Zero-Downtime Migration
Expand, migrate, contract — and the contract phase that never happens.
4 to work through
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intermediate Multiple choice
A commerce platform must change a database schema while an older application version is still running. What migration pattern prevents downtime, and what is the common mistake?
2 min answer -
advanced Multiple choice
A hot table needs a column renamed and retyped, across many running instances. What constraint dictates the whole sequence?
2 min answer -
advanced
A large sharded MySQL fleet needs a tenant moved between shards with no downtime. How should online data movement, dual writes, cutover and rollback be sequenced?
2 min answer -
advanced
A platform deploying many times a day must change a column type on a very large table with no maintenance window. Walk through the sequence.
2 min answer
3 terms in this topic
Expand-Contract Migration
Making a breaking change as a sequence of individually reversible steps - add the new alongside the old, migrate readers and writers across, then rem…
practiceZero-Downtime Cutover
Moving a live system to a new implementation or datastore without an outage, using dual writes, backfill and a reversible traffic switch.
practiceZero-Downtime Deployment in Practice
Shipping without a maintenance window, and the version-skew constraint that governs every schema and contract change.
1 artifact you would hand over
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.
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.
Migration Risk
Bounding blast radius, staging by cohort, and honest readiness reporting.
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.