Book Image

Mastering Ansible - Fourth Edition

By : James Freeman, Jesse Keating
Book Image

Mastering Ansible - Fourth Edition

By: James Freeman, Jesse Keating

Overview of this book

Ansible is a modern, YAML-based automation tool (built on top of Python, one of the world’s most popular programming languages) with a massive and ever-growing user base. Its popularity and Python underpinnings make it essential learning for all in the DevOps space. This fourth edition of Mastering Ansible provides complete coverage of Ansible automation, from the design and architecture of the tool and basic automation with playbooks to writing and debugging your own Python-based extensions. You'll learn how to build automation workflows with Ansible’s extensive built-in library of collections, modules, and plugins. You'll then look at extending the modules and plugins with Python-based code and even build your own collections — ultimately learning how to give back to the Ansible community. By the end of this Ansible book, you'll be confident in all aspects of Ansible automation, from the fundamentals of playbook design to getting under the hood and extending and adapting Ansible to solve new automation challenges.
Table of Contents (18 chapters)
Section 1: Ansible Overview and Fundamentals
Section 2: Writing and Troubleshooting Ansible Playbooks
Section 3: Orchestration with Ansible

Serializing single tasks

Certain applications that run multiple copies of a service may not react well to all of those services being restarted at once. Typically, when upgrading this type of application, a serial play is used. However, if the application is of a large enough scale, serializing the entire play may be wildly inefficient. A different approach can be used, which is to serialize only the sensitive tasks (often the handlers to restart services).

To serialize a specific handler task, we can make use of a built-in variable, play_hosts. This variable holds a list of hosts that should be used for a given task as a part of the play. It is kept up to date with hosts that have failed or are unreachable. Using this variable, we can construct a loop to iterate over each host that could potentially run a handler task. Instead of using the item value in the module arguments, we'll use the item value in a when conditional...