Strangler Fig pattern for API versioning

The Strangler Fig pattern is a method for modernizing legacy APIs without disrupting users or causing downtime. Inspired by how a strangler fig plant replaces its host tree, this approach allows old and new systems to coexist, with functionality gradually transitioning to the new system.

Key Points#

• What It Is: A step-by-step approach to replace old APIs by introducing a new system alongside the existing one, using a facade to manage traffic.
• Why Use It: Reduces risk compared to a full rewrite, avoids downtime, and allows incremental updates.
• How It Works:
  • Introduce a facade to route requests between old and new APIs.
  • Migrate functionality in small, manageable pieces.
  • Test and validate each change before retiring legacy components.
• Tools: Platforms like Zuplo assist with routing, monitoring, and managing API migrations efficiently.

This method is particularly useful for transitioning to microservices or updating API versions while maintaining stability and user satisfaction.

Video: Strangler Fig Pattern | Migrate Monolithic Application to Microservices Architecture#

Strangler fig is not a pattern that is limited to API versioning. Check out this video which explains the pattern in the context of microservice migrations to get the full picture:

How the Strangler Fig Pattern Works for API Versioning#

The Strangler Fig pattern allows legacy and new API versions to operate side by side, enabling a smooth and controlled transition without disrupting users.

At its core, this pattern introduces an intermediary layer that sits between API consumers and backend systems. This layer handles routing, ensuring requests are directed to the appropriate API version based on specific rules. Let’s break down how this routing system works during migration.

Using a Facade for Request Routing#

The facade acts as the central routing layer, intercepting all incoming requests and directing them to the correct API version based on predefined rules.

Initially, most requests are routed to the legacy API. As new features are rolled out, the facade gradually shifts targeted requests to the updated components. This ensures API consumers experience no interruptions or compatibility issues during the transition.

The facade’s routing decisions can be based on various factors such as headers, URL paths, client IDs, geographic data, or specific payload characteristics. This flexibility allows teams to roll out new features to select user groups, test performance, and address any issues before a full-scale deployment. If problems arise, the facade can instantly redirect traffic back to the stable legacy version.

Step-by-Step Migration Process#

Migrating with the Strangler Fig pattern involves a structured process that minimizes risks while allowing teams to learn and adapt. Each step builds on the last, creating a clear path from old systems to modernized architecture.

The process starts with clearly identifying system boundaries and dividing the API into smaller, manageable components, often referred to as "thin slices". Once these slices are defined, an intermediary layer is introduced to allow seamless integration of new components without disrupting the existing system.

A great example of this is AltexSoft’s migration of a 20-year-old property management system. The team updated the database structure, added new tables, and deployed new features while ensuring the legacy system remained functional. As new components were tested and validated, they were gradually integrated into the modern architecture.

The migration typically follows a cycle: develop a new component, route traffic to it, monitor its performance, and retire the corresponding legacy component once it’s proven reliable. Over time, the facade evolves, starting with basic passthrough routing and gradually handling more complex traffic patterns as the migration progresses.

The end goal is to fully decommission the legacy system once all functionalities have been successfully transitioned. At this point, teams can either remove the facade entirely or keep it as an adapter layer for legacy clients who haven’t updated their integration methods.

Step-by-Step Guide to Implementing the Strangler Fig Pattern#

Implementing the Strangler Fig pattern requires thoughtful planning and a structured approach. This method ensures a seamless shift from legacy APIs to modern alternatives.

Assessing the Legacy API#

Start by thoroughly analyzing your API's architecture, dependencies, and key functionalities. Map out all endpoints, data flows, and integration points to create a detailed migration plan. Collaborate with experts to uncover hidden business logic and edge cases that might complicate the process. To better understand the current system, develop automated black-box and performance tests that capture its behavior. Adding strategic logging in critical areas - using techniques like aspect-oriented programming - can also provide valuable insights into how the API performs in production.

Break the system into smaller, manageable "thin slices" and prioritize components based on business needs. Begin with a low-risk section of the system to gain confidence before tackling more critical features. Once you’ve mapped out the legacy API, move on to setting up a gateway to manage traffic effectively.

