What is blue/green deployment?

The main purpose of the blue/green deployment pattern is to reduce downtime and deployment risk by maintaining two identical production environments: blue for the current version and green for the new release.

When the update is fully tested in the green environment, traffic is seamlessly switched from blue to green. This approach allows new features and fixes to be deployed with minimal disruption, while also making it easy to roll back to the previous version if issues arise.

Both are deployment strategies designed to release new software versions with minimal risk, but they take different approaches.

Blue/green deployment relies on two complete environments. The old version (blue) keeps serving traffic while the new version (green) is being prepared. Once tested, all users are switched at once. It’s fast and reduces downtime, but rollback is also "all or nothing."

Canary deployment takes a more gradual path. The new version is released to a small portion of users first, monitored for errors or performance issues, and then rolled out step by step to everyone. This lowers risk and provides early feedback before full release.

The blue/green deployment process follows a series of steps designed to ensure smooth releases and quick rollbacks if needed:

1. Prepare the new release – Develop and test the new application version in a staging environment.
2. Deploy to the green environment – Deploy the release to the green environment, which mirrors the current blue environment but is not yet live.
3. Test – Validate the new version in the green environment to confirm that it works as expected without impacting users.
4. Switch traffic – Redirect production traffic from blue to green, typically through a load balancer or DNS update.
5. Monitor – Observe the green environment after it goes live to detect and resolve issues quickly.
6. Fallback if needed – In case of problems, immediately redirect traffic back to blue to minimize disruption.
7. Cleanup – Once green is stable, decide whether to update blue with the same changes, keep it as a backup for the next cycle, or shut it down to save costs.

Implementing a blue/green deployment requires careful planning and strong automation. The goal is to keep both environments consistent, control traffic safely, and ensure that rollbacks are fast if problems occur. Here’s a step-by-step approach:

STEP 1. Get the foundations right

• Match environments: blue and green must be identical in runtime, config, and dependencies.
• Manage config and secrets centrally (for example, parameter store, vault).
• Define everything with IaC so you can recreate either environment consistently.

STEP 2. Prepare CI/CD

• Build once and promote the same artifact to green.
• Run automated unit, integration, and smoke tests on every build.
• Gate production promotion with approvals and quality checks.

STEP 3. Handle data safely

• Use backward-compatible schema changes (expand, migrate, contract).
• Keep dual-write or read-compatibility if needed during the switch.
• Run migrations on green ahead of time; verify data access before cutover.

STEP 4. Stand up the green environment

• Provision infrastructure that mirrors blue.
• Deploy the new version to green.
• Run smoke tests, synthetic checks, and load tests against green endpoints.

STEP 5. Put traffic under your control

• Use a controllable entry point: load balancer, API gateway, DNS, or service mesh.
• Prefer connection-draining and health checks to avoid dropping live sessions.
• Support weighted routing so you can shift gradually if desired.

STEP 6. Switch traffic

• Start with a small percentage to validate real traffic, then ramp to 100% if healthy.
• Confirm KPIs: latency, error rates, saturation, business metrics.
• Keep blue warm until you are confident the release is stable.

STEP 7. Monitor and roll back fast

• Monitor logs, metrics, and traces for both environments.
• If issues appear, redirect traffic back to blue immediately.
• Capture diagnostics from green to fix forward.

STEP 8. Clean up and prepare the next cycle

• Either update blue to the new version to become the next "standby," or deprovision it to save cost.
• Archive artifacts, test reports, and deployment metadata.