Ansible

When software is delivered as a service, it's important that the server and the application running on it are initialized or configured correctly. Sometimes server modules or the application itself will need to be patched or upgraded. This task is more difficult when the service resides in the cloud and is running on multiple servers. What we need is a tool to automate these tasks. This is where Ansible is useful.

Ansible is well known as a configuration tool that can help us put a remote machine into a desired state. But Ansible can do more: deploy applications, orchestrate multiple tasks across multiple machines, run ad-hoc commands. In short, Ansible is a tool that enables Infrastructure-as-Code (IaC).

Ansible is open source and is sponsored by Red Hat.

Discussion

  • What are some typical use cases of Ansible?
    Ansible for automating data collection for evaluating Wi-Fi network performance. Source: Holmberg 2016.
    Ansible for automating data collection for evaluating Wi-Fi network performance. Source: Holmberg 2016.

    The main uses of Ansible are the following:

    • Provisioning: Provision bare-metal servers, VMs, cloud instances, and more.
    • Configuration Management: Centralize configuration and push the same to all machines. This means a consistent environment for your services regardless of the machine.
    • App Deployment: Manage your app's lifecycle easily, from development to production.
    • Continuous Delivery: Create CI/CD pipelines without additional complexity.
    • Security & Compliance: Scan and remediate site-wide security policies.
    • Orchestration: Orchestrate how multiple configurations interact; manage the environment as a whole and not in silos.

    Consider an example of orchestration. A three-tier web app will have app servers, database servers, content servers, load balancers and a monitoring system. Ansible can do a complex cluster-wide rolling update without any downtime. In fact, Ansible enables immutable infrastructure, meaning that we can replace servers without service disruption.

    It's interesting to note that Ansible configuration can be seen as a type of documentation and a solution for disaster recovery.

  • In Ansible, what do mean by "agentless" architecture?
    Ansible pushes configuration rather than requiring hosts to pull. Source: Berder 2015.
    Ansible pushes configuration rather than requiring hosts to pull. Source: Berder 2015.

    To configure a number of host machines, one approach is to install custom programs, called agents, on each of these machines. The system will also have a server or control node that contains the current configuration. Each agent will periodically poll the server to obtain the configuration. The server and agent communicate using a common pre-defined protocol and port. This is otherwise called the pull approach.

    In Ansible, there are no agents. It uses the push approach, whereby the server pushes configuration or commands to the hosts. Hosts are often diverse. Installing agent programs on different OS/platform is a hassle. In Ansible, SSH is used by the server to talk to a host. OpenSSH is widely deployed. It's open source and lightweight.

    What if an agent crashes? What if server and agents have mismatching versions? Some agents have reportedly used 400MB of memory. Ansible's agentless architecture avoids all these issues. We can start managing the hosts with zero bootstrapping.

  • Could you describe some essentials Ansible terms?

    From the complete Ansible Glossary, we describe a few essential terms:

    • Node: Can either be a Control Node or a Managed Node. Ansible is installed on control nodes but not on managed nodes. Managed nodes are also called hosts.
    • Inventory: A list of managed nodes, specified by an inventory file or hostfile. Hosts can be organized into groups for easier scaling.
    • Task: A unit of execution in Ansible. Each task has an associated command and does a single operation unless it has a loop.
    • Playbook: An ordered list of tasks. These are designed to be easy to read, write, share and understand. Playbooks can use variables.
    • Module: Reusable code that Ansible executes and can be invoked by a task. Ansible comes with dozens of out-of-the-box and ready-to-use modules. Modules are typically organized by their purpose: crypto, database, identity, messaging, network, storage, etc.
    • Role: Makes playbooks modular and reusable. These are units of organization in Ansible. A role can apply variables, tasks or handlers to hosts or groups.
  • What's the Ansible architecture?
    Ansible architecture. Source: Red Hat 2019, 2:44.
    Ansible architecture. Source: Red Hat 2019, 2:44.

    Ansible executes on a control node and connects to hosts using SSH by default. Control node can be Linux, MacOS, or even any machine that has Python 2.7 or 3.5+ installed. Nodes need to have either SSH or PowerShell (Windows); and Python 2.6+ or 3.5+ installed. File transfer is done using sftp or scp.

    Hosts to be managed are listed in files called inventory. Modules offer reusable execution code. Playbooks contain step-by-step instructions.

    Configuration and playbooks are stored as YAML files in a well-defined directory layout. YAML is easier to learn than bash scripting. Ansible Tower, the enterprise version of Ansible, allows configuration to be stored in configuration management databases (CMDB), using PostgreSQL or MongoDB.

