Ansible Pre Tasks and Post Tasks Example | Devops Junction

In this article, we are going to see how to use ansible pre tasks and post tasks with examples.

What is Ansible pre_tasks?

Ansible pretask is a conditional execution block that runs before running the play. It can be a task with some prerequisites check (or) validation

Some examples we can think where ansible pre-task would be helpful

• To install dependency packages before running the actual application npm install or pip install -r requirements.txt
• To validate if the environment meets sufficient criteria like memory, OS version etc before installing a software
• configuring SSH key prior so that you can log in
• Server provisioning steps like creating user, group etc before the installation or setup begin

There are more examples we can continue adding to this list

To put it simply. If you want to run anything as a prerequisite or prevalidation before your actual play. ansible pre_tasks is your way to go

What is Ansible post_tasks?

Just like ansible pre_tasks but this is executed after the actual play or task is completed.

this is mostly useful for post validation or assertion to make sure things are in the right shape or the result is matching our expectations.

Some examples we can think of are listed below

• To validate if things were installed properly and the playbook executed fine.
• To send emails or Slack notifications after successful completion of a playbook
• Running some other task or for accessing some API or external service upon playbook completion like webhook
• Starting the application after the installation and configuration is completed

We can keep this list going with more and more use cases for ansible post_tasks

Simply put, ansible post_tasks is to conditionally execute a block or play upon the successful completion of the playbook. it can be used for post validation, post-execution automation.

How to use pre_tasks and post_tasks in Ansible

Let us see how to use ansible pre_tasks and post_tasks in the ansible-playbook practically.

In this playbook, we are going to perform the following tasks

• • Install necessary commands and tools using apt module - pre_tasks
  • Validate the nodejs installation is successful and print version using debug and assert
  • Create a directory to download the nodejs application
  • Download the nodejs codebase from GIT repo using Tokenized URL
  • Tokens are saved and retrieved from the Secrets file named gitsecrets.yml
  • Do npm installonce the code is downloaded
  • Start the nodejs application
  • Validate if the port is open and Node js is accepting requests
  • Send Slack notification using ansible slack module - post_tasks

---
  - name: Install and Launch the Simple NodeJS Application
    hosts: testserver
    vars_files:
       - gitsecrets.yml
    vars:
       - destdir: /apps/sampleapp

    pre_tasks:
      - name : install dependencies before starting
        become: yes
        register: aptinstall
        apt:
           name: 
            - nodejs
            - npm
            - git
           state: latest
           update_cache: yes
      
      - name : validate the nodejs installation
        debug: msg="Installation of node is Successfull"
        when: aptinstall is changed
    
    tasks:
       - name: Version of Node and NPM
         shell:
            "npm -v && nodejs -v"
         register: versioninfo

       - name: Validate if the installation is intact
         assert:
          that: "versioninfo is changed"

      
       - name: Create Dest Directory if not exists
         become: yes
         file: 
          path: "{{ destdir }}"
          state: directory
          owner: vagrant
          group: vagrant
          mode: 0755

       - name: Download the NodeJS code from the GitRepo
         become: yes
         git:
            repo: 'https://{{gittoken}}@github.com/AKSarav/SampleNodeApp.git'
            dest: "{{ destdir }}"

       - name: Change the ownership of the directory
         become: yes
         file:
           path: "{{destdir}}"
           owner: "vagrant"
         register: chgrpout

       - name: Install Dependencies with NPM install command
         shell:
            "npm install"
         args:
            chdir: "{{ destdir }}"
         register: npminstlout

       - name: Debug npm install command
         debug: msg='{{npminstlout.stdout_lines}}'


       - name: Start the App
         async: 10
         poll: 0
         shell:
            "(node index.js > nodesrv.log 2>&1 &)"
         args:
           chdir: "{{ destdir }}"
         register: appstart

       - name: Validating the port is open
         tags: nodevalidate
         wait_for:
           host: "localhost"
           port: 5000
           delay: 10
           timeout: 30
           state: started
           msg: "NodeJS server is not running"

    post_tasks:
        - name: notify Slack that the servers have been updated 
          tags: slack
          community.general.slack:
            token: T026******PF/B02U*****N/WOa7r**********Ao0jnWn
            msg: |
                ### StatusUpdate ###
                – ------------------------------------
                ``
                `Server`: {{ansible_host}}
                `Status`: NodeJS Sample Application installed successfully
                – ------------------------------------
            channel: '#ansible'
            color: good
            username: 'Ansible on {{ inventory_hostname }}'
            link_names: 0
            parse: 'none'
          delegate_to: localhost

You can see how we are using pre_tasks and post_tasks in this playbook

we are using pre_tasks to run a task that installs necessary components and packages like node, npm etc

Learn more about, how to use apt with ansible.

and using post_tasks to send a notification to the Slack channel upon Task completion using the ansible slack module and webhook. I will try to cover this slack integration in detail in my next article

Here is the output of this playbook

$ ansible-playbook install-nodejs-app.yaml -i hosts – ask-vault-password
Vault password: 

PLAY [Install and Launch the Simple NodeJS Application] ************************************************************************************

TASK [Gathering Facts] *********************************************************************************************************************
ok: [testserver]

TASK [install dependencies before starting] ************************************************************************************************
changed: [testserver]

TASK [validate the nodejs installation] ****************************************************************************************************
ok: [testserver] => {
    "msg": "Installation of node is Successfull"
}

