Container images package code and runtime dependencies but should not contain production secrets.

How to apply it

Use supported base images, deterministic dependency installation, non-root execution, small build context, and scans. Separate readiness from liveness; gracefully stop traffic and handle in-flight work during shutdown.

Worked example

Readiness verifies serving capability; liveness detects a stuck process without depending on every external provider.

Common mistakes to avoid

Restart storms during provider outages or copying secrets into images.

Practice task

Implement this concept in the capstone. Add one positive test, one negative or failure-path test, and a short note explaining the trade-off you chose.