Legacy Modernization
Real-world architecture is usually about improving systems that already exist.
20 topics in this area.
Each topic is the unit content is filed against. Topics with nothing in them yet are shown too — they are the honest edge of the curriculum rather than a gap being hidden.
Legacy Modernization
General material on modernising existing systems.
Legacy Assessment
Understanding what a system does before deciding what to do with it.
The Six Rs
Rehost, replatform, refactor, repurchase, retire, retain — per application.
Rehosting
Lift and shift: fastest, cheapest, and capturing none of the benefits.
Replatforming
Targeted changes that capture operational wins without a rewrite.
Refactoring & Re-architecting
Changing structure incrementally while the system keeps running.
Rebuild vs Re-architect
Why greenfield replacement fails, and the narrow cases where it does not.
Strangler Fig
Routing capabilities to new implementations behind a facade, one at a time.
Application Decomposition
Finding seams in a monolith, starting from the data.
Database Migration
Moving engines, versions and schemas without losing data or uptime.
Data Migration Strategies
Backfill, dual-write, reconciliation and verification.
Zero-Downtime Migration
Expand, migrate, contract — and the contract phase that never happens.
Parallel Run
Shadowing the old system to discover the rules nobody documented.
Cutover Planning
Rehearsals, go/no-go criteria and a rollback that has been executed.
Legacy Integration Patterns
Anti-corruption layers, adapters and CDC against systems that cannot change.
Mainframe Modernization
Batch windows, COBOL, and the risk profile of core banking systems.
Migration Risk
Bounding blast radius, staging by cohort, and honest readiness reporting.
Modernisation Business Case
Pricing tail risk so deferred maintenance becomes fundable.
Coexistence Patterns
Running old and new together for years without corrupting either.
Decommissioning
Actually switching the old system off, and proving nothing depended on it.