Canary release vs smoke test: Choosing a deployment strategy

Canary release

Canary release is a deployment strategy where new software versions are gradually rolled out to a small subset of users or servers before being deployed to the entire production environment. This approach allows teams to monitor the new version’s performance, stability, and user experience with real production traffic while minimizing the blast radius of potential issues. The name comes from the historical practice of using canary birds in coal mines to detect dangerous gases.

The canary deployment typically starts with routing a small percentage of traffic (often 1-5%) to the new version while the majority continues using the stable version. If the canary performs well based on predefined metrics and monitoring, the rollout gradually increases until 100% of users are on the new version. If issues arise, traffic can be quickly redirected back to the stable version, limiting the impact to only the small group of canary users.

Smoke test

Smoke testing is a deployment strategy that involves running a basic set of tests immediately after deployment to verify that the most critical functions of the application are working correctly. These tests are designed to be quick, lightweight, and focused on core functionality rather than comprehensive testing. The term originates from electronics testing, where powering on a device and checking if it produces smoke was a basic way to determine if it was fundamentally broken.

Smoke tests typically cover essential features like application startup, database connectivity, API endpoints, and basic user workflows to ensure the deployment hasn’t introduced any show-stopping issues. These tests serve as a safety net to catch major problems early in the deployment process, allowing teams to quickly rollback if critical functionality is broken. While not exhaustive, smoke tests provide confidence that the basic system is operational before users begin interacting with the new deployment.

Comparison: Canary release vs Smoke test

Scope

• Canary release: Focuses on gradual user exposure and real-world performance monitoring

• Smoke test: Focuses on immediate technical validation of core system functionality

Timing

• Canary release: Extends over hours, days, or weeks as traffic gradually increases

• Smoke test: Completes within minutes immediately after deployment

Risk mitigation

• Canary release: Limits user impact by exposing only a small percentage to potential issues

• Smoke test: Prevents widespread issues by catching critical failures before general availability

Feedback mechanism

• Canary release: Uses real user behavior, performance metrics, and business KPIs

• Smoke test: Uses automated test results and system health checks

Rollback trigger

• Canary release: Triggered by degraded metrics, user complaints, or performance issues over time

• Smoke test: Triggered by immediate test failures or system unavailability

Feature flags with Canary release

Feature flags work synergistically with canary releases by providing fine-grained control over which users see new features and when. Rather than deploying entirely new versions to canary users, feature flags allow teams to selectively enable specific features for the canary group while keeping the same codebase across all users. This approach enables more targeted testing and reduces the complexity of managing multiple deployment versions.

The combination of feature flags and canary releases also provides enhanced rollback capabilities and more sophisticated user targeting. Teams can instantly disable problematic features for canary users without requiring a full deployment rollback, and they can target canary groups based on user attributes, geographic location, or device type. This creates a more controlled and flexible deployment environment where features can be tested independently and rolled back granularly.

Feature flags with smoke tests

Feature flags complement smoke testing by allowing teams to deploy code with new features in a disabled state, then enable them only after smoke tests pass successfully. This approach ensures that smoke tests validate the system’s stability before any new functionality becomes available to users. The feature flags can be automatically toggled on as part of the deployment pipeline once all smoke tests complete successfully.

Additionally, feature flags provide a safety mechanism during smoke testing by allowing teams to quickly disable specific features if they cause smoke test failures without requiring a full rollback. This enables more granular problem isolation and faster resolution times, as teams can identify which specific features are causing issues and disable only those components while keeping the rest of the deployment intact. The combination creates a more resilient deployment process where technical validation and feature activation are decoupled.

Canary releases offer the significant advantage of gradual risk mitigation by exposing new features to only a small subset of real users in production, allowing teams to monitor real-world performance and user behavior before full deployment. This approach provides authentic feedback from actual usage patterns and enables quick rollback if issues arise, minimizing the blast radius of potential problems. However, canary releases require sophisticated infrastructure for traffic splitting and monitoring, can be complex to implement properly, and may create inconsistent user experiences when different users see different versions of the application. The approach also demands robust monitoring and alerting systems to detect issues quickly, and may not catch all problems if the canary group is too small or not representative of the broader user base.

Smoke testing, on the other hand, provides fast and automated validation of critical system functionality immediately after deployment, ensuring that basic features work correctly before any real users interact with the system. This approach is relatively simple to implement, doesn’t require complex infrastructure, and can quickly catch obvious deployment issues or environmental problems. However, smoke tests are limited in scope and only verify basic functionality rather than comprehensive system behavior, may not catch performance issues under real load, and cannot detect problems that only emerge with actual user interactions or edge cases. Choose canary releases when you need to validate complex features with real user feedback, have the infrastructure to support gradual rollouts, and want to minimize risk for critical production systems. Opt for smoke testing when you need quick validation of basic functionality, are working with simpler deployment scenarios, or want to catch obvious issues immediately after deployment before proceeding with further testing or release strategies.