Immutable infrastructure

As explained in Infrastructure as Code, Patterns and Practices: With examples in Python and Terraform

Immutable infrastructure is an infrastructure-management approach in which any configuration change is applied by creating a new resource rather than modifying an existing one.

Immutable infrastructure creates a new resource for every configuration change instead of modifying an existing resource. Replacing resources can reduce failure risk and configuration drift by aligning deployed state with infrastructure as code. section 2.2

Apply the approach through replacement and reconciliation:

• Create a new server with Python 3 and compatible dependencies, then delete the old Python 2 server. section 2.2
• Generate a new machine image for server updates, passing resource-specific values such as IP registration through startup parameters. section 2.2
• If an urgent out-of-band change modifies a resource directly, update version control and infrastructure as code to reconcile actual and desired state. section 2.2.1

Figure 2.2 You treat the server mutably by logging in and updating the Python package version. By comparison, you treat the server immutably by replacing the old server with a new one upgraded to Python 3.

Compare in-place Python updates with replacing the server using an upgraded resource. section 2.2

How Infrastructure as Code, Patterns and Practices: With examples in Python and Terraform covers it

How deep it goes

Defines replacement and explains reconciliation, but stops short of detailed deployment orchestration.

Examples

Uses Python 2-to-3 server replacement, machine image builders, and an out-of-band server update.

What it assumes

Assumes infrastructure as code and version control, while defining immutable and mutable infrastructure explicitly.

What you can do after

Apply it via infrastructure as code by replacing resources and reconciling emergency mutable changes in version control.

How it connects

Connects infrastructure as code with mutable infrastructure, configuration drift, version control, and idempotency.

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Related concepts

• mutable infrastructurecontrasts with · Mutable infrastructure is an infrastructure-management approach in which resources are modified in place without being recreated or restarted.
• machine imageuses · A machine image is a packaged template containing an operating system, software, and configuration used to create or launch computing instances.
• cloud-native architectureused by · Cloud-native architecture is an approach to designing and operating applications to exploit cloud infrastructure and services, including distributed operation, elasticity, and automated management.
• load balanceruses · A load balancer is a hardware or software component that distributes incoming network traffic or requests among multiple destinations, such as servers or service instances.
• driftaddresses · Drift is a change over time in a system’s behavior, state, data, or configuration relative to a reference or expected baseline.

This explainer was generated by Manning's knowledge graph from the text of Infrastructure as Code, Patterns and Practices: With examples in Python and Terraform. The section links point to the parts of the book it draws on.