Strangler Fig Migration Pattern
- The Strangler Fig pattern gradually replaces a legacy system with a new one by migrating modules from the legacy system to the new system while maintaining correct traffic routing.
- Carta used this pattern to successfully update their HR systems integration, enabling the launch of their new compensation product.
Migration Process
- The migration process involved decomposing a monolithic HR system into smaller, event-driven services.
- A new service with no functionality was created to ensure no disruption to existing functionality.
- A facade layer was created to route traffic to the new service with minimal code changes.
- Customers were migrated from the old service to the new service, starting with the HR provider with the fewest customers to minimize risk.
- Custom tooling was developed to manage the migration.
Challenges and Considerations
- Challenges included data compatibility, stakeholder management, and unexpected business requirements.
- Trade-offs and technical debt were used to mitigate risks and meet business needs.
- The migration took several years and is still ongoing, but the new system now handles most of the traffic.
- Understanding risk profiles and making conscious decisions about technical debt are crucial during complex migrations.
Benefits and Learnings
- The migration improved customer experience by ensuring uninterrupted workflows.
- Instrumenting the migration process with monitoring tools allowed for quick issue detection and resolution.
- Visibility into the health of customer integrations was improved.
- Considering future maintainability and modularity is essential when implementing changes.
- The incremental nature of the Strangler Fig approach allowed migration progress to continue despite organizational changes.
- The migration took longer than initially estimated, but the cautious and incremental approach was valuable.
Applicability and Limitations
- The Strangler Fig pattern may not be suitable for all scenarios, such as simple implementations or tightly coupled systems.
- The team is currently using the pattern not only for decomposition but also for recomposing certain components back into the monolith.
- Potential pushback, such as the perception of migration tools as "throwaway work," can be addressed by emphasizing customer satisfaction benefits.
Advantages of Strangler Fig
- Provides psychological safety to engineers by allowing quick issue identification and remediation.
- Leads to better code, faster progress, and more innovation.
- Introduces minimal overhead with sufficient observability and understanding of workflow impact.
Convincing Leadership
- Customer-focused arguments, such as faster data syncs, easier integration of new providers, and improved performance, are effective in gaining leadership support.
Importance of Observability
- Observability tools provide visibility into the system and ensure a smooth migration process.