Setting Up a Facade for Traffic Interception#

Deploy an API gateway to serve as the central hub for routing requests. Configure it to direct traffic based on HTTP headers or URL paths. For instance, if you're updating an e-commerce checkout API from version 1 to version 2, you could route requests with a specific header (e.g., x-version=v2) to the new version, while all other requests default to the legacy API. This approach avoids the need for additional proxy layers or overly complex URL structures. Use access logs to verify that routing behaves as expected and to troubleshoot any issues that arise.

Gradual Migration and Testing#

Migrate incrementally, testing at every stage to ensure backward compatibility. For example, provide default values for new endpoint parameters so existing clients remain unaffected. Use unit, integration, and regression tests to catch potential issues early in the process. This steady and deliberate approach allows for a smoother transition. Keep an eye on API adoption rates to determine which versions are actively used, and communicate updates clearly through release notes, migration guides, and updated documentation.

Once the new API versions are stable and meet performance expectations, you can begin deprecating the legacy endpoints.

Removing Legacy APIs#

When the migration is complete and stable, start phasing out legacy APIs. Provide a clear timeline for deprecation and continue supporting older versions during the transition period. Before retiring any legacy endpoints, confirm that they are no longer handling significant traffic. Offer detailed documentation and support to ensure users feel confident throughout the process. For example, a major grocery retailer modernized its coupon management system by first targeting the frequently used but less complex /get_coupons endpoint. This allowed them to validate their approach before moving on to more challenging components.

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Tools and Platforms to Support Migration#

Migrating systems using the Strangler Fig pattern requires tools that can handle intricate routing and monitoring tasks. These tools ensure a smooth transition while minimizing disruptions to users.

Zuplo for Programmable API Management#

Zuplo stands out from traditional API gateways by offering programmable capabilities that allow custom code for advanced routing. Its integration with GitOps ensures that every change - whether it's routing, policy updates, or configuration tweaks - is version-controlled and auditable. This approach minimizes the risk of losing progress or unintentionally rolling back critical rules.

Zuplo is OpenAPI-native, which keeps your gateway aligned with your API specifications throughout the migration. This means as you develop new API versions, the gateway configuration stays consistent with the documented specs, eliminating mismatches between what's deployed and what's described.

The developer portal is another key feature, providing separate, interactive documentation for both legacy and new API versions. This makes it easier for API consumers to identify the correct endpoints during the transition.

Zuplo also offers extensive customization, allowing you to create routing logic tailored to user segments, geographic locations, or specific usage patterns. This flexibility is crucial for managing the complexities of legacy systems.

"Zuplo lets us focus on our API's value, not the infrastructure. Native GitOps and local development works seamlessly. Customizable modules and theming give us complete flexibility. Easy recommendation." - Matt Hodgson, CTO, Vendr

Additionally, Zuplo’s edge deployment processes routing decisions closer to users, reducing latency - a critical factor when balancing traffic between systems with different response times or geographic distributions.

Now, let’s explore how Zuplo supports monitoring and analytics during migration.

Monitoring and Analytics with Zuplo#

Zuplo pairs its routing capabilities with robust monitoring tools to help you maintain stability throughout the migration. Its analytics provide real-time insights into both legacy and new API versions, allowing you to compare performance, track error rates, and observe usage trends.

Custom policies enable advanced migration strategies, such as deploying canary releases to test new versions with specific user groups or automatically rolling back traffic if error rates spike. This ensures a controlled and reliable transition.

The analytics dashboard offers a clear view of traffic distribution across API versions, making it easier to phase out legacy endpoints. By tracking adoption rates of new versions, you can identify and address potential issues before they escalate.

Security and performance are maintained through rate limiting and authentication policies. For example, you can apply stricter rate limits to legacy endpoints while ensuring new versions can handle the expected traffic load.

Benefits and Challenges of the Strangler Fig Pattern#

Building on the migration steps mentioned earlier, let's dive into the key advantages and operational hurdles of using the Strangler Fig pattern.

This pattern offers a practical way to manage API versioning while minimizing risks. One of its standout benefits is risk reduction, as it allows for controlled testing and validation of each change. Additionally, it provides immediate value to users by enabling incremental updates rather than forcing a complete overhaul in one go.

