Unraveling the Strangler Pattern (Part III): Key Strategies for the First Stage of Migration
The Strangler pattern approach enables a gradual transition to modern architectures, free of any disruptive overhauls. However, ensuring business continuity as old and new applications coexist requires strong attention to detail throughout the implementation stage. Careful orchestration is key to achieving a seamless and efficient modernization.
Previously in our series, we detailed the foundations of Strangler pattern and key steps for the planning phase. Now, we jump into action. This blog article will cover essential strategies for effectively starting your Strangler pattern migration.
Setting up a Proxy Layer
The intermediary facade plays a critical role in the Strangler pattern approach, steadily routing user traffic to updated applications while maintaining support for legacy components. If designed improperly, this proxy layer can be a significant bottleneck in your migration.
With that in mind, it’s important to select a suitable reverse proxy technology. Popular options include nginx, HAProxy, and cloud-native solutions such as AWS API Gateway or Azure API Management. Make a selection that aligns well with your existing infrastructure and team expertise. Then, install and configure the proxy server to sit in front of and direct all traffic to your monolithic system.
Here is an example of how your setup should initially look:
As you gradually modernize your applications, you can update the proxy’s routing rules to direct specific requests to those new components.
Beginning the Strangler Pattern Migration
If you’ve completed the planning stage, including a thorough application modernization assessment, you will have selected the first set of components you want to migrate. Otherwise, take time to identify the applications—or even specific sections of code within the monolith—that are most in need of modernization. Since Strangler pattern migration occurs piece by piece, it’s important to prioritize the movement of inefficient, complex, or high-risk components, as well as applications with significant technical debt.
You can leverage a number of strategies to reroute traffic as migrations begin. Companies commonly create URL path-based routing rules, but you can also direct users based on headers, cookies, and other request properties.
This diagram shows how the proxy layer will start to reroute to newer components as rules are established:
Eventually, when all your applications are migrated, you’ll be able to retire your legacy system as well as the proxy layer.
Monitoring and Testing During Implementation
Since Strangler pattern implementation can be a complex process, it’s essential to actively ensure system stability. Monitoring performance and functionality can help you pinpoint and remediate any degradations in service.
At the start of your Strangler pattern migration, establish a baseline for your existing applications, measuring key metrics like response times, error rates, and resource utilization. These benchmarks will allow you to compare the performance of new components. Once you’ve taken this first step, you can leverage various tools to monitor your modernized applications, such as:
- Prometheus, Amazon CloudWatch, and Grafana, which monitor applications and alert you of performance changes.
- AWS X-Ray, which can help analyze and debug applications.
- Azure Monitor and AWS CloudTrail, which can log user activity so you can correlate events across all parts of the system.
Automated testing and regular optimization are crucial for maintaining confidence as you gradually replace legacy components. Your thorough efforts will ensure more reliable and maintainable applications as your migration concludes.
Establishing a Feedback Loop
Establishing a robust feedback mechanism can help you make iterative improvements throughout the Strangler pattern migration process—beyond the suggestions monitoring tools may provide. With clear “checkpoints” in place, you can ultimately ensure a smoother transition to your future-proof system and applications.
Here are some examples of strategies organizations implement to ensure continuous, internal feedback loops:
- Pair programming, which occurs when two developers use the same workstation, with one writing the code and the other reviewing it. This Agile technique allows for instant peer feedback.
- Test-driven development, in which developers write tests before the actual code. Each time you save a code file, you’ll be able to get quality feedback.
- Static analysis, which allows you to examine code bases and debug without executing an entire program.
Getting regular user feedback regarding usability, functionality, and any disruptions experienced during the transition is also key to seamless migration.
Most feedback loops can be automated, at least in part. However, getting quantitative data and analytics from machine learning and AI tools should not fully replace human decision-making. DevOps teams should hold regular meetings—both internal and cross-functional—to transparently discuss findings, share lessons learned, and collaboratively brainstorm solutions. This approach not only accelerates problem-solving but also encourages continuous improvement and innovation.
Advancing Your Strangler Pattern Migration
Strangler pattern migration requires a detail-oriented approach. Once a proxy layer is implemented—leveraging technologies that are best-suited for your infrastructure and applications—it’s important to continuously monitor and test a wide range of metrics. Ongoing iterations are key for smooth transitions to future-proof applications. Partnering with application modernization experts can ensure quality migrations while accelerating your holistic digital transformation.
Stay tuned for the next article in our series, which will cover advanced strategies for Strangler pattern implementation, including best practices for managing complex dependencies and security considerations.