This is a very important execution strategy where one needs to execute only one execution and not the entire playbook. For example, suppose you only want to stop a server (in case a production issue comes) and then post applying a patch you would like to only start the server.

Here in original playbook stop and start were a part of different roles in the same playbook but this can be handled with the usage of tags. We can provide different tags to different roles (which in turn will have tasks) and hence based on the tags provided by the executor only that specified role/task gets executed. So for the above example provided, we can add tags like the following −

– {role: start-tomcat, tags: [‘install’]}}

The following command helps in using tags −

ansible-playbook -i hosts <your yaml> –tags “install” -vvv

With the above command, only the start-tomcat role will be called. The tag provided is case-sensitive. Ensure exact match is being passed to the command.

How to Limit Execution by Hosts

There are two ways to achieve the execution of specific steps on specific hosts. For a specific role, one defines the hosts – as to which specific hosts that specific role should be run.

Example

- hosts: <A>
environment: "{{your env}}"
pre_tasks:
- debug: msg = "Started deployment.
Current time is {{ansible_date_time.date}} {{ansible_date_time.time}} "
roles:
- {role: <your role>, tags: ['<respective tag>']}
post_tasks:
- debug: msg = "Completed deployment.
Current time is {{ansible_date_time.date}} {{ansible_date_time.time}}"
- hosts: <B>
pre_tasks:
- debug: msg = "started....
Current time is {{ansible_date_time.date}} {{ansible_date_time.time}} "
roles:
- {role: <your role>, tags: ['<respective tag>']}
post_tasks:
- debug: msg = "Completed the task..
Current time is {{ansible_date_time.date}} {{ansible_date_time.time}}"

As per the above example, depending on the hosts provided, the respective roles will only be called. Now my hosts A and B are defined in the hosts (inventory file).

Alternate Solution

A different solution might be defining the playbook’s hosts using a variable, then passing in a specific host address via –extra-vars −

# file: user.yml  (playbook)
---
- hosts: '{{ target }}'
user: ...

playbook contd….

Running the Playbook

ansible-playbook user.yml --extra-vars "target = "<your host variable>"

If {{ target }} isn’t defined, the playbook does nothing. A group from the hosts file can also be passed through if need be. This does not harm if the extra vars is not provided.

Playbook targeting a single host

$ ansible-playbook user.yml --extra-vars "target = <your hosts variable>" --listhosts

So, this brings us to the end of blog. This Tecklearn ‘Concept of Advanced Execution with Ansible’ blog helps you with commonly asked questions if you are looking out for a job in DevOps. If you wish to learn Ansible and build a career in DevOps domain, then check out our interactive, Configuration Management using Ansible Training, that comes with 24*7 support to guide you throughout your learning period. Please find the link for course details:

https://www.tecklearn.com/course/configuration-management-using-ansible/

Configuration Management using Ansible Training

About the Course

Tecklearn has specially designed this Configuration Management using Ansible Training Course to advance your skills for a successful career in this domain. The course will cover different components of Ansible and how they are used in software development operations. You will get an in-depth knowledge of these concepts and will be able to work on related demos. Upon completion of this online training, you will hold a solid understanding and hands-on experience with Ansible.

Why Should you take Configuration Management using Ansible Training?

The average Ansible salary in USA is $136,500 per year or $70 per hour. Entry level positions start at $100,000 per year while most experienced workers make up to $187,500 per year.
Wells Fargo, Capital One, Apple, CISCO & many other MNC’s worldwide use Ansible across industries.
According to Grand View Research, the DevOps market size is estimated to be worth $12.85 billion by 2025. DevOps professionals are highly paid and in-demand throughout industries including retail, eCommerce, finance, and technology.

What you will Learn in this Course?

Introduction to DevOps

What is Software Development
Software Development Life Cycle
Why DevOps?
What is DevOps?
DevOps Lifecycle
DevOps Tools
Benefits of DevOps
How DevOps is related to Agile Delivery
DevOps Implementation

Configuration Management using Ansible

What is Ansible?
Ansible vs Puppet
Ansible Architecture
Ansible Installation
Setting up Master Slave using Ansible
Configuring Ansible Roles
Write Playbooks
Applying configuration using Ansible
Hands on

Got a question for us? Please mention it in the comments section and we will get back to you.

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