Step 03 of 10 8-12 weeks· advanced
Step 3: Target Architecture Design
Design the modern target — including the 5250 UI strategy, which is the IBM i-specific architectural decision that drives much of the rest.
Recommended prompts
Use one of these to do the work in your IDE
Open the template to read it in full. Click Copy prompt to grab it (with your stack values pre-filled where they apply) — then paste into Claude Code, Cursor, or wherever you build.
Recommended skills
Drop these into Claude Code for this phase
Skills auto-trigger on the right kind of request. Install once; they apply to every prompt that fits.
Recommended MCP configs
Wire these tools into Claude Code first
MCP servers give Claude Code direct access to external systems (Jira, browsers, databases). Configure once.
When you're done
Verify these in your own work before moving on
This is a checklist for you to mentally tick off in your repo and IDE — the site doesn't track it, you do.
- Target architecture documented end-to-end
- Monolith vs microservice decision with rationale
- 5250 UI strategy decided (replace / hybrid / mobile-first / Profound UI)
- Database strategy decided
- Batch architecture decided (Spring Batch / Step Functions / Airflow)
- Online architecture decided (REST / GraphQL / event-driven)
- Mobile strategy if applicable
- Auth approach decided
- Cloud / hybrid decision made
- 10-15 ADRs documenting key decisions
- Operational model defined
Common pitfalls
What goes wrong at this step
- Premature microservices — RPG monoliths often work because of library-list-isolated transaction integrity
- Treating 5250 → web as an afterthought — UI redesign is its own significant work
- Skipping the mobile question — field workers / shop floor / sales reps have mobile use cases
- All-in on bleeding-edge tech — RPG stack was stable for decades; new stack should also bias toward stability