Another major plus is zero downtime. Users can continue accessing familiar endpoints without interruptions, avoiding the confusion and frustration that often come with abrupt system changes.

However, the pattern isn't without its challenges. Running old and new systems in parallel increases resource demands and adds complexity to operations. Essentially, you're maintaining two infrastructures during the transition, which can strain both budgets and team capacity.

Comparison Table: Benefits and Challenges#

While these trade-offs are clear, addressing the operational challenges is crucial to ensure a smooth migration process.

Tackling Common Challenges#

The facade layer is often the most vulnerable point. If it fails, both the old and new systems could become inaccessible. To mitigate this risk, design the facade with redundancy and load balancing to maintain availability and reliability.

Data consistency is another critical issue. When both old and new APIs interact with shared data, synchronization problems can occur. Using event-driven architectures or shared state management strategies can help prevent conflicts and keep systems aligned.

Managing resource usage and operational overhead requires careful planning. As traffic shifts from legacy systems to new ones, you can gradually scale down the resources allocated to older components, keeping costs in check.

Ivan Mosiev highlights another challenge:

"Ongoing analysis is required to assess the impact on legacy systems, which adds complexity as you're dealing with both systems in parallel until the migration is finished".

This parallel operation demands constant monitoring and clear communication across teams to avoid missteps.

Having a rollback strategy for each component is non-negotiable. Feature toggles or dynamic routing make it easier to redirect traffic back to the old system if something goes wrong. This safety net is especially important during high-traffic periods when errors can have a greater impact.

The Strangler Fig pattern is best suited for large, complex systems where its advantages outweigh the added operational demands. For smaller, simpler APIs, alternative versioning methods might be more cost-effective and easier to manage.

Conclusion: API Versioning with the Strangler Fig Pattern#

The Strangler Fig pattern offers a practical way to handle API versioning by gradually phasing out outdated functionalities without disrupting existing operations. As Martin Fowler puts it:

"Rather than replacing a system all at once, it's easier to build a new system around the old, gradually replacing functionalities until the legacy system is phased out."

This method relies on a facade to direct requests between the old and new services, ensuring everything continues to function smoothly during the transition.

To make this process more efficient, having the right tools is critical. For instance, Zuplo supports this approach by enabling separate OpenAPI files for each version, programmable routing through custom policies, and GitOps workflows with unlimited preview environments. These features ensure precise version control and allow for easy rollbacks when needed.

For APIs with complex structures, this pattern aligns with key migration principles. The process hinges on careful planning, ensuring seamless request interception, reliable data synchronization, and ongoing monitoring.

Whether you're moving from monolithic architectures to microservices or updating API contracts, the Strangler Fig pattern allows for steady progress while keeping users happy and systems stable. It provides a structured approach to API modernization that minimizes risk and maximizes efficiency.

FAQs#

How does the Strangler Fig pattern help ensure uninterrupted API migration?#

The Strangler Fig pattern offers a practical way to handle API migration by phasing out old components and introducing new ones gradually. This ensures that users can keep accessing the API without any disruptions during the transition.

The process involves slowly redirecting traffic to the updated components while keeping the legacy system running. This approach reduces risks, preserves system stability, and guarantees a seamless experience for users throughout the migration.

What challenges can arise when using the Strangler Fig pattern for API versioning, and how can they be resolved?#

The Strangler Fig pattern comes with its fair share of challenges. These include maintaining data consistency between the old and new systems, dealing with dependencies across interconnected components, and managing the operational complexity of running both systems simultaneously during the transition.

To tackle these hurdles, you can implement a facade or proxy to efficiently route traffic between the legacy and updated APIs. Careful planning for data migration is crucial to prevent inconsistencies, and taking an incremental approach to updates can help reduce disruptions. This method keeps the system stable while ensuring a smoother experience for users during the transition.

How does Zuplo support the Strangler Fig pattern for API versioning?#

Zuplo makes it easier to use the Strangler Fig pattern by providing a robust API gateway that helps you smoothly transition from legacy APIs to new versions. With Zuplo, you can handle migrations without downtime, centrally manage multiple API versions, and direct traffic intelligently - all while keeping your current users unaffected.

This method lets developers and API managers update systems step by step, ensuring stability and keeping users happy along the way.