Application Modernization Services for US Product Teams
Siblings Software provides application modernization services when a US product team must pull one capability out of a .NET or Java monolith, publish a stable API, and route live traffic while the rest of the product keeps shipping. The buyers are VP Engineering, architecture owners, and platform leads at B2B SaaS, equipment finance, and mid-market software companies whose release train still touches one deployable. This page covers service scope, who it fits, typical slices, delivery phases, squad shape, pricing inside published bands, comparisons with hiring and freelancers, a labeled example, risks, and questions to ask before a discovery call.
Account work runs from our Miami office. Engineering is delivered from Latin America with daily overlap on US East Coast hours. Patterns follow Martin Fowler's strangler fig, the .NET Upgrade Assistant when a Framework upgrade is in scope, and OpenAPI 3.1 for partner contracts. Moving VMs is a different job: see cloud migration services. Ongoing APIs live under API development and back-end development.
Reviewed by Javier Uanini, Founder and CEO, September 2026.
What the Service Covers
Application modernization services are the engineering work of shrinking a monolith one capability at a time. A slice starts with a seam map: which modules, tables, batch jobs, and callers move together. It continues with an anti-corruption layer so the new service does not inherit every stored-procedure quirk, an OpenAPI contract for the first consumers, feature-flagged routing at a gateway or reverse proxy, and a reconciliation job when both paths can write. The handoff is a runbook your team uses for the next slice.
That work is different from cloud migration services, which inventory workloads, build landing zones, and rehearse DNS cutover. A lift into AWS can leave the same tangled deployable in a new account. It is also different from a greenfield back-end development engagement, which designs new services when there is no production monolith to keep alive. Modernization keeps the current release train earning revenue while one path moves.
Stack work we take on includes .NET Framework to modern .NET, Java Spring module extraction, and PHP or Node admin UIs that should call the new API instead of the old controllers. For a published .NET delivery reference, see the Bari wholesale platform case study. Quality gates use contract tests in CI and, when the suite is large enough to need its own owners, QA automation services.
The diagram shows what a buyer receives at each step: a seam list, a reviewed OpenAPI spec, a canary route with a rollback flag, and repositories that stay in the client's org.
Who It Is For
US product and platform teams whose monolith still ships revenue, whose shared database blocks a second squad, and whose leadership wants a production route this year. If nobody can name the first module and the person who pages when that route fails, this engagement is the fit.
Equipment finance and leasing
Contract, residual, and invoice logic live in one .NET deployable. Dealers want APIs. Month-end close still runs inside the monolith. The first slice is the contract read API, not a full ledger rewrite.
B2B SaaS with one release train
Every feature waits on the same IIS or Spring Boot deploy. A second product squad cannot ship. Extracting billing or entitlements gives that squad an API boundary.
Identity buried in controllers
Session checks are copied across admin and partner portals. An identity service plus strangler rules on login lets product work continue on the old branch.
.NET Framework estates
Upgrade Assistant can move project files. It does not split a shared SQL Server schema. We pair a framework move with one extracted module so the upgrade has a boundary.
Java Spring cores
Order capture and fulfillment share tables and a nightly batch. Read traffic can move first. Write cutover waits on a reconciliation report finance will sign.
Teams after a stalled rewrite
A parallel repository fell behind feature parity. Strangler routing puts a thin production path in front of customers while the monolith remains the system of record.
Typical Project Scenarios
Six situations from US discovery calls. Each is scoped as one slice after the Modernization Release Gate, not as a multi-year microservices program.
Publish dealer or partner APIs from a .NET monolith
Contract lookup, document status, and invoice PDFs sit behind internal screens. Partners need REST and webhooks. We extract the read model, version the contract, and leave admin edits on the monolith until write parity tests pass.
Split a Java order core along read and write
Checkout and fulfillment share rows and a batch that posts at 2 a.m. Eastern. Read endpoints move behind the gateway first. Writes stay on the monolith until a reconciliation job stays quiet for an agreed sample period.
Move operational reports off the OLTP database
Dashboards query production tables and stall releases. A read API or replica-backed service takes dashboard traffic slice by slice. Schema ownership is written down per context before the second consumer arrives.
Extract login without freezing the roadmap
Every controller checks a homegrown session. We stand up an identity boundary, integrate OIDC where the product already has an IdP, and route login through strangler rules. Feature squads keep merging to the monolith branch.
Sequence code boundaries with a hosting move
Leadership wants Azure or AWS in the same fiscal year. We keep strangler milestones as the product schedule and align cutover windows with cloud migration services so a DNS flip does not land on an unstable API.
Put a regression gate on a money path
Two code paths can create an invoice during the overlap. Contract tests and a small synthetic check block route promotion when totals diverge. Larger suites can move to QA automation services after the first slice.
How Delivery Works
Five phases over sixteen to twenty-four weeks for one production capability, API contracts, routing, and paired handoff. That range sits inside the published project duration of one to six months. Discovery itself follows the site pattern: a few days to align, team assembly in the following week, and first written artifacts in weeks three and four.
