Blue-green deployment vs canary release: Choosing a deployment strategy

Blue-green deployment

Blue-Green deployment is a strategy that maintains two identical production environments, called “Blue” and “Green.” At any time, only one of these environments is live and serving all production traffic. When a new version of software is ready, it is deployed to the inactive environment. After testing and validation, traffic is switched from the active to the previously inactive environment, making the new version live. This switch can be done quickly, often by simply changing a load balancer configuration.

This approach minimizes downtime and risk because the entire platform is deployed and tested before any users are directed to it. If any issues arise after the switch, traffic can be immediately routed back to the previous environment, providing a fast rollback mechanism. Blue-Green deployments are particularly useful for organizations that cannot tolerate downtime but need to regularly update their applications.

Canary release

Canary release is a deployment strategy where a new version of an application is gradually rolled out to a small subset of users before being deployed to the entire user base. Initially, a small percentage of traffic is directed to the new version while most users continue to use the stable version. This allows teams to monitor performance, gather user feedback, and detect any issues in a production environment with minimal impact.

As confidence in the new version increases, the percentage of traffic routed to it can be incrementally increased until all users are on the new version. Named after the historical practice of using canaries in coal mines to detect toxic gases, this approach helps detect problems early with minimal user impact. If problems are found, only a small subset of users is affected, and traffic can be quickly routed back to the stable version.

Comparison: Blue-green vs. canary releases

Risk Exposure:

• Blue-Green: All users are switched simultaneously, exposing the entire user base to potential issues at once.

• Canary: Only a subset of users is initially exposed to changes, limiting the impact of potential issues.

Rollout Speed:

• Blue-Green: Typically faster as the switch happens all at once after validation.

• Canary: Generally slower as it involves gradual, incremental rollout over time.

Infrastructure Requirements:

• Blue-Green: Requires maintaining two complete production environments simultaneously.

• Canary: Can be implemented with a single environment plus additional instances for the canary version.

Feedback Collection:

• Blue-Green: Limited real user feedback before full deployment, relying more on pre-deployment testing.

• Canary: Provides real user feedback from the subset of users on the new version before full rollout.

Rollback Complexity:

• Blue-Green: Simple rollback process by switching traffic back to the previous environment.

• Canary: Rollback involves redirecting the canary traffic back to the stable version.

Cost Considerations:

• Blue-Green: Higher cost due to maintaining two full production environments.
• Canary: Can be more cost-effective as it may not require a complete duplicate environment.

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 releasing a new version, the entire user base is switched simultaneously from one environment to the other. Canary deployment, on the other hand, gradually rolls out changes to a small subset of users first, then incrementally increases traffic to the new version as confidence grows. The key differences include risk exposure (all users at once vs. limited subset), rollout speed (faster vs. slower), and feedback collection (limited pre-deployment testing vs. real user feedback before full rollout).

Can you provide an example of blue-green deployment?

In a blue-green deployment scenario, imagine you have two identical production environments. The blue environment is currently serving all your users with version 1.0 of your application. When version 2.0 is ready, you deploy it to the green environment while the blue environment continues handling all traffic. After thorough testing and validation of the green environment, you switch the load balancer configuration to direct all traffic from blue to green. The transition is immediate, with all users now experiencing version 2.0. If any issues arise, you can quickly revert by switching traffic back to the blue environment.

What are the strategies for blue-green deployment?

A key strategy for blue-green deployment involves using feature flags to deploy code in an inactive state to the green environment with features turned off by default. Once the green environment becomes live, features can be gradually enabled without requiring additional deployments. This provides an additional safety layer, as problematic features can be disabled without rolling back the entire deployment. Teams can also use feature flags to perform A/B testing between environments or to enable certain features for specific user segments even after the full traffic switch has occurred.

What is canary deployment and how does it work?

Canary deployment is a strategy where a new version of an application is gradually rolled out to a small subset of users before being deployed to the entire user base. Initially, a small percentage of traffic (e.g., 5%) is directed to the new version while most users continue using the stable version. This allows teams to monitor performance, gather user feedback, and detect any issues in a production environment with minimal impact. As confidence in the new version increases, the percentage of traffic routed to it is incrementally increased until all users are on the new version. If problems are found, only a small subset of users is affected, and traffic can be quickly routed back to the stable version.