adaptive-enforcement-lab/strangler-fig

Strangler Fig

When to Use This Skill

Use when:

• Replacing critical production systems
• High risk of downtime
• Need gradual validation
• Rollback must be instant

Don't use when:

• Small, non-critical systems (just replace)
• No production traffic yet
• Resource cost of running both systems is prohibitive

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Implementation

Traffic Routing Approach

• Implementation Strategies - Feature flags, parallel run validation, database migration strategies
• Traffic Routing - Percentage-based, user-based, and canary deployment patterns
• Monitoring and Rollback - Track both systems, compare metrics, instant rollback

Component Replacement Approach

• Platform Component Replacement - Build-replace-remove pattern for infrastructure, zero downtime component swaps

Migration Process

• Migration Guide - Eight-phase checklist, common pitfalls, real-world timeline

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Techniques

Two Approaches to Strangler Fig

The strangler fig pattern has two distinct implementation approaches depending on what you're replacing:

Approach 1: Traffic Routing (User-Facing Systems)

Gradually shift user traffic from old to new system using percentage-based routing.

Use for:

• API migrations (REST v1 → v2)
• Feature rollouts (old checkout → new checkout)
• UI rewrites (legacy frontend → modern frontend)
• Application logic changes

How it works: Router/proxy directs percentage of traffic to new system. Start at 1%, increase gradually to 100%.

Approach 2: Component Replacement (Infrastructure)

Replace entire components without routing traffic, including databases, service meshes, operators, and storage.

Use for:

• Database migrations (single instance → HA cluster)
• Service mesh replacement (Linkerd → Istio)
• Operator upgrades (CRD v1alpha1 → v1)
• Storage backend changes (EBS → EFS)

How it works: Build new component, ensure compatibility, swap references, remove old component. No routing layer needed.

Key distinction: Traffic routing = gradual user migration. Component replacement = infrastructure swap with compatibility layer.

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Examples

See examples.md for code examples.

Related Patterns

• Separation of Concerns
• Graceful Degradation
• Environment Progression

References

• Source Documentation
• AEL Patterns