Discovery. Weeks 1 and 2 run the Modernization Release Gate in the hero diagram. The output is a seam list, a named first consumer, and a named on-call owner. If any check fails, we write the missing answer before opening a service repo.
Contracts. Weeks 3 to 6 produce the OpenAPI draft, versioning rules, and the anti-corruption boundary. Security reviews start here when partners will hold sandbox keys.
Pilot extraction. Weeks 7 to 12 implement the service behind a flag in staging, with contract tests and a dual-write or read-replica plan. Finance or operations reviews sample records before any production flag flips.
Production routing. Weeks 13 to 18 shift a bounded caller set. The gateway change, synthetic check, and rollback flag are reviewed by the client owner. The monolith remains system of record until write criteria pass.
Handoff. Weeks 19 to 24 are paired. Your engineers ship the next small change under review. Runbooks cover the following slice, schema ownership, and how to revert a route. After that, the same people can continue as a dedicated development team or the work can close as project-based outsourcing.
Sprints stay on the company cadence: two weeks, a demo, and a retro. The Miami account lead joins the demo when a route decision needs a buyer in the room.
Team Composition
A first slice is usually four engineers plus a Miami account lead and a part-time owner from your side. The modernization lead and the senior .NET or Java engineer are the roles that decide whether rollback works. Cutting them to lower a quote is how dual-write drift becomes a weekend incident.
The API engineer is heavier in the contract weeks and lighter once the spec is stable. QA owns contract tests and the regression samples on the money or contract path. Your product owner signs the seam list and the production route. If you only need one senior inside an existing squad, use full-stack staff augmentation or a .NET or Java delivery engagement instead of a full slice team.
Project, dedicated team, or staff augmentation, depending on how many slices you want this squad to own.
Pricing and Engagement Models
Figures below sit inside the published company bands: projects USD 15,000 to 120,000, dedicated teams USD 12,000 to 60,000 per month, staff augmentation USD 4,000 to 9,000 per month per developer. Modernization uses the upper part of those bands because the first slice includes discovery, dual-path testing, and regression. Multi-year extraction continues as a dedicated team rather than an oversized fixed bid.
Project-based
One slice: release gate, one capability, production routing, OpenAPI, regression samples, and handoff. Sixteen to twenty-four weeks. USD 45,000 to USD 120,000 after discovery, driven by schema coupling and whether partner certification is in scope.
Dedicated team
The same squad keeps extracting slices, extending APIs, and owning routing changes. USD 24,000 to USD 52,000 per month for four to six people. Thirty days notice to scale down, same as other dedicated engagements.
Staff augmentation
One or two seniors inside your squad when architecture is already yours. USD 6,000 to USD 9,000 per month per engineer, top of the published staff-augmentation band. Two-week satisfaction guarantee applies.
Compared With In-House Hiring, Freelancers, and Agencies
Outsource a slice when
- You need one production route in a quarter, and hiring a modernization-experienced .NET or Java lead will take longer than that.
- Your product team knows the domain and needs help with strangler rules, dual-write checks, and OpenAPI governance.
- Procurement wants a written release gate before an enterprise review of monolith risk.
- A previous rewrite repository stalled and you want the next milestone to be live traffic, not another branch.
Keep it in-house when
- A platform group already runs domain mapping and only needs a short spike on one endpoint.
- The estate is a handful of stateless services with separate databases.
- A vendor playbook requires a single cutover you cannot roll back per route.
Freelancers can open a service repository quickly. They rarely stay through production routing, reconciliation, and the paired weeks when your team takes the pager. A large consultancy can staff a program. Ask whether the people who wrote the seam list are the people who merge the gateway change. Miami coordination plus Latin America engineering is how we staff that overlap for US buyers. See case studies and the nearshore development model for how delivery is organized. The English page on our Argentina site covers the same service from a Cordoba delivery angle: application modernization from Argentina.
Illustrative Scenario: Whitford Equipment Finance
Composite example for evaluation. Not a published client. No outcome metrics are claimed.
The situation
Whitford Equipment Finance is a fictional US lessor. Dealers originate contracts in a .NET Framework application on IIS and SQL Server. Residual schedules, invoice PDFs, and a nightly dunning job share tables with the internal credit screen. A dealer portal vendor has asked for a read API and webhooks. The VP Engineering in Chicago has one release train and a board question about whether a rewrite is required before the portal contract starts.
Nobody has listed which stored procedures touch money versus which serve the credit UI. The platform lead wants a gateway rule for dealer reads, the monolith left in place for credit decisions, and a named on-call owner before any external key is issued.
What the slice would include
A project inside the sixteen-to-twenty-four-week window. Miami runs scope with the Chicago lead. The engineering squad is a modernization lead, a senior .NET engineer, an API engineer during contract weeks, and a QA engineer.
