Modernising a legacy AS/400 (IBM i) system without rewriting it

Short summary

A practical guide to modernizing legacy AS/400 (IBM i) systems without rewriting them, advocating the 'strangler fig' pattern. The article recommends exposing RPG programs and DB2 databases behind modern APIs (e.g., Spring Boot), then building web interfaces with React on top. This incremental approach preserves decades of refined business logic while solving isolation, skills, and security problems step by step.

• •Rewriting legacy AS/400 systems from scratch is riskier than modernizing incrementally
• •Use the strangler fig pattern: expose RPG/DB2 behind APIs, then build modern UIs on top
• •Each modernization step delivers value independently and can be paused without risking the core system

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