    It's been said that,

    If Ansible modules are the tools in your workshop, playbooks are your instruction manuals, and your inventory of hosts are your raw material.
  • Could you share some best practices when using Ansible?

    Keep it simple. Think declaratively. Don't write code in playbooks. Since modules abstract away complexity, always check if there's a module to accomplish what you want. Avoid using run commands (command, shell, raw, script), since error and state handling are difficult. Instead, write your own modules.

    Don't ignore errors with ignore_errors: yes since you'll miss unexpected errors as well. Instead use failed_when and other alternatives. Along with roles, use import* and include* statements to logically chunk and reuse Ansible content.

    In the interest of readability, use descriptive names for both plays and tasks. Variable names can collide. Use prefixes to avoid collision and also improve readability, such as, apache_port and tomcat_port rather than just port.

    YAML's native syntax for name-value pairs is name: value. Use this for readability in preference of Ansible's shorthand name=value. The YAML syntax is easier to read and highlighted by editors and IDEs.

    When using the debug module, use the verbosity parameter to suppress debug messages in production.

    Organize your playbooks based on roles. Have separate inventory for staging and production. Define groups based on roles and geography.

    Ansible-Lint and Playbook Best Practices guides can help.
  • Could you point to useful resources to get started with Ansible?
    An introduction to Ansible. Source: Jamison 2015.

    From Ansible's official site, read an overview of Ansible. Learn about setting up SSH keys and running your first commands in the Getting Start guide. There are also a number of useful whitepapers on Ansible.

    To be part of or contribute, read the Ansible Community Guide.

    Ansible Galaxy is a hub for downloading useful roles. Official documentation lists all Ansible modules.

Milestones

2008

While at Red Hat, Michael DeHaan starts Cobbler, a tool to manage Linux server environments including provisioning, managing DNS and DHCP, updating packaging, and more. Since Cobbler is unable to run ad-hoc tasks on remote hosts, Func is invented. The roots of Ansible are in these early tools.

Feb
2012

Ansible begins as project with system administrators and developers being early adopters. An early adopter is Fedora Infrastructure where Puppet is replaced with Ansible. Ansible embraces the "batteries included" philosophy, with folks contributing modules.

Feb
2013

Ansible 1.0 is released. We can now use when_failed and when_changed in playbooks. With v1.2.1 (July 2013), default connection is OpenSSH if it supports ControlPersists; else, fall back to Paramiko.

Aug
2014

Ansible 1.7 is released. It's the first version to support Windows hosts using native PowerShell rather than SSH. On the control node, Python module winrm is used. Though control node can't be Windows, Windows Subsystem for Linux (WSL) bash shell can be used.

Jan
2016

Ansible 2.0 is released.

Sep
2017

Ansible 2.4 is released. For hosts, support for Python 2.4 and 2.5 are dropped. Old include directives are replaced with import (static) and include (dynamic). Keyword order can be used to specify the order in which hosts are processed. Inventory is revamped. The release is updated in July 2018 as v2.4.7.

Mar
2018

Ansible 2.5 is released. It's recommended to use loop keyword instead of with_* style loops. The new syntax is better with filters instead of using complex query or lookup. Two top-level persistent connection types are introduced, network_cli and netconf. Where possible, prefer these over local connections.

2019
Ansible is a popular configuration tool for cloud infrastructure. Source: Sesto 2019.
Ansible is a popular configuration tool for cloud infrastructure. Source: Sesto 2019.

A survey of 786 IT professionals shows that Ansible is popular as a configuration tool for cloud infrastructure. Terraform has the largest growth in adoption.

Sample Code

  • ---
# Source: https://cloudacademy.com/blog/what-is-ansible/
# Accessed: 2019-06-03
# Example showing Apache update and status across web servers
# This playbook has one play with three tasks

- hosts: webservers
  vars:
    http_port: 80
    max_clients: 200
  remote_user: root
  tasks:
  - name: ensure apache is at the latest version
    yum: name=httpd state=latest
  - name: write the apache config file
    template: src=/srv/httpd.j2 dest=/etc/httpd.conf
    notify:
    - restart apache
  - name: ensure apache is running (and enable it at boot)
    service: name=httpd state=started enabled=yes
  handlers:
    - name: restart apache
      service: name=httpd state=restarted
 