- Release gate: contract-read is the first module, shared Contract and Invoice tables are the seam, the dealer portal is the first consumer, and Whitford's platform lead owns the pager.
- OpenAPI for contract status, document links, and webhook delivery, with contract tests in the existing pipeline.
- A read service behind an anti-corruption layer. Writes and dunning stay on the monolith. A reconciliation query compares portal totals to invoice rows.
- Gateway canary for one dealer group, rollback flag, and a runbook for slice two if credit decisions ever move.
The point of the example is the sequence: dealer reads go live, credit workflow stays on the monolith, and the company can judge the next slice from a production route.
Risks and How They Are Reduced
A hidden join blocks the extract. A report or batch locks the table the new service needs. The seam list in weeks 1 and 2 is supposed to find that. The pilot fails in staging if it does not.
Two writers disagree. Portal totals and monolith invoices diverge. Mitigation is a reconciliation job, a threshold the client sets, and a hold on write cutover until a sample period is clean.
The gateway sends callers to the wrong backend. Auth scopes and rate limits are reviewed with the route change. A synthetic check runs per route. The rollback flag is rehearsed before the canary.
Partner contracts drift. Fields rename without a version. OpenAPI stays the source of truth, contract tests run in CI, and deprecation dates are agreed with the partner-facing owner.
The pager hits the wrong team. The release gate names the US owner. Runbooks live in the service repo. Paired weeks are the practice period before advisory hours.
Hosting dates override the code schedule. When a data-center exit is in the same year, strangler milestones stay the product clock and cloud migration aligns windows to API stability. Platform engineering and DevOps engineering pick up portals and pipelines after the boundary exists.
Questions US buyers ask before discovery
Frequently Asked Questions
A first slice delivers a signed Modernization Release Gate, a seam map of tables and jobs that block independent deploys, one extracted service or module behind an anti-corruption layer, an OpenAPI contract with CI tests, strangler routing for a bounded set of callers, a reconciliation job when both code paths write, and runbooks your US engineering owner can extend. The monolith keeps shipping product features during the slice. Hosting moves, if you need them, stay on a separate cloud migration track so code boundaries and landing zones do not fight for the same calendar.
Most first slices are .NET Framework or .NET on IIS with SQL Server, Java Spring services with shared schemas, or mixed PHP and Node admin tiers sitting in front of those cores. We use strangler fig routing, anti-corruption layers, and outbox or read-model patterns where they reduce coupling. Reference points are Martin Fowler's strangler fig description, the .NET Upgrade Assistant for framework moves, and OpenAPI 3.1 for partner contracts. Public HTTP surfaces pair with our API development practice. If the estate must also leave a data center, we sequence that work with cloud migration services.
The Modernization Release Gate asks four questions: whether one module can ship without redeploying the monolith, which tables and jobs block that deploy, which consumers will call the new API first, and which US engineer owns the pager when the new route and the monolith disagree. We pick the smallest capability that has a named consumer and a writable seam. Reporting cubes and cross-cutting auth usually wait until billing, orders, or identity has a stable contract. If the gate answers are missing, we spend the discovery weeks writing them before opening a service repository.
A first production slice with discovery, one extracted capability, strangler routing, contract tests, and paired handoff usually lands in sixteen to twenty-four weeks. That sits inside the published one-to-six-month project window. Weeks 1 to 2 cover the release gate. Weeks 3 to 6 cover API contracts. Weeks 7 to 12 cover a staging extraction. Weeks 13 to 18 cover production routing. Weeks 19 to 24 cover handoff. Shared databases, partner certification, or a compliance review on external APIs stretch the later weeks.
A bounded first slice typically lands between USD 45,000 and USD 120,000, the upper half of the published project band, because discovery, dual-path testing, and regression suites take more calendar time than a greenfield feature. Dedicated squads for ongoing extraction run USD 24,000 to USD 52,000 per month inside the published dedicated-team band. Senior staff augmentation sits at USD 6,000 to USD 9,000 per month per engineer, the top of the published staff-augmentation band, via hire full-stack developers or a .NET or Java specialist. We confirm a number after the release gate, not from a slide.
You do. Service repositories, OpenAPI files, gateway rules, feature flags, reconciliation jobs, and CI suites land in your org. Paired weeks are how the US engineering owner practices rollback before we drop to advisory hours. Ongoing pipeline and cluster work is a separate DevOps engineering engagement. Internal developer portals after the service boundaries exist are platform engineering. We do not retain production credentials after handoff.
Account coordination, procurement, and executive reviews run from Miami at 1110 Brickell Ave, with Eastern and Central overlap. Engineering is delivered from Latin America on the same business-day window. Modernization needs same-day decisions when a strangler flag misroutes a partner, a dual-write job drifts, or a .NET hotfix has to land before US close. The 2-week satisfaction guarantee and 30-day notice to scale down apply to dedicated and staff-augmentation shapes the same way they do on other Siblings engagements.
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