Legacy modernization
On this page 9 topics
Overview
Topics
- Rehost
- replatform
- refactor
- replace
- retire
Learn first
4 h of practice (estimate)
Learning outcomes
- Apply the modernization options — rehost, replatform, refactor, replace, retire (and retain) — per application.
- Assess legacy applications by business value, technical condition, risk, and cost to change.
- Sequence modernization to deliver value early and reduce risk (strangler, coexistence).
- Build the business case for modernization.
Lessons
Lab and exercises
Lab
ARC-010-LAB1 · Portfolio disposition
Outcomes: 1–4 · Time: ~4 h
- Build an evidence sheet for the Larkspur applications: web shop, store POS integration, order management in ERP, CRM, reporting.
- Score value, condition, risk, and cost to change; plot the quadrant.
- Assign a disposition (rehost, replatform, refactor, replace, retire, retain) to each.
- Sequence the dispositions with coexistence and dependency notes.
- Write a short business case for the largest change.
Acceptance: each decision justified by value, condition, and risk.
Exercises (case-based; six exercises)
| ID | Outcome | Task |
|---|---|---|
| ARC-010-EX01 | 1 | Assign dispositions to six Larkspur applications and justify each in one sentence. |
| ARC-010-EX02 | 1 | A team proposes to rehost the web shop to the cloud to "go modern". Assess the proposal. |
| ARC-010-EX03 | 2 | Score three applications on value, condition, risk, and cost to change using a supplied evidence sheet and plot them. |
| ARC-010-EX04 | 3 | Design a strangler sequence for moving web traffic from the old shop to the new platform in three slices. |
| ARC-010-EX05 | 3 | Define system-of-record rules during coexistence for products, customers, and orders. |
| ARC-010-EX06 | 4 | Write a one-page business case for replacing the web shop with "do nothing" as the baseline. |
Show solutions
- EX01 Web shop: replace; ERP order management: retain and wrap; CRM: retain or replatform; reporting: replatform to a managed analytics service; store POS integration: refactor behind the new interface; old label tool: retire.
- EX02 Rehosting moves the problem; the shop's issues are agility and mobile support, which hosting does not fix. Prefer replace; rehost only as a short bridge if infrastructure is the urgent risk.
- EX03 Show scores with evidence references; high value/low condition first for action; low value/low condition for retirement.
- EX04 Slice 1: browse and checkout for web; slice 2: mobile and accounts; slice 3: store pickup and returns; route by feature flag or gateway; retire the old shop when traffic reaches zero.
- EX05 Products owned by merchandising source, orders owned by the new platform until posted to the ERP, finance records owned by the ERP, customers by CRM with sync; one owner per entity at any time.
- EX06 Baseline "do nothing" shows rising run cost and lost sales; option replace shows migration cost, dual running, benefits with ranges, payback; list assumptions and sensitivity.
Workplace evidence: a modernization decision you led or shaped and its result.
Quiz
Outcomes: O1 disposition options · O2 portfolio assessment · O3 sequencing and coexistence · O4 business case.
A self-check for you: nothing is graded, saved or sent anywhere. Choose an answer, then check it. You can try again as often as you like.
Practical part
Disposition defense using the lab evidence sheet and decisions plus exercises ARC-010-EX01 to EX06. Pass: quiz at least 8/10, at least five of six exercises correct, and each disposition justified by value, condition, and risk.
Common mistakes
Rewriting everything; rehosting without addressing the reason for moving.
Assessment
Disposition defense.
Workplace evidence
A modernization decision you led or shaped and its result.
Career relevance
Migration strategy (ARC-037).