Monolith to Microservices Interview Questions for Engineering Managers

Common Monolith-to-Microservices Interview Questions

These questions evaluate your experience with and approach to one of the most challenging architectural transformations in modern software engineering.

• Describe your approach to migrating a monolithic application to microservices.
• How do you determine which parts of a monolith to extract first?
• How do you maintain feature delivery during a large-scale architectural migration?
• What are the biggest risks in a monolith-to-microservices migration, and how do you mitigate them?
• How do you handle data migration and database decomposition during the transition?

What Interviewers Are Looking For

Interviewers want to see that you approach migrations pragmatically, with clear business justification and risk management rather than architectural idealism. They are looking for evidence that you can plan incremental migration strategies, maintain delivery during the transition, and make disciplined decisions about what to extract and what to leave.

Strong candidates demonstrate familiarity with migration patterns like the strangler fig, show awareness of the data decomposition challenge, and can discuss how they maintained both the old and new systems during the transition period. They also show that they measure migration success through business and operational outcomes, not just architectural purity.

• Clear business justification for the migration beyond architectural preference
• Incremental migration strategy with measurable milestones and decision points
• Risk management including rollback plans and dual-running capabilities
• Realistic approach to data decomposition and shared database challenges
• Ability to maintain feature delivery and team morale during a multi-month migration

Framework for Structuring Your Answers

Structure your answers around the migration lifecycle: assessment (evaluating whether migration is justified and identifying extraction candidates), planning (defining the migration strategy, sequence, and milestones), execution (implementing the migration incrementally with continuous validation), and stabilisation (ensuring the new architecture is operational and performant). This lifecycle approach demonstrates comprehensive migration thinking.

Emphasise the strangler fig pattern - incrementally replacing monolith functionality with microservices while both systems run in parallel. This demonstrates pragmatism and risk awareness, which are more impressive to interviewers than theoretical knowledge of architectural patterns.

Example Answer: Leading a Monolith Decomposition

Situation: Our eight-year-old monolithic application served 2 million users but had become a significant bottleneck. Deployment required full-team coordination, a single bug could affect all features, and scaling required scaling the entire application even when only one component was under load.

Task: I needed to plan and execute a migration to microservices that would resolve these pain points without disrupting our product roadmap or degrading the user experience.

Action: I began with a domain analysis, working with the team to identify bounded contexts within the monolith. We identified 12 potential services, then prioritised extraction based on three criteria: deployment frequency need, independent scalability requirement, and clear domain boundary. Our first extraction target was the notification service - it had a well-defined interface, high change frequency, and minimal data coupling. We used the strangler fig pattern, routing notification requests to the new service while keeping the monolith implementation as a fallback. I allocated 30% of team capacity to migration work while maintaining 70% on feature delivery. We established a migration dashboard tracking both technical progress and operational health metrics.

Result: We successfully extracted four services in the first year, reducing monolith deployment coordination from a full-team event to independent team releases. Deployment frequency for extracted services increased from weekly to multiple times daily. The notification service handled a three-times traffic spike during a marketing campaign by scaling independently, something that previously would have required scaling the entire monolith. We maintained our feature delivery commitments throughout the migration, which was critical for maintaining stakeholder confidence.

Common Mistakes to Avoid

Migration questions reveal your pragmatism and risk management skills. Avoid these mistakes.

• Attempting a big-bang rewrite rather than an incremental migration strategy
• Not establishing clear business justification and success metrics for the migration
• Underestimating the data decomposition challenge and shared database dependencies
• Pausing all feature delivery during migration, losing stakeholder confidence
• Extracting too many services too quickly without building operational maturity

Key Takeaways

• Demonstrate incremental migration strategies with clear business justification
• Show risk management through patterns like the strangler fig and dual-running systems
• Present data decomposition as a first-class challenge requiring careful planning
• Emphasise maintaining feature delivery alongside migration work
• Connect migration outcomes to measurable business and operational improvements