Migration Risk
Bounding blast radius, staging by cohort, and honest readiness reporting.
6 to work through
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intermediate
Review this migration plan. Cutover is staged by customer cohort at 2 percent then 10 then 50 then 100. Readiness for each step is "all automated tests green and no open P1 defects". The rehearsal ran against a 5 percent copy of production. The rollback step reads "restore from the pre-cutover snapshot if data integrity is compromised". What would you remove, what would you change, and what would you leave alone?
3 min answer -
intermediate Multiple choice
What is the single most important risk control in a migration, and why?
2 min answer -
intermediate
You want to replace a twelve-year-old monolith one capability at a time. The organisation releases that monolith once every six weeks on a Thursday evening, behind a change advisory board that meets fortnightly. Tell me what you would do first and why.
3 min answer -
advanced
A logistics platform is migrating a system that coordinates live vehicle dispatch. What controls reduce migration risk when the operation cannot pause?
2 min answer -
advanced
A platform is migrating a live service and must manage risk. Which risks dominate, and which controls actually reduce them?
2 min answer -
advanced
Ant Group moved Alipay's core transaction data off a commercial relational database onto OceanBase, its own distributed database, beginning with a 1% slice in 2014 and reaching full replacement in 2019. What risk control is that ramp actually providing, and where would copying it be a mistake?
3 min answer
3 terms in this topic
Cutover Abort Criteria
Numeric thresholds agreed before a cutover with one named person empowered to apply them, which replaces an improvised 03:00 judgement made by the pe…
practiceMigration Risk
The specific risks migrations carry, and the controls that reduce each — with reversibility as the master control.
practiceMigration Risk Register
A maintained record of what could go wrong in a migration, with likelihood, impact, owner and mitigation, reviewed as the programme progresses.
Neighbouring topics
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.
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.