Ansible Tags - Controls Tasks

 Ansible playbook can be a construct of multiple plays or each play may contains multiple tasks. This is where we may have situation where you need to add new task to the existing play or playbook, and we need to test many times that newly added task. 

While testing multiple times we many don't want to execute certain tasks such as a task 'Send email notification' when you preparing a 'Reboot of server' or 'Restart of Service' or 'Deployment of a service'. During the testing time you may want to exclude these notification tasks. 

There are situations where we might want to run a particular task as per the input at the run time of a playbook. This may be from AWX/Tower UI select them.

Ansible tags - to control the tasks of a Playbook

I will be explaining in this post, How to run or not to run a particular task in given  playbook. 

Important concepts about Ansible tags

• Ansible tags are keys to identify and control the tasks for execution or exclude from the playbook that could have multiple tasks
• Ansible tags are references or aliases to a task inside a play selection can be done with -t or --tags options in the command line 
• Selecting a tag for exclude can be defined with --skip-tags option
• A task may have multiple tags such as sending email task could have tags as email_notify, notifications
• There can be same tag that can be associated with multiple tasks such as notifications  can be associated with sending email and sending slack notices as well

Prerequisites

I've Ansible Controller machine and wanted to install the 'Apache2' webserver on the managed nodes. I've a sample playbook for it. 

How to be specific during the execution of Ansible Playbook?

Now let me create a playbook for install and control a Apache webserver. All my managed nodes are with CentOS so I'm using yum package module in this.

The logic for the below playbook is build with two modules: yum, service

staate attribute of yum package module

service module parameter state and values

You can see the YAML using tags which is our main objective of this post:

---
 - name: Install and control Apache Webservers 
   hosts: "{{ targets | default('localhost') }}" 
   become: yes
   tasks: 
     - name: Install httpd server
       yum:
         name: httpd
         state: present 
       tags: install_httpd, boot_web

     - name: start httpd server
       service:
         name: httpd
         state: started 
       tags: start_httpd, boot_web

     - name: stop httpd server
       service: 
         name: httpd
         state: stopped
       tags: stop_httpd, destroy_web

     - name: uninstall httpd server
       yum:
         name: httpd 
         state: absent
       tags: uninstall_httpd, destroy_web

The Package state – parameter values can be found from the ansible documentation The execution can be specific to start the webserver, that means there should be Apache webserver must be installed and then start the service. To install webserver on two nodes.

ansible-playbook httpd-tags.yml -t install_httpd -e targets=ansible-node-1,ansible-nodes-2

To start the webserver on two remote hosts

ansible-playbook httpd-tags.yml -t start_httpd -e targets=ansible-node-1,ansible-nodes-2

Ansible tags passed in the command line with -t option

To install and start webserver if no targets mentioned means it will be localhost where Ansible controller running there this webserver will be installed and started with the following command

ansible-playbook httpd-tags.yml --tags boot_web 

To stop the webserver on two remote hosts

ansible-playbook httpd-tags.yml -t stop_httpd -e targets=ansible-node-1,ansible-nodes-2

To uninstall the webserver on two remote hosts

ansible-playbook httpd-tags.yml -t uninstall_httpd -e targets=ansible-node-1,ansible-nodes-2

We can also select multiple tags to run the playbook. To stop the webserver on two remote hosts

ansible-playbook httpd-tags.yml -t stop_httpd,uninstall_httpd -e targets=ansible-node-1,ansible-nodes-2

Ansible tags using multiple tags

Same thing can be executed with excluding tasks which we can tell by using --skip-tags options for the install_httpd, start_httd means remaining tasks need to be executed.

ansible-playbook httpd-tags.yml --skip-tag install_httpd,start_httpd -e targets=ansible-node-1,ansible-nodes-2

We can also use common tag instead of using two tags used for stop and uninstall the webserver as destroy_web single tag.

ansible-playbook httpd-tags.yml --tags destroy_web 

Hey is there any other alternative way without tags can I say from here onwards execute the playbook?

Yes, We can also use task-name as an input for a special option –start-at-task for the ansible-playbook command. See this example that tells 'stop httpd server' onwards means two tasks will be executed that is stop_httpd, uninstall_httpd tasks.

ansible-playbooks httpd_tags.yml --start-at-task "stop httpd server"

There are two newly introduced from Ansible 2.5 version onwards they are important and very special tags in Ansible playbooks are always and never.

Always: If you assign the always to tag to a task or play then Ansible Controller will always run that task or play unless you specify that need to be skip using --skip--tags

Never: If you assign the never tag to a task or play then Ansible controller will skip that particular task or play unless you specify with '--tags never' it looks odd! But it works as it meant to do in that way.

 

---
- name: Understanding always, never tags
  hosts: localhost
  become: true
  tasks:
    - name: Tasks execute always 
      command: echo "this is from always tag"
      tags:
        - always

    - name: Install nginx server
      apt:
        name: "nginx"
        state: "present"
      tags:
        - install
        - never

    - name: Deploy webpage to website
      copy:
        src: index.html
        dest: /var/www/html/
      tags:
        - deploy
  

When you run this playbook it will always task will be executed always! The install task will be never executed. What is the command to list all tags present in a Playbook?

ansible-playbook mytags.yml --list-tags
  

Terminology: AWX is free open-source project that enables us to manage Ansible from a web interface.