References

  1. Ansible. 2017. "Ansible in Depth." Whitepaper, Ansible, Red Hat. Accessed 2019-06-03.
  2. Ansible. 2018. "The Benefits of Agentless Architecture." Whitepaper, Ansible, Red Hat. Accessed 2019-06-03.
  3. Ansible. 2019a. "Use Cases." Ansible, Red Hat. Accessed 2019-06-04.
  4. Ansible. 2019b. "Ansible - Our Story." Ansible, Red Hat. Accessed 2019-06-04.
  5. Ansible Docs. 2019a. "Glossary." Ansible 2.8, May 28. Accessed 2019-06-04.
  6. Ansible Docs. 2019b. "Best Practices." Ansible 2.8, May 28. Accessed 2019-06-04.
  7. Ansible Docs. 2019c. "Working With Playbooks." Ansible 2.8, May 28. Accessed 2019-06-04.
  8. Ansible Docs. 2019d. "Getting Started." Ansible 2.8, May 28. Accessed 2019-06-04.
  9. Ansible Docs. 2019e. "Basic Concepts." Ansible 2.8, May 28. Accessed 2019-06-04.
  10. Ansible Docs. 2019f. "Module Index." Ansible 2.8, May 28. Accessed 2019-06-04.
  11. Ansible Docs. 2019g. "Installation Guide." Ansible 2.8, May 28. Accessed 2019-06-04.
  12. Ansible Docs. 2019h. "Windows Support." Ansible 2.8, May 28. Accessed 2019-06-04.
  13. Ansible Docs. 2019i. "Ansible 2.5 Porting Guide." Ansible 2.8, May 28. Accessed 2019-06-04.
  14. Ansible GitHub. 2018. "Ansible Changes By Release." Commit 737d8a0, September 05. Accessed 2019-06-05.
  15. Ansible GitHub. 2019a. "ansible/ansible." Commit 87422ea, June 03. Accessed 2019-06-03.
  16. Ansible GitHub. 2019b. "Ansible 2.5 "Kashmir" Release Notes." Commit 4ad6924, February 21. Accessed 2019-06-05.
  17. Appnel, Timothy. 2016. "Ansible Best Practices: The Essentials." The Inside Playbook Blog, Red Hat Ansible, August 31. Accessed 2019-06-03.
  18. Berder, Ronan. 2015. "Getting Started With Ansible in 5 Minutes." Wiredcraft, March 30. Accessed 2019-06-04.
  19. DeHaan, Michael. 2012. "Ansible - A Simple Model-Driven Configuration Management and Command Execution Framework." High Scalability, April 18. Accessed 2019-06-03.
  20. DeHaan, Michael. 2013. "The Origins of Ansible." Blog, Ansible, December 08. Accessed 2019-06-04.
  21. Dober, Kat. 2018. "New to Ansible? Check Out Our Best Practices Guide." New Relic, May 09. Accessed 2019-06-03.
  22. Goossens, Niels. 2017. "A (very) Short Comparison of Ansible, Chef, Puppet and SaltStack." LinkedIn Pulse, September 08. Accessed 2019-06-03.
  23. Holmberg, Frederik. 2016. "Measuring wireless performance using Ansible, Elastic Stack and MikroTik." March 30. Accessed 2019-06-04.
  24. Jamison, Creston. 2015. "Ansible Introduction." Ruby Tree Software, Inc., via YouTube, February 24. Accessed 2019-06-03.
  25. Modine, Austin. 2008. "Cobbler pieces together mass Red Hat Linux installations." The Register, June 19. Accessed 2019-06-03.
  26. Raun, Corban. 2015. "Lessons from using Ansible exclusively for 2 years." Blog, Server Density, March 24. Accessed 2019-06-04.
  27. Red Hat. 2019. "Ansible Quick Start Video." Accessed 2019-06-03.
  28. Sesto, Vince. 2019. "2019 — Ansible Takes Over As Top Cloud Configuration Management Tool." SplunkUDA, via Medium, March 07. Accessed 2019-06-06.
  29. Thomas, Nyambati. 2017. "Getting started with Ansible." Scotch, May 10. Accessed 2019-06-04.

Further Reading

  1. Ansible Docs. 2019a. "Glossary." Ansible 2.8, May 28. Accessed 2019-06-04.
  2. Thomas, Nyambati. 2017. "Getting started with Ansible." Scotch, May 10. Accessed 2019-06-04.
  3. DeHaan, Michael. 2013. "The Origins of Ansible." Blog, Ansible, December 08. Accessed 2019-06-04.
  4. Shi Ching, Tien. 2018. "Ansible Basics in 5 Minutes." Faun, via Medium, August 04. Accessed 2019-06-04.
  5. Chauveau, Florent. 2018. "CI/CD: Using GitLab + Docker + Ansible." Blog, Callr, September 20. Accessed 2019-06-03.

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Cite As

Devopedia. 2022. "Ansible." Version 4, February 15. Accessed 2023-11-13. https://devopedia.org/ansible
Contributed by
3 authors

Last updated on
2022-02-15 11:53:36
tools system devops automation

See Also