Application modernization

Moving legacy applications forward without a rewrite that never lands.

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What is it?

Full rewrites have a poor track record: they take longer than promised and the old system keeps changing underneath. We prefer incremental modernization, carving functionality out of the legacy application piece by piece while it stays in production and keeps earning.

For a technical reader

The default pattern is the strangler fig: place a facade in front of the legacy application, route one capability at a time to new implementations, and shrink the old system until retiring it is uneventful. The constraint is usually data, not code. Two systems writing the same tables cannot be separated until ownership is split, so the sequencing question is which data each extracted capability owns and how consistency is maintained during the overlap.

Our services

Modernization assessmentEach application scored on business value, change frequency and technical risk, with a recommendation to modernise, replace, re-platform or leave alone.
Incremental migration deliveryCapability-by-capability extraction with the legacy system live throughout.
Data decouplingSplitting shared database ownership, usually the hardest and most-skipped part.
DecommissioningRetiring legacy components with evidence that traffic and data have genuinely moved.

What’s covered

Strangler-fig routing
A facade in front of the legacy app so traffic moves to new code path by path
Monolith decomposition
Carving out bounded contexts that can be deployed and scaled independently
Database decoupling
Breaking the shared database that usually blocks any real separation of services
Legacy interfaces
Mainframe, AS/400 and older middleware wrapped behind modern APIs
Re-platforming
Moving workloads to containers or managed services where a rewrite is not justified

Business problems we solve

Changes take monthsTight coupling means every change risks something unrelated. Extracting bounded capabilities shrinks the blast radius.
The platform is out of supportUnsupported runtimes and databases are a security and audit problem. Re-platforming can address that without a full rewrite.
Only two people understand itKey-person risk. Extraction plus documentation spreads that knowledge as a side effect.
A rewrite was attempted and stalledBig-bang rewrites fail because the old system keeps moving. Incremental extraction delivers value from the first slice.

Our delivery approach

  1. 01
    Assess honestlySome systems should be modernized, some replaced, and some left alone. We say which is which before anyone commits budget.
  2. 02
    Put a seam inA routing layer in front of the legacy system lets new functionality be served from new code without the caller knowing or caring.
  3. 03
    Migrate by sliceOne capability at a time, each released and verified. The legacy system shrinks rather than being switched off in one event.
  4. 04
    Decommission deliberatelyOld paths come out once traffic is proven to have moved, with the evidence to show it.

Solutions & project types

Examples of the work we take on in this area. These describe project shapes, not named client engagements.

Monolith to servicesExtracting high-change capabilities from a large application so they can be deployed independently.
Mainframe facadeExposing mainframe functions through APIs so new channels can be built without touching COBOL.
On-premises to cloud re-platformMoving a workload to managed infrastructure with minimal code change where a rewrite is not justified.
Database migrationMoving off an end-of-life or expensively-licensed database with a tested cutover.

Technologies & platforms

Patterns

  • Strangler fig
  • Anti-corruption layer
  • Branch by abstraction
  • Change data capture

Runtime targets

  • Kubernetes
  • AWS ECS
  • Azure App Service
  • Oracle Cloud Infrastructure

Data

  • PostgreSQL
  • Oracle Database
  • SQL Server
  • Debezium
  • AWS DMS

Legacy interfaces

  • SOAP / WSDL
  • IBM MQ
  • CICS
  • AS/400
  • Flat file batch

Verification

  • Contract tests
  • Traffic shadowing
  • Reconciliation jobs
Learn this field

Where to start with application modernization.

Secondary to the work itself, but genuinely useful if you are building the skill. Every link goes to official documentation or an official channel.

Beginner

  • Read and safely change unfamiliar code
  • Characterisation tests around untested behaviour
  • Basic refactoring moves and when they are safe
  • Version control discipline on long-lived work

Intermediate

  • Strangler fig and anti-corruption layer patterns
  • Domain-driven design and bounded contexts
  • Change data capture and dual-write pitfalls
  • Feature flags and branch by abstraction
  • Traffic shadowing to compare old and new

Advanced

  • Splitting a shared database without downtime
  • Distributed consistency during a migration window
  • Data reconciliation and provable cutover
  • Sequencing a multi-year programme so value lands early

Certifications

  • AWS Certified Solutions Architect – Professional
  • Microsoft Certified: Azure Solutions Architect Expert
  • Oracle Cloud Infrastructure Architect Professional

Practice projects

  • Put characterisation tests around a module before changing it
  • Route one endpoint through a facade to a new implementation
  • Use change data capture to keep two stores in step during a migration
  • Shadow production traffic to a new service and diff the responses
  • Write a reconciliation job proving both systems agree before cutover
FAQs

Questions we get asked.

Is a rewrite ever the right answer?

Occasionally — small systems, or where the domain has changed so much the existing model is wrong. For anything large and actively used, incremental extraction has a far better record.

How long does this take?

It depends on coupling and how much the legacy system still changes. The point of the incremental approach is that you get working slices throughout rather than waiting for one date.

Can we modernise and add features at the same time?

Yes, and usually you must, because the business will not pause. The sequencing just has to account for it rather than pretending there is a freeze.

What if the legacy system has no tests?

That is the normal starting position. We add characterisation tests around current behaviour first, so there is something to verify against before anything moves.

Engineering

Related services.

Cloud-native developmentServices built to run on cloud infrastructure from the first commit, not lifted onto it later.Platform engineeringThe internal foundations that let your product teams ship without re-solving infrastructure each time.API & systems integrationMaking systems that were never designed to talk to each other exchange data reliably.Quality & test automationA test suite teams trust enough to deploy on, rather than one they routinely skip.
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