All the examples executed thanks to Krishna

Courtesy by   Krishna Tatipally

Document References:

1. yum module
2. service module
3. tags management in Ansible

Ansible packages and service modules

Ansible packages and service modules In this post I would like to take you to the most important Linux administration tasks which can be used regularly in their daily activities that can be automated with Ansible. 

How do Linux Package Managers works?

Every Linux Operating system allow us to install any software using package managers such as yum, dnf, apt, deb or apk any other option. 

Here I've explored more details about this package mangers how they are working. If we take RedHat flavor Linux systems such as CentOS, SuSe, RHEL uses actually RPM as package manager. But the CLI clients are available such as yum(Yellowdog updater modified) and in the latest versions using improved yum that is dnf command utility which is known as "Dandified Yum". 

The service or systemctl commands

After installation we need to start, stop or restart or check status that service using systemctl or service command as per the System availability.

Ansible package manager modules connection with front-backend utilities

 
First we will experiment with package managers dnf usage in Ansible. We can target simple two playbooks where you should have inventory groups defined for webserver, database.

Prerequisite:

The inventory file content with the webserver and database groups as following

[ansible@master qa]$ cat hostqa.yml

all:
  children:
    qa:
      children:
        qawebserver:
          hosts:
            node[1:2]-vt:
        qadbserver:
          hosts:
            node3-vt:
        qalb:
          hosts:
            node4-vt:

How to install packages using ansible yum module?

The Ansible yum module is allow us to install the packages on the target hosts. where you can tell the action using state.

---
# File: nginx_yum_installation.yml

- name: install and start nginx
  hosts: "{{ targets | default ('webserver') }}"
  become: yes
  tasks:
    - name: install nginx
      yum:
        name: nginx
        state: present
        update_cache: true

    - name: start nginx
      service:
        name: nginx
        state: started

  

The execution of the above playbook output as:

ansible-playbook nginx_yum_installation.yml
  

Ansible yum module for install nginx and start the service

How to uninstall package using ansible yum module?

The following ansible playbook code will stop the service and remove the package from the target box.

  ---
# Filename: nginx_stop_yumremove.yml
- name: stop and remove nginx
  hosts: "{{ targets | default('localhost') }}"
  become: yes
  gather_facts: no
  tasks:
    - name: stop nginx server
      service:
        name: nginx
        state: stopped

    - name: remove nginix
      yum:
        name: nginx
        state: absent

  

Execution outcome

   ansible-playbook -e targets=qawebserver nginx_stop_yumremove.yml --check
   ansible-playbook -e targets=qawebserver nginx_stop_yumremove.yml 
  

Ansible yum module to remove nginx package

How to install packages using ansible apt module?

The Ansible apt module is allow us to install the packages on the target hosts. where you can tell the action using state.

  ---
# Filename: nginx_apt_installation.yml

- name: install and start nginx
  hosts: "{{ targets | default ('loadbalancer') }}"
  become: yes
  tasks:
    - name: install nginx
      apt:
        name: nginx
        state: present
        update_cache: false

    - name: start nginx
      service:
        name: nginx
        state: started
  

The execution of the above playbook output as:

ansible-playbook nginx_apt_installation.yml
  

How to install a package with ansible dnf module?

If you are working on CentOs8 or Oracle Linux 8 or RHEL 8 then you can use dnf module. The web group target to install nginx webserver, and database target to install with mysql database.

---
- hosts: webserver
  tasks:
    - name: install nginx
      dnf: name=nginx state=present update_cache=true
  

Package manager module can be executed on the target machine with ansible user generally, but it requires sudo access so we need to use become parameter value as 'yes'. In adhoc command execution we can use -b or --become option.

ansible webserver -m yum -a "name=httpd state=latest" -b

How to list out the package is installed?

The yum module can be used to determine if a package is available and installed on the managed node (e.g. the target VM). This ansible module execution is similar to the `yum info` command in CLI. Let's examine "nginx" installed on the web boxes with the followng playbook.

- name: List out the yum installed packages
  hosts: "{{ targets | default ('loadbalancer') }}"
  gather_facts: false
  #remote_user: root
  become: yes
  tasks:
    - name: determine if a package is installed
      yum:
        list: "{{ package }}"
      register: out

    - debug:
        msg:
          - "package: {{ package }}"
          - "yumstate: {{ out.results[0].yumstate }}"
          - "yumstate: {{ out.results[1].yumstate }}"
          - "version: {{ out.results[1].version }}"

		

Executed with the following command :

ansible-playbook -e targets=node1-vt -e package=nginx yum_list.yml

The screen screen will look like this:

Ansible yum module listing out about a package

  To check already httpd is installed on a machine:

rpm -qa|grep httpd 

Important Note:

The name very first you defined used hyphen, here hyphen is only used when you want general information for the playbook reader to indicate about the task. when we use module attribute with name should not with hyphen.

References Ansible documentation:

1. Package manger - dnf  

2. Package manager - apt  

3. Package manager - yum 

4. default target in ansible