Which tools are the best-known configuration-automation tools, and what do they have in common?

Ansible, Puppet and Chef. All three are relatively easy to learn, exist as open-source versions, and use plugins and adapters to control many kinds of resources.

These three dominate classic configuration management, the job of putting and keeping servers in a defined configuration. Their shared traits explain why they spread so widely:

• Relatively easy to learn: you describe configuration in a readable language instead of writing shell scripts from scratch.
• Open-source versions exist: teams can start for free and buy commercial support later.
• Plugins and adapters: the core stays small, and extensions let it control operating systems, cloud APIs, databases and network devices, directly or indirectly.

Puppet was the first of the modern tools: released as open source in 2005, then commercialised by Puppet Labs as Puppet Enterprise in 2011. Chef followed in 2009 and Ansible in 2012.

Go deeper:

• Comparison of open-source configuration management software (Wikipedia) — side-by-side tables of Ansible, Puppet, Chef, Salt and others: language, agent, push/pull, platforms.
• Puppet (software) (Wikipedia) — history from the 2005 open-source release, and its agent-based pull model.
• Progress Chef (Wikipedia) — the 2009 Ruby-based tool and its recipe/cookbook model.