Blue-green deployment vs smoke test: Choosing a deployment strategy

Blue-green deployment

Blue-green deployment is a strategy that reduces downtime and risk by running two identical production environments called blue and green. At any given time, only one environment is live, serving all production traffic. When a new version of the application is ready for release, it is deployed to the non-live environment. After testing the new version in the non-live environment, traffic is switched from the live environment to the newly deployed environment. This switch is typically accomplished through a router or load balancer update.

The primary advantage of blue-green deployment is the ability to quickly roll back to the previous version if issues are detected in the new release. Since the previous environment remains intact until the new deployment is confirmed successful, switching back involves simply redirecting traffic to the original environment. This approach minimizes downtime and provides a safety net for deployments, though it does require maintaining duplicate infrastructure.

Smoke testing

Smoke testing is a deployment strategy that involves running a subset of tests after deploying a new version to ensure the most critical functionality works correctly. These tests are designed to be quick and focused on core features, acting as an early warning system to catch significant issues before they affect users. If smoke tests fail, the deployment can be automatically rolled back, preventing widespread impact.

This approach is particularly valuable for rapid verification in continuous delivery pipelines. Smoke tests typically check basic functions like application startup, login capabilities, and critical user journeys. Unlike comprehensive testing, smoke tests don’t aim to verify every feature but instead confirm that the application is stable enough for further testing or user interaction, making them an efficient first line of defense in deployment validation.

Comparison: Blue-green deployment vs. smoke testing

Risk mitigation

• Blue-Green: Provides immediate rollback capability by maintaining two complete environments, reducing risk of extended downtime.

• Smoke Testing: Identifies critical issues quickly before full user exposure, allowing for early intervention.

Resource requirements

• Blue-Green: Requires duplicate infrastructure, increasing resource costs and maintenance overhead.

• Smoke Testing: Needs minimal additional resources beyond the test scripts themselves, making it cost-effective.

Implementation complexity

• Blue-Green: Involves more complex routing and infrastructure management to maintain parallel environments.

• Smoke Testing: Relatively simple to implement as it focuses on creating targeted test scripts for critical paths.

Deployment speed

• Blue-Green: Can potentially slow deployment due to the need to provision and validate a complete second environment.

• Smoke Testing: Accelerates the deployment pipeline with quick verification, allowing faster delivery cycles.

User impact

• Blue-Green: Users typically experience zero downtime as traffic is redirected seamlessly between environments.

• Smoke Testing: May expose users to bugs in non-critical functionality that smoke tests don’t cover.

Feature flags with deployment strategies

When using feature flags with blue-green deployments, teams can deploy new code to the green environment with features turned off, then validate the deployment’s technical aspects without exposing new functionality. Once the green environment is live and receiving traffic, features can be gradually enabled for specific user segments through the feature flag system. This approach adds an additional safety layer to blue-green deployments, allowing teams to separate the technical deployment from the feature release and enabling a controlled rollout even after the environment switch has occurred.

In smoke testing scenarios, feature flags serve as a complementary risk mitigation strategy. Teams can deploy code with new features hidden behind flags, then run smoke tests on the core application functionality. After passing these initial tests, teams can enable features for internal testers or a small percentage of users while monitoring for issues. This progressive exposure model works particularly well with smoke testing’s quick validation approach, as it allows teams to detect both critical application issues and feature-specific problems in a controlled manner, significantly reducing the blast radius of potential bugs.

Blue-green deployment and smoke testing are both strategies aimed at minimizing risks in software releases, but they serve different purposes and have distinct advantages. Blue-green deployment involves maintaining two identical production environments (blue and green), with only one active at a time. This strategy allows for seamless releases by routing traffic from the old version (blue) to the new version (green) after it’s fully deployed and tested. The primary benefits include zero downtime during deployment, straightforward rollback capabilities by simply reverting traffic to the previous environment, and the ability to thoroughly test the new version in isolation before exposing it to users. However, blue-green deployments require twice the infrastructure resources, which increases costs, and they can be complex to implement, especially with database schema changes or when maintaining state across environments.

Smoke testing, on the other hand, is a preliminary testing technique where a subset of the application’s critical functionalities is verified after deployment to ensure basic operation. This approach is less resource-intensive than blue-green deployment as it doesn’t require duplicate infrastructure. Smoke tests are quick to execute and can rapidly identify major issues before they affect all users. Choose blue-green deployment when downtime is unacceptable, when the application serves critical business functions, or when you need the security of an instant rollback option. Opt for smoke testing when resources are limited, when you’re deploying smaller, less risky changes, or as part of a larger testing strategy. Many organizations actually implement both: using smoke tests within a blue-green deployment process to verify the new environment before switching traffic, combining the strengths of both approaches for optimal release safety.

Frequently asked questions

What is the difference between blue-green deployment and canary deployment?

Blue-green deployment involves maintaining two identical production environments (blue and green) with only one active at a time. When a new version is ready, it’s deployed to the inactive environment, tested, and then all traffic is switched over at once. Canary deployment, on the other hand, gradually routes a small percentage of traffic to the new version while monitoring for issues, then slowly increases the traffic until the new version handles all requests. Blue-green offers immediate rollback capability but requires duplicate infrastructure, while canary provides more gradual risk exposure with potentially less infrastructure overhead.

Can you provide an example of blue-green deployment?

A typical blue-green deployment might work like this: Company X has a web application currently running version 1.0 in the “blue” environment serving all production traffic. When version 2.0 is ready, it’s deployed to the “green” environment. The team runs tests on the green environment to ensure everything works correctly while users continue to use version 1.0 in the blue environment. Once testing confirms the green environment is stable, the team updates their load balancer configuration to route all traffic to the green environment. Users are now seamlessly using version 2.0. If any issues are discovered, traffic can be immediately routed back to the blue environment, restoring version 1.0 with minimal downtime.

How is blue-green deployment implemented on AWS?

On AWS, blue-green deployment can be implemented using several services. A common approach is to use AWS Elastic Load Balancing (ELB) to direct traffic between two separate sets of EC2 instances or ECS tasks. AWS CodeDeploy provides built-in support for blue-green deployments, allowing you to specify how traffic should be shifted. For containerized applications, Amazon ECS and EKS support blue-green deployments through task definitions or Kubernetes deployments. Route 53 can also be used for DNS-based switching between environments. The process typically involves creating a new set of resources for the green environment, deploying the new application version, validating it works correctly, and then updating the routing configuration to direct traffic to the new environment.