tasks based on tags in two ways:

On the command line, with the --tags or --skip-tags options

ansible-playbook -i ../inventory.ini task2-2-tag.yaml --skip-tags create-file --tags delete-file

• --tags or --skip-tags can be used both or just one

2-3 List files in directory

- hosts: all
  tags:
    - list-file
  tasks:
  - name: Recursively find /tmp files
    find:
      paths: $HOME/tmp/
      recurse: yes
    register: all_files

  - debug:
      msg: "{{ all_files.files[0].path }}"

Show output

- debug:
      msg: "{{ all_files.files[0].path }}"

TASK [debug] *******************************************************************************************************************************************
ok: [githost] => {
    "msg": "/home/vagrant/tmp/file"
}
ok: [k8s-jx] => {
    "msg": "/home/vagrant/tmp/file"
}
ok: [k8s-jx1] => {
    "msg": "/home/vagrant/tmp/file"
}
ok: [k8s-jx2] => {
    "msg": "/home/vagrant/tmp/file"
}

PLAY RECAP *********************************************************************************************************************************************
githost                    : ok=5    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   
k8s-jx                     : ok=5    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   
k8s-jx1                    : ok=4    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   
k8s-jx2                    : ok=4    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   

3. Executing tasks on localhost

3-1 You dont have to create host for localhost ininventory.ini

---
- hosts: localhost
  tasks:
  - name: Create a file via ssh connection
    file:
      dest: $HOME/Devops_sap/ansible/code/task2/2-3ssh-created
      state: touch

- hosts: localhost
  connection: local

  tasks:
  - name: Create a file via sdirect local connection
    file:
      dest: $HOME/Devops_sap/ansible/code/task2/2-3direct-created
      state: touch

4. Limiting plays from the command line

---
- hosts: all
  tasks:
  - name: the first task
    file:
      dest: $HOME/tmp/first-task
      state: '{{file_state}}'
  - name: the second task
    file:
      dest: $HOME/tmp/second-task
      state: '{{file_state}}'
  - name: the last task
    file:
      dest: $HOME/tmp/last-task
      state: '{{file_state}}'

4-1 execute from Start and Step by name

$ ansible-playbook -i ../inventory.ini task2-4-limit.yaml -e file_state=touch --start-at-task='the second task'

$ ansible-playbook -i ../inventory.ini task2-4-limit.yaml -e file_state=touch --start-at-task='the second task'

--start-at-task='the second task'

5. Specifying variables via inventory

When we start an Ansible run, one of the very first things that we see is that Ansible wants to gather facts from a host. This is effectively a set of variables that we can consume in our playbooks to make certain actions happen on a host-by-host basis.

A very powerful tool. We also find though that sometimes we want to pass specific variables on a host-by-host or group-by-group basis, sort of extending the function of what the inventory provides.

5-1 2-5-invetory.ini

...

[backup]
k8s-jx2 backup_file=$HOME/tmp/backup_file

[all:vars]
all_file=$HOME/tmp/all_file

[web:vars]
web_file=$HOME/tmp/web_file

• [all:vars]
• [web:vars]

5-2 task2-5-var.yaml

---
- hosts: web
  tasks:
  - name: create a web file
    file:
      dest: '{{web_file}}'
      state: '{{file_state}}'

- hosts: backup
  tasks:
  - file:
      dest: '{{backup_file}}'
      state: '{{file_state}}'


- hosts: db
  tasks:
  - file:
      dest: '{{db_file}}'
      state: '{{file_state}}'
    when: db_file is defined 

- hosts: all
  tasks:
  - file:
      dest: '{{all_file}}'
      state: '{{file_state}}'

5-3 when

when: db_file is defined

• 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.

• check db_file is defined: https://medium.com/opsops/is-defined-in-ansible-d490945611ae

**5-4 Run the command **

$ ansible-playbook -i ../2-5-inventory.ini task2-5-var.yaml -e file_state=touch
$ ansible-playbook -i ../2-5-inventory.ini task2-5-var.yaml -e file_state=absent

Becasue the db_file is not defined

TASK [file] *************************************************************************
skipping: [k8s-jx1]
skipping: [k8s-jx2]

...

k8s-jx1   : ok=3    changed=0    unreachable=0    failed=0    skipped=1    rescued=0    ignored=0   
k8s-jx2   : ok=5    changed=0    unreachable=0    failed=0    skipped=1    rescued=0    ignored=0