MSDN Documentation

Blue-Green Deployment

Blue-Green deployment is a strategy that reduces downtime and risk by running two identical production environments, "Blue" and "Green". At any time, one environment is live (Blue) and the other is idle (Green). To release a new version, you deploy the new version to the idle environment (Green), test it thoroughly, and then switch traffic from the live (Blue) to the new (Green) environment. This allows for instant rollback if issues arise by simply switching traffic back to the Blue environment.

Key Benefits:

• Zero downtime deployments.
• Instant rollback capability.
• Reduced deployment risk.

Considerations:

• Requires duplicated infrastructure, which can increase costs.
• State management for user sessions needs careful handling.

# Example conceptual setup (not actual code)
LOAD_BALANCER_TARGET = BLUE_ENVIRONMENT

# During deployment:
# 1. Deploy new version to GREEN_ENVIRONMENT
# 2. Perform health checks on GREEN_ENVIRONMENT
# 3. Update LOAD_BALANCER_TARGET to GREEN_ENVIRONMENT
# 4. BLUE_ENVIRONMENT becomes idle/rollback target.
                

Canary Release

Canary releases involve gradually rolling out a new version to a small subset of users before making it available to everyone. This "canary" group is monitored closely for errors and performance issues. If the new version proves stable, it's incrementally rolled out to more users until it reaches 100%. This strategy helps detect issues early in a controlled manner, minimizing the impact on the majority of users.

Key Benefits:

• Early detection of bugs and performance regressions.
• Reduced blast radius of potential issues.
• User feedback integration.

Considerations:

• Requires sophisticated traffic routing and monitoring tools.
• Managing different versions of the application concurrently.

# Example conceptual traffic splitting
ROUTING_RULE:
  - condition: user_segment == "canary"
    target: NEW_VERSION_CLUSTER
    weight: 10%
  - condition: all
    target: PRODUCTION_CLUSTER
    weight: 90%
                

Rolling Deployment

In a rolling deployment, new application versions are deployed incrementally by updating instances one by one or in small batches. When an instance is updated, it's taken out of service, updated, and then put back into service. This process continues until all instances are running the new version. It's a common and relatively simple strategy, but can involve brief periods where both old and new versions are running simultaneously, which requires careful consideration for compatibility.

Key Benefits:

• Simple to implement.
• Reduces downtime compared to stop-and-replace deployments.

Considerations:

• Requires careful management of backward and forward compatibility.
• Potential for brief periods of mixed versions.
• No instant rollback.

# Example conceptual update loop
FOR EACH instance IN servers:
  REMOVE instance FROM LOAD_BALANCER
  UPDATE instance WITH NEW_VERSION
  PERFORM HEALTH_CHECK on instance
  ADD instance TO LOAD_BALANCER
                

Feature Flags

Feature flags (or feature toggles) allow you to turn features on or off dynamically without deploying new code. This provides a powerful way to decouple deployment from feature release. You can deploy code containing new features to production, but keep them hidden behind a flag until you're ready to expose them. This can be combined with other deployment strategies like Canary Releases for fine-grained control.

Key Benefits:

• Decouples deployment from release.
• Enables rapid experimentation and A/B testing.
• Quickly disable problematic features.

Considerations:

• Can add complexity to the codebase.
• Requires a robust feature flag management system.