2.1.4.3. Mutable vs. Immutable Deployment Patterns

First Principle: Immutable deployments fundamentally enhance consistency, reliability, and simplify rollbacks by ensuring that no changes are made to deployed components after initial provisioning.

Understanding mutable versus immutable deployment patterns is fundamental to modern DevOps practices. This distinction impacts consistency, reliability, and rollback capabilities.

Mutable Deployments:

• Concept: Updates are applied directly to existing servers or instances.
• Process: New code is deployed, or configurations are changed on running instances.
• Pros: Simple to implement for small changes.
• Cons: Leads to configuration drift ("snowflake servers"), difficult to reproduce issues, complex rollbacks, higher risk of downtime.

Immutable Deployments:

• Concept: A new, fully configured environment (e.g., new EC2 instances from a new AMI, new container images) is created for each deployment.
• Process: The old environment is replaced by the new one.
• Pros: Eliminates configuration drift, simplifies testing, ensures consistency, enables fast and reliable rollbacks (by simply reverting to the old environment).
• Cons: Requires more upfront automation for image/environment creation.

AWS Services supporting Immutability: EC2 Image Builder (for AMIs), AWS CodeDeploy (for Blue/Green deployments), container services (ECS, EKS) inherently support immutability.

Key Differences: Mutable vs. Immutable Deployments:

• Mutable: In-place updates, configuration drift, complex rollback, higher risk.
• Immutable: New environment, no drift, simple rollback, lower risk.

Scenario: A DevOps team is dealing with frequent "it worked in staging, but not in production" issues due to environmental inconsistencies caused by in-place updates. They want to adopt a deployment pattern that guarantees environment consistency and simplifies rollbacks.

Reflection Question: How would adopting an immutable deployment pattern (e.g., using EC2 Image Builder for AMIs) fundamentally solve the problem of configuration drift and simplify rollbacks compared to mutable deployments?

Immutable deployments are a cornerstone of reliable, scalable, and resilient systems in the cloud.

💡 Tip: Embrace immutable infrastructure. While it requires more automation initially, the long-term benefits in terms of reliability, consistency, and simplified operations are significant.