We are sharing a specialised consulting opportunity for experienced Software Engineers with deep expertise in legacy codebase migration, large-scale systems modernisation, and complex production-grade software environments.
This opportunity is designed for engineers who have personally executed substantial migrations across mature, mission-critical systems. The work involves designing, implementing, reviewing, and evaluating complex modernisation tasks while preserving functionality, compatibility, data integrity, security, performance, and production reliability.
Key Responsibilities
Legacy Codebase Migration & Modernisation
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Design, implement, review, and evaluate complex codebase migration and modernisation tasks
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Analyse mature production systems to determine safe and technically sound migration approaches
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Review legacy application architecture, dependencies, APIs, databases, build systems, and infrastructure
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Identify technical debt, compatibility constraints, migration risks, and hidden dependencies
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Develop migration strategies appropriate for large, interconnected production environments
Language & Runtime Modernisation
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Evaluate migrations involving major language or runtime upgrades
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Work with scenarios such as Java 8 Java 17/21, legacy .NET modern .NET, Python 2 Python 3, and PHP 7 PHP 8
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Review language rewrites such as COBOL Java/Python and JavaScript TypeScript
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Assess behavioural equivalence and compatibility across legacy and modern implementations
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Identify regressions introduced through language, runtime, or compiler changes
Framework & Application Migration
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Review major upgrades or replacements involving frameworks such as Angular, Rails, Django, Spring/Spring Boot, ASP.NET, Next.js, and Astro
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Assess architectural implications of replacing or substantially upgrading mature application frameworks
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Evaluate dependency compatibility and integration risks
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Review implementation approaches for maintainability and production readiness
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Identify subtle behavioural differences introduced during framework migrations
Database & Data-Layer Modernisation
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Evaluate migrations such as Oracle/MySQL PostgreSQL and SQL NoSQL
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Review ORM and data-access transitions including Hibernate jOOQ, Sequelize Prisma, and raw SQL ORM
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Assess data integrity, schema compatibility, migration sequencing, and application dependencies
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Identify risks involving data loss, behavioural changes, transaction semantics, and performance
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Review validation approaches for complex production data migrations
Infrastructure & Cloud Modernisation
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Review transitions from VMs or bare metal to containerised and cloud-native architectures
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Evaluate migrations involving Docker, Kubernetes, and modern infrastructure patterns
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Assess deployment architecture, operational dependencies, scalability, and production resilience
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Review staged rollout and rollback strategies
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Evaluate whether infrastructure changes preserve reliability and operational visibility
CI/CD & Build Tooling
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Review modernisation of deployment pipelines such as Jenkins/Travis GitHub Actions or GitLab CI
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Evaluate build and package-tool migrations including Maven Gradle, Webpack Vite, CRA Next.js, and npm pnpm
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Assess build reproducibility, dependency management, deployment safety, and automation quality
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Identify migration risks within mature CI/CD environments
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Review changes for maintainability and operational effectiveness
API & Integration Migration
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Evaluate transitions such as REST GraphQL, HTTP/REST gRPC, and SOAP or legacy APIs modern interfaces
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Assess backward compatibility and downstream integration impact
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Review API contracts, dependency changes, and migration sequencing
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Identify compatibility risks and behavioural differences
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Evaluate strategies for maintaining continuity during interface transitions
Authentication & Identity Modernisation
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Review migrations from legacy authentication systems to OAuth/OIDC, SAML/SSO, and modern identity platforms
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Assess security, compatibility, authorisation, and integration implications
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Identify authentication or access-control regressions
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Review migration sequencing and transition strategies
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Evaluate implementation quality and production readiness
Repository, Dependency & Toolchain Migration
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Evaluate polyrepo monorepo transitions using tools such as Bazel, Nx, or Turborepo
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Review replacement of deprecated or end-of-life libraries, APIs, runtimes, and vendor SDKs
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Assess dependency graphs and compatibility across large software ecosystems
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Identify upgrade risks created by transitive dependencies or legacy integrations
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Evaluate migration strategies for maintainability and long-term sustainability
Testing, Validation & Production Safety
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Develop and review testing strategies for complex migrations
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Evaluate unit, integration, browser, and end-to-end testing migrations
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Identify migration regressions and behavioural differences
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Assess compatibility, observability, staged rollout, and rollback strategies
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Evaluate whether proposed migration solutions are sufficiently validated for production use
Technical Evaluation
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Review migration solutions for correctness, completeness, maintainability, and production readiness
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Analyse unfamiliar codebases and diagnose subtle migration failures
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Evaluate proposed technical decisions against realistic enterprise constraints
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Identify missing dependencies, edge cases, regression risks, and unsafe assumptions
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Provide clear, technically rigorous feedback on migration approaches and implementations
Ideal Profile
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5+ years of professional software engineering experience, ideally at Senior, Staff, Principal, Lead, or equivalent level
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Significant hands-on experience executing large-scale production migrations
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Personally owned or made substantial technical contributions to complex modernisation initiatives
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Strong experience working with mature systems involving technical debt, complex dependencies, legacy integrations, and significant regression risk
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Strong knowledge of compatibility, testing, observability, staged rollouts, rollback strategies, and behavioural equivