Mainframe Modernization
Batch windows, COBOL, and the risk profile of core banking systems.
5 to work through
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advanced
A core system is reliable, undocumented and staffed by people close to retirement. What do you do first?
2 min answer -
advanced
An organisation must modernise a mainframe system running critical batch processes. What makes this harder than typical modernisation, and what approaches exist?
2 min answer -
advanced
Customer balances are served from a change-data-capture copy of a mainframe rather than from the mainframe itself. What happens, hour by hour, on the night the month-end close posts a large batch and the capture stream falls forty minutes behind?
3 min answer -
advanced Multiple choice
Review this plan. A bank will move 80% of balance-enquiry reads off the mainframe onto a new store fed by change data capture. The nightly batch that posts interest and produces statements stays where it is for three more years. The business case is built on the licence saving. One reviewer says the headline saving will not appear. Which objection is correct?
3 min answer -
advanced
You must modernise a mainframe application with no documentation and one remaining expert who retires in nine months. Where do you start?
2 min answer
3 terms in this topic
Mainframe Modernisation
Replacing or reducing dependence on a core system that is reliable, undocumented, and central to the business.
patternMainframe Offload
Moving read traffic and selected processing off a mainframe onto modern platforms, reducing cost and unblocking new development without replacing the core.
patternOffload Freshness Contract
An explicit published staleness budget for a read copy that serves traffic taken off a core system, enforced by the copy itself, so that silently sta…
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.
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.