You're facing a legacy system migration. How do you decide which components to move to microservices first?

Migrating legacy systems to microservices is a complex process because it adds huge management overhead. Start with Low-Risk Targets: Begin with isolated services like email notifications. Protect Core Functionality: Avoid rushing to migrate critical components like core banking systems. Build a Solid Foundation: Ensure initial microservices are robust before expanding. Expand Incrementally: Gradually migrate other components. Don't touch the central system until confident. Monitor Continuously: Evaluate migrated services and adjust strategy as needed. Microservices require careful management and independent optimization. Sometimes, leaving legacy components unchanged is best if migration costs more than benefits.

1. Separation of Concerns - Identify the critical and independent services. Migrate them first and evaluate the system's performance and stability. 2. Group the Services by Business Units or Processes - Identify the services' business impact and migrate them from high to low. 3. Review the low-impact services and decide whether to migrate or sunset.

It is very important to evaluate: - How critical is the component ? how pain it wold cost to your company some failure or miss behaviour for particular component? - which classes/services have more integration tests and could be easily verified in a new system; - How efficient is the communication between the support and operation team ? how efficiently your deploy strategy is to roll back to previous implementation component?

Start by identifying pain points in your system, such as components that are difficult to scale or update. Migrating these to microservices can quickly address key issues. Focus on modules with frequent updates or performance bottlenecks. This targeted approach showcases microservices’ benefits early on, gaining stakeholder support and momentum.

Evaluate dependencies between components in your legacy system. Components with fewer dependencies are easier to migrate since they require less coordination. Use dependency graphs to visualize connections and identify independent services. Migrating these simpler components first streamlines the process and sets a foundation for tackling more complex parts in later stages.

Additionally, when planning a legacy system migration, it's crucial to integrate security considerations early in the process. Each microservice introduces new attack surfaces, so securing communication between services is paramount. Implement strong authentication and authorization protocols, such as OAuth or JWT, to control access to each microservice. Additionally, consider encrypting data both in transit and at rest, and employ network segmentation to limit potential lateral movement within the system. Regularly update your threat model to reflect the new architecture, and use automated security testing tools to identify vulnerabilities as part of your continuous integration pipeline.

Next up, take a good, hard look at the dependencies between your system's components. The more tangled up they are, the trickier it gets. Components with fewer ties are way easier to break off because they don’t drag the rest of the system with them. Grab a dependency graph. It’s your map of how everything’s wired together. This will show you which parts are more isolated and ready to break free. Start with those cleaner, less connected bits. They’ll be smoother to migrate and give you a good blueprint for dealing with the gnarlier, intertwined parts later on. Small wins, clear patterns, fewer headaches.

Prioritize migrating components that would gain the most from microservices’ scalability, like those handling variable loads such as user authentication or payment processing. Scaling these components independently delivers immediate performance boosts and cost savings. This approach also validates microservices' effectiveness in managing dynamic workloads, proving their value early in the migration.

When thinking about scalability, zero in on the components that struggle with fluctuating loads—like user authentication or payments. These are prime candidates for microservices because you can scale them without touching the rest of the system. Migrating these high-demand areas first gives you immediate wins: faster performance, reduced costs, and the ability to handle dynamic workloads more efficiently. Plus, it’s a great way to prove the power of microservices early in the process. By tackling these key services, you set the stage for a system that scales easily, runs smoother, and flexes with your business needs.

Tendo em vista que a arquitetura de microsserviços irá promover maior escalabilidade, flexibilidade e agilidade no desenvolvimento e na entrega de novas funcionalidades, a avaliação de quais componentes geram mais valor para o negócio se implementados com a arquitetura de microsserviços é crucial.

When evaluating what to migrate, always consider the business value of each component. Prioritize the pieces that directly impact operations or customer experience—those are your heavy hitters. Start with high-impact areas to deliver quick wins and show real value from the get-go. This makes the migration investment clear to everyone, especially the stakeholders. By aligning your migration efforts with business goals, you ensure that the most critical parts of the system get the microservices upgrade first. This approach keeps the focus on what really matters: driving value and making sure your system stays in sync with business needs.

- Describe your use case scenarios and ask AI tools such as ChatGPT to provide additional test cases; - Priorize integration tests that could be executed regarding codebase. - Consider to monitor the test coverage measure on the new system version to increase the confidence on the system migration.

As you migrate components, a solid testing plan is crucial to ensure everything runs smoothly. The goal is to maintain system integrity and preserve user trust by catching issues before they escalate. Your testing plan should cover all bases: start with unit tests for individual functions, move to integration tests to check how services interact, and finish with end-to-end tests to validate the entire workflow in the new architecture. A well-thought-out testing strategy will help you detect problems early, minimizing risks and disruptions during migration. It’s about protecting both system stability and the confidence users have in your product.

- Subscribe to a great APM tool and manager error rate, response time and other metrics - Create a KPI dashboard to monitor whether some implemantion error could impair some business indicator. - Take release notes in each deploy and make it available to all support and operation members; - make post-mortem for critical incidents and provide action plans to mitigate similar problems in future.