Monolith to Microservices Migration: A Pre-Flight Checklist

Most monolith-to-microservices migrations fail not because the architecture is wrong, but because teams underestimate how much preparation the transition requires. The technical work of extracting services is often the easier part. The hard part is everything that has to be true before you extract the first service — infrastructure readiness, domain clarity, and organizational alignment.

This checklist is built for engineering teams about to start a migration, or teams who are mid-migration and want to verify they have covered their bases.

Readiness Checklist: Before You Extract Anything

Organizational and process prerequisites

• The team understands that this is an incremental migration, not a project with a single go-live date
• There is an explicit owner for the migration effort who has authority to make architectural decisions
• Product stakeholders understand that some feature work will slow during the transition
• On-call and incident response processes are updated to handle a distributed system (routing, service isolation, cascading failures)

Infrastructure prerequisites

• A container runtime (Docker) and an orchestration layer (Kubernetes or equivalent) are in place and the team is trained on them
• A CI/CD pipeline can deploy individual services independently
• Centralized logging aggregates logs from multiple services into one place
• Distributed tracing is configured so you can follow a request across service boundaries
• A secrets management system handles credentials per-service (not hardcoded or shared via environment files)

Codebase prerequisites

• The monolith has been audited for domain boundaries using domain-driven design principles
• A dependency graph of the monolith's internal modules exists and is reasonably current
• Test coverage on the monolith is sufficient to detect regressions when behavior moves to new services
• The database schema has been reviewed and tables owned by specific domains have been identified

Decomposition Checklist: Choosing Your First Services

Selecting the right starting candidates

• The first extraction target is a peripheral capability, not a core business flow
• The candidate service has a well-defined API surface (clear inputs and outputs)
• The candidate service owns a bounded set of data — it does not read from dozens of tables shared with the rest of the monolith
• The candidate service is not on the critical path for revenue or a compliance obligation

Defining service contracts

• The new service's API contract is documented before implementation begins
• Contract tests are written that both the monolith and the new service can run against
• Versioning strategy for service APIs is decided (URL versioning, header versioning, etc.)

Data Migration Checklist

Data is where migrations most commonly stall or break. Work through this section carefully.

• Tables owned by the target service are identified and separated logically (if not physically yet)
• A data backfill strategy exists for populating the new service's datastore from legacy data
• A dual-write or event-sync mechanism is planned for the transition period where both systems are live
• Data validation jobs exist to compare record counts and checksums between source and target
• A rollback plan for data is documented — what happens if you need to revert after partial migration

Go-Live Checklist: Routing and Cutover

• A facade layer (API gateway or reverse proxy) is in place and routing 100% of traffic to the legacy path as a baseline
• The new service has been dark-launched (called in parallel, output compared, results discarded)
• Error rates and latency benchmarks are established for the legacy path so regressions are detectable
• Traffic is being shifted incrementally (10% → 25% → 50% → 100%) with monitoring at each step
• A feature flag or routing rule allows instant rollback to the legacy path
• Retirement criteria for the legacy path are written and agreed upon before cutover begins

Post-Migration Checklist: After Each Service Extraction

• The legacy code path for this capability has been removed (not just disabled)
• Dead tables no longer written to by the monolith have been archived or dropped
• Documentation for the new service exists: what it does, who owns it, how to deploy it, how to debug it
• The on-call runbook for this service is written and tested
• The facade routing rule for this capability is cleaned up

The One Thing Teams Most Often Skip

Retirement. Teams extract a service, shift traffic, declare victory, and never remove the legacy code path. Months later they are maintaining two systems. Write the retirement criteria before you extract anything, and treat retiring the legacy path as a hard deliverable, not an optional cleanup task.

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Building this kind of migration is detailed, high-stakes work. If you want an experienced team to help you scope, sequence, and execute it, start a conversation with Clixo.