Blue-Green vs Canary Deployment: A Comprehensive Comparison

In this blog post a high-level comparison is provided between blue-green deployments versus those known as canary deployments.

Blue-Green Deployment

Overview: This strategy involves maintaining two identical environments: a live “blue” environment and a new “green” environment. Once the green environment is validated, traffic is quickly switched from blue to green. How the switch is done quickly can vary. This could be a symlink change at a file system level, instance member change at an ELB level and many more.

Benefits:

• Fast Rollout: Quick transition between environments.
• Easy Rollback: If issues arise, traffic can be switched back to the blue environment.
• Minimal Downtime: Ideal for critical applications requiring continuous operation.

Drawbacks:

• Resource Intensive: Requires maintaining two environments, which can be costly. In highly regulated environments it may increase not just budget needs for two individual environments but also the operational needs to be able to meet compliance requirements.

Canary Deployment

Overview: This approach involves gradually rolling out updates to a small subset of users before deploying to the entire user base. To be able to present updates to a small subset of users an option is to utilize AWS Route53’s balanced weight pools. A deep-dive on R53’s balanced weight pools and other features is talked about in a different blog post in this blog.

Benefits:

• Risk Management: Allows for real-world testing with minimal risk.
• Resource Efficiency: Only requires a small staging environment. Depends on the design the staging environment can be eliminated after a full switch is completed.
• Gradual Rollout: Enables monitoring and feedback from users before full deployment.

Drawbacks:

• Time-Consuming: Requires careful monitoring and gradual traffic redirection.

Choosing Between Blue-Green and Canary Deployments

• Blue-Green: Ideal for applications with low risk tolerance and sufficient resources. If an issue (such as a bug) is not discovered during testing/QA it gets exposed to the entire user base after environment switched.
• Canary: Suitable for projects with limited resources or those requiring iterative risk management. The programmatic efforts are potentially larger compared to blue-green deployments. However, the granularity and ability to present a small portion of updates/next release to – therefore – a small subset of users might be worth the efforts.

Both strategies offer no-downtime upgrades and easy rollbacks. Overall there is no right or wrong between both deployment methodologies. Rather a business or use case would describe the requirements needed leading the option which meets the requirements at best.