TASK [Version of Node and NPM] *************************************************************************************************************
changed: [testserver]

TASK [Validate if the installation is intact] **********************************************************************************************
ok: [testserver] => {
    "changed": false,
    "msg": "All assertions passed"
}

TASK [Create Dest Directory if not exists] *************************************************************************************************
changed: [testserver]

TASK [Download the NodeJS code from the GitRepo] *******************************************************************************************
changed: [testserver]

TASK [Change the ownership of the directory] ***********************************************************************************************
ok: [testserver]

TASK [Install Dependencies with NPM install command] ***************************************************************************************
changed: [testserver]

TASK [Debug npm install command] ***********************************************************************************************************
ok: [testserver] => {
    "msg": [
        "nodeproject1@1.0.0 /apps/sampleapp",
        "├─┬ express@4.17.2 ",
        "│ ├─┬ accepts@1.3.7 ",
        "│ │ ├─┬ mime-types@2.1.34 ",
        "│ │ │ └── mime-db@1.51.0 ",
        "│ │ └── negotiator@0.6.2 ",
        "│ ├── array-flatten@1.1.1 ",
        "│ ├─┬ body-parser@1.19.1 ",
        "│ │ ├── bytes@3.1.1 ",
        "│ │ ├─┬ http-errors@1.8.1 ",
        "│ │ │ ├── inherits@2.0.4 ",
        "│ │ │ └── toidentifier@1.0.1 ",
        "│ │ ├─┬ iconv-lite@0.4.24 ",
        "│ │ │ └── safer-buffer@2.1.2 ",
        "│ │ └── raw-body@2.4.2 ",
        "│ ├── content-disposition@0.5.4 ",
        "│ ├── content-type@1.0.4 ",
        "│ ├── cookie@0.4.1 ",
        "│ ├── cookie-signature@1.0.6 ",
        "│ ├─┬ debug@2.6.9 ",
        "│ │ └── ms@2.0.0 ",
        "│ ├── depd@1.1.2 ",
        "│ ├── encodeurl@1.0.2 ",
        "│ ├── escape-html@1.0.3 ",
        "│ ├── etag@1.8.1 ",
        "│ ├─┬ finalhandler@1.1.2 ",
        "│ │ └── unpipe@1.0.0 ",
        "│ ├── fresh@0.5.2 ",
        "│ ├── merge-descriptors@1.0.1 ",
        "│ ├── methods@1.1.2 ",
        "│ ├─┬ on-finished@2.3.0 ",
        "│ │ └── ee-first@1.1.1 ",
        "│ ├── parseurl@1.3.3 ",
        "│ ├── path-to-regexp@0.1.7 ",
        "│ ├─┬ proxy-addr@2.0.7 ",
        "│ │ ├── forwarded@0.2.0 ",
        "│ │ └── ipaddr.js@1.9.1 ",
        "│ ├── qs@6.9.6 ",
        "│ ├── range-parser@1.2.1 ",
        "│ ├── safe-buffer@5.2.1 ",
        "│ ├─┬ send@0.17.2 ",
        "│ │ ├── destroy@1.0.4 ",
        "│ │ ├── mime@1.6.0 ",
        "│ │ └── ms@2.1.3 ",
        "│ ├── serve-static@1.14.2 ",
        "│ ├── setprototypeof@1.2.0 ",
        "│ ├── statuses@1.5.0 ",
        "│ ├─┬ type-is@1.6.18 ",
        "│ │ └── media-typer@0.3.0 ",
        "│ ├── utils-merge@1.0.1 ",
        "│ └── vary@1.1.2 ",
        "└─┬ redis@4.0.2 ",
        "  ├── @node-redis/bloom@1.0.1 ",
        "  ├─┬ @node-redis/client@1.0.2 ",
        "  │ ├── cluster-key-slot@1.1.0 ",
        "  │ ├── generic-pool@3.8.2 ",
        "  │ ├─┬ redis-parser@3.0.0 ",
        "  │ │ └── redis-errors@1.2.0 ",
        "  │ └── yallist@4.0.0 ",
        "  ├── @node-redis/json@1.0.2 ",
        "  ├── @node-redis/search@1.0.2 ",
        "  └── @node-redis/time-series@1.0.1 "
    ]
}

TASK [Start the App] ***********************************************************************************************************************
changed: [testserver]

TASK [Validating the port is open] *********************************************************************************************************
ok: [testserver]

TASK [notify Slack that the servers have been updated] *************************************************************************************
ok: [testserver -> localhost]

PLAY RECAP *********************************************************************************************************************************
testserver                 : ok=13   changed=6    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

Conclusion

In this article, we have learnt what is ansible pre tasks and ansible post tasks and how to use them.

As a summary, we learnt pre_tasks is to execute some tasks prior/before executing the actual play or tasks. there can be many tasks under pre_tasks

Likewise, ansible post_tasks is to execute some tasks post/after the successful completion of the actual play or tasks. Like sending emails and slack notifications etc.

We have also learned how to send slack notifications using ansible post_task in this article along with a few more tricks like

• Ansible Assertion
• Ansible Git
• How to use ansible wait_for
• how to install packages with Ansible apt
• Ansible Shell.
• How to use Ansible Vault and secrets in the playbook

We have around 50+ articles dedicatedly for each of these modules. in DevopsJunction.

Please refer to the following article and make use of it.

Ansible Playbook Examples – Sample Ansible Playbooks | Devops Junction

Cheers
Sarav AK

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