What Is Immutable Infrastructure?

Introduction

In a traditional mutable server infrastructure, servers are continually updated and modified in place. Engineers and administrators working with this kind of infrastructure can SSH into their servers, upgrade or downgrade packages manually, tweak configuration files on a server-by-server basis, and deploy new code directly onto existing servers. In other words, these servers are mutable; they can be changed after they’re created. Infrastructure comprised of mutable servers can itself be called mutable, traditional, or (disparagingly) artisanal.

An immutable infrastructure is another infrastructure paradigm in which servers are never modified after they’re deployed. If something needs to be updated, fixed, or modified in any way, new servers built from a common image with the appropriate changes are provisioned to replace the old ones. After they’re validated, they’re put into use and the old ones are decommissioned.

The benefits of an immutable infrastructure include more consistency and reliability in your infrastructure and a simpler, more predictable deployment process. It mitigates or entirely prevents issues that are common in mutable infrastructures, like configuration drift and snowflake servers. However, using it efficiently often includes comprehensive deployment automation, fast server provisioning in a cloud computing environment, and solutions for handling stateful or ephemeral data like logs.

The rest of this article will:

• Explain the conceptual and practical differences between mutable and immutable infrastructure
• Describe the advantages of using an immutable infrastructure and contextualize the complications
• Give a high-level overview of the implementation details and necessary components for an immutable infrastructure