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In modern cloud-native environments, managing infrastructure reliably and predictably is critical. This article examines the key differences between immutable and non-immutable (mutable) infrastructures, highlights their respective workflows, and demonstrates why immutable approaches are often the preferred choice for large‐scale deployments.

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Immutable Infrastructure

Immutable infrastructure treats every change as a brand-new deployment. Once you build an image, you never modify it in place—instead, you replace the entire environment with a fresh image.
The image illustrates the concept of an immutable environment, showing a process where a base AMI is combined with changes to create a package, which is then used to replace existing environments.
How it works:
  1. Base Image
    Start from a golden AMI or container image template.
  2. Build Pipeline
    Apply OS patches, configuration, and application code to produce a new image version.
  3. Deploy New Instances
    Launch servers or containers from the freshly built image.
  4. Decommission Old Version
    Once health checks pass, terminate legacy instances.
Key benefits:
  • Consistency: Every deployment uses the same vetted image.
  • Reliability: Zero configuration drift—environments remain identical.
  • Fast Rollback: Switch back to a previous image version with minimal effort.
Immutable deployments integrate seamlessly with CI/CD pipelines and Infrastructure as Code (IaC) tools. Check out Infrastructure as Code (IaC) for more.

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Non-Immutable (Mutable) Infrastructure

Mutable infrastructure updates running servers or containers in place. Over time, manual patches or ad‐hoc scripts can introduce inconsistencies across your fleet.
The image illustrates a process in a non-immutable environment, showing steps from requiring change, applying changes, to repackaging. It uses icons of boxes and food items to represent these stages.
Typical workflow:
  1. Change Request
    Identify a bug, patch, or configuration update.
  2. In-Place Update
    SSH into servers or run configuration management tools (Ansible, Chef).
  3. Optional Repackage
    Snapshot or bake a new image if desired.
  4. Continue Patching
    Repeat for each environment.
Common drawbacks:
  • Configuration drift leads to unpredictable behavior.
  • In-place updates can cause unplanned downtime.
  • Difficult to reproduce the exact state of an environment.
Untracked changes increase security risk. Regular audits are essential when using mutable infrastructure.

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Immutable vs Mutable: At a Glance

FeatureImmutable InfrastructureMutable Infrastructure
Change MethodDeploy new imageUpdate in place
Configuration DriftVirtually zeroHigh risk
RollbackSimple image version swapTime‐consuming manual remediation
Automation CompatibilityNative IaC & CI/CD integrationLimited; requires extra scripting
DowntimeMinimal (blue/green, canary)Possible during patching

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ACME Corporation’s Immutable Deployment Pipeline

ACME Corporation standardized on an immutable approach to guarantee consistency across development, staging, and production.
The image depicts a flowchart for Acme Corporation's immutable environment, showing an image build process leading to different AMI versions with associated technologies like Nginx, Node.js, and Go.
  1. Automated Image Build
    A CI/CD job generates an EC2 AMI including base OS patches plus required services (Nginx, Node.js, Go).
  2. Development Testing
    Deploy the new AMI in a dev environment for unit and integration tests.
  3. Staging Validation
    Promote the same AMI to staging to ensure parity with production.
  4. Production Release
    Roll out the identical AMI to production servers—no in-place changes allowed.
When a hotfix is needed, ACME simply creates a new AMI revision and reruns the pipeline. This approach eliminates patch drift and keeps all environments predictable.

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Additional Resources

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