Migrating to Microservices

1. Assessing Monolith Architecture

Question	Detail
Pain points?	Deploy speed, team coupling, scaling
Domains?	Bounded contexts
Data coupling?	Shared tables, FKs
Don't decompose	If monolith works fine

2. Identifying Service Boundaries

Method	Detail
Event Storming	Domain events → aggregates
Team topology	Conway's Law alignment
Business capability	Per capability service

3. Using Strangler Fig Pattern

Step	Detail
Façade	Proxy in front of monolith
Route	New endpoints → new service
Migrate	One capability at a time
Decommission	Old code when traffic = 0

4. Implementing Anti-Corruption Layer

Aspect	Detail
Translates	Legacy model ↔ new domain
Isolates	New service from legacy quirks
Removed when	Legacy retired

5. Extracting Services Gradually

Order	Detail
Edge first	Read-only, low-risk
Then writes	Outbox + dual-write
Finally core	When confidence is high

6. Managing Data Migration

Step	Detail
Dual-write	Write to old + new
Backfill	Historical via CDC
Read switch	Shadow then cutover
Decommission	Stop dual-writes

7. Implementing Feature Parity

Practice	Detail
Inventory features	Old → new mapping
Acceptance tests	From legacy behavior
No new features	Until parity

8. Testing During Migration

Technique	Detail
Shadow / mirror	Compare outputs
Diff tooling	scientist-style
Canary	Slow traffic shift

9. Managing Team Transition

Element	Detail
Team topologies	Stream-aligned, platform, enabling
Skill gaps	Training: K8s, observability
On-call	You build it, you run it

10. Handling Rollback Scenarios

Tactic	Detail
Feature flag	Flip back to monolith path
Façade route	Revert routing rule
Keep dual-write	Until cutover trusted

11. Using Branch by Abstraction

Step	Detail
Add abstraction	Interface around old impl
New impl	Behind same interface
Switch	Flag-driven swap
Remove old	Once stable

12. Implementing Parallel Run Strategy

Aspect	Detail
Both run	Old + new on every request
Compare	Log diffs to investigate
Authoritative	Old until new proven
Risk	Side-effects must be idempotent