RPG / IBM i Modernization Playbook

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Steps you'll go through

1. 01

   Audit and Inventory

   6-12 weeks

   Inventory programs, service programs, modules, CL programs, DDS / SQL files, display files (5250), job streams, data, environment dependencies, and people.

2. 02

   Business Rule Extraction

   3-6 quarters (the longest phase)

   Convert each in-scope RPG program (and CL program) into structured business rule catalogs — including indicator analysis, the most RPG-specific concern.

3. 03

   Target Architecture Design

   8-12 weeks

   Design the modern target — including the 5250 UI strategy, which is the IBM i-specific architectural decision that drives much of the rest.

4. 04

   Data Migration Design

   8-12 weeks

   Plan how DB2 for i moves to a modern relational target. DB2 for i is more migration-friendly than VSAM/IMS but has its own quirks (multi-member files, logical-file roles, DDS extensions, CCSID, journaling).

5. 05

   Build the Coexistence Layer

   8-12 weeks

   Bridge IBM i and the new system: API gateway, data sync, federated auth, observability that spans both worlds. Easier than mainframe coexistence — IBM i has good ODBC/JDBC drivers and Integrated Web Services.

6. 06

   Migrate the First Capability (Vertical Slice)

   4-6 months for the first slice

   Ship one complete capability through the new stack. For RPG specifically, slice 1 should be read-only or low-stakes with limited 5250 redesign — exercise the infrastructure, not the riskiest UX.

7. 07

   Continue Migrating Slices

   1-3 years (the dominant phase)

   Migrate the remaining capabilities — backend, UI, and tests in parallel. Track progress visibly: % programs migrated, % transactions on new, % 5250 screens replaced, % users on new UI.

8. 08

   Decommission IBM i

   4-12 months

   Turn off IBM i. Sequence: read-only IBM i → selective subsystem shutdowns → data archive → hardware decommission (or contract termination if PowerVS) → license cancellation.

9. 09

   Workforce Transition

   Throughout the program, intensifying in the last 6-12 months

   Capture institutional knowledge before retirement; retrain transferable RPG developers; transition operations; lead the culture change. Failed modernizations often fail here.

10. 10

    Post-Migration Validation and Optimization

    6-12 months post-cutover

    Verify the modernization actually delivered (cost, performance, reliability, agility, compliance). Then optimize the parts that were rushed.