Blue-green deployment vs Progressive delivery: Choosing a deployment strategy

Blue-green deployment

Blue-green deployment is a release strategy that minimizes downtime by maintaining two identical environments: one running the current production version (blue) and another for the new release (green). After deploying to the green environment and verifying its functionality through testing, traffic is switched from blue to green, typically through a simple DNS change or load balancer configuration update. This approach offers a quick rollback mechanism if issues are detected after the switch.

The primary advantage of blue-green deployment is risk reduction through complete environment separation. Since the entire platform moves from one version to another simultaneously, there’s consistency across the system. However, this approach requires double the infrastructure resources and doesn’t allow for gradual user migration or targeted testing with specific user segments.

Progressive delivery

Progressive delivery extends continuous delivery by gradually rolling out changes to users while monitoring system health. Instead of switching all traffic at once, this approach implements controlled exposure through techniques like canary releases, percentage-based rollouts, or targeted cohorts. With each increment, teams analyze metrics and feedback before expanding the release to more users.

This method reduces risk by limiting the impact of potential issues to a small subset of users while gathering real-world performance data. Progressive delivery enables teams to validate changes in production with actual user traffic, allowing for data-driven decisions about whether to proceed with the full deployment, make adjustments, or roll back with minimal disruption. It requires more sophisticated monitoring and deployment infrastructure but offers greater control over the release process.

Comparison: Blue-green deployment vs. progressive delivery

Risk management

• Blue-Green: All-or-nothing approach with immediate full rollback capability.

• Progressive: Incremental risk with limited blast radius during initial stages.

Infrastructure requirements

• Blue-Green: Requires duplicate production environments, increasing resource costs.

• Progressive: Can operate with additional partial capacity rather than full duplication.

Deployment speed

• Blue-Green: Typically faster total deployment time as the switch happens all at once.

• Progressive: Longer overall deployment timeline as the rollout proceeds through stages.

Feedback loops

• Blue-Green: Limited pre-release validation with real users unless specifically arranged.

• Progressive: Built-in real-user validation during the deployment process itself.

Complexity

• Blue-Green: Conceptually simpler with fewer moving parts to manage.

• Progressive: More complex orchestration requiring advanced tooling and monitoring.

User experience

• Blue-Green: All users experience the change simultaneously.

• Progressive: Different users may experience different versions during the rollout period.

Feature flags with deployment strategies

When used with blue-green deployments, feature flags add an additional layer of control. While the blue-green approach handles the infrastructure transition, feature flags manage the functional aspects of the release. Teams can deploy the new green environment with features turned off, verify the technical deployment, then gradually enable features after the traffic switch occurs. This hybrid approach maintains the clean separation of environments from blue-green deployment while allowing more granular control over feature exposure. If a specific feature causes issues, it can be toggled off without rolling back the entire environment switch.

Progressive delivery naturally complements feature flags, creating a powerful combination for controlled releases. In this scenario, feature flags become the primary mechanism for implementing the progressive aspect, allowing teams to define sophisticated rollout rules based on user segments, geography, or other criteria. As the deployment progresses through its stages, different flags can be enabled for different user populations while maintaining constant monitoring. This pairing gives teams maximum flexibility to accelerate or pause specific feature rollouts independently of the underlying deployment, creating a fine-grained approach to managing both technical and business risks.

Blue-green deployment offers a reliable approach to updating applications by maintaining two identical environments: one running the current version (blue) and another for the new release (green). Once the green environment is validated, traffic switches over completely, providing instant rollbacks if issues arise. This method excels in scenarios requiring zero downtime and when applications need complete version switching rather than partial updates. However, it demands significant infrastructure resources to maintain duplicate environments and forces an all-at-once transition that can make issue isolation challenging.

Progressive delivery, in contrast, gradually exposes users to new functionality through techniques like canary releases, feature flags, and A/B testing. This approach reduces risk by limiting potential issues to a subset of users and allows for real-world testing with actual traffic patterns. Progressive delivery is ideal for organizations with robust monitoring capabilities and when collecting user feedback on new features is crucial. Choose progressive delivery when you need fine-grained control over feature rollouts and have the technical capability to segment users. Opt for blue-green deployment when your application requires complete, atomic updates or when your infrastructure can support duplicate environments without incurring excessive costs.

Frequently asked questions

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

Blue-green deployment involves maintaining two identical environments (blue and green), where the blue environment runs the current production version and the green environment hosts the new release. Traffic switches entirely from blue to green after validation. In contrast, canary deployment is a progressive delivery strategy where the new version is gradually rolled out to a small subset of users before expanding to the entire user base. Blue-green is an all-or-nothing approach, while canary allows for incremental exposure and risk management with a limited initial impact.

Can you provide an example of a blue-green deployment?

In a blue-green deployment, you might have your current application version running in the blue environment serving all production traffic. You deploy the new version to the green environment and perform testing to verify its functionality. Once validated, you update your load balancer or DNS configuration to route all traffic from the blue to the green environment. If issues are detected after the switch, you can quickly revert traffic back to the blue environment, providing a simple rollback mechanism with minimal downtime.

How is blue-green deployment implemented on AWS?

On AWS, blue-green deployment can be implemented using several services. You can use Elastic Load Balancing to route traffic between environments by updating target groups. AWS CodeDeploy supports blue-green deployments natively, allowing you to shift traffic gradually or all at once between environment versions. For containerized applications, Amazon ECS and EKS support blue-green deployments through task definitions or Kubernetes deployments. Route 53 can be used for DNS-based traffic routing between environments. These services enable automated environment creation, testing, and traffic shifting with minimal manual intervention.

What is canary deployment and how does it work?

Canary deployment is a progressive delivery strategy where a new application version is gradually rolled out to users. Initially, the new version is deployed to a small subset of users or servers (the “canary”), typically 5-10% of traffic. This limited exposure allows teams to monitor the performance, error rates, and user feedback of the new version with real production traffic while minimizing potential impact. If metrics remain healthy, the deployment continues incrementally to larger user segments until reaching 100%. If issues are detected, the rollout can be paused or rolled back, affecting only the small percentage of users exposed to the canary.

What strategies are involved in blue-green deployment?

Blue-green deployment involves several key strategies: environment duplication to maintain identical blue and green infrastructures; validation testing in the green environment before any traffic switch; traffic routing mechanisms through load balancers or DNS to redirect users between environments; database compatibility planning to ensure both versions can work with the data layer; and rollback procedures for quick recovery if issues arise after deployment. Some implementations incorporate feature flags as an additional control layer, allowing teams to deploy with features disabled initially, then gradually enable them after the traffic switch has occurred, providing finer-grained control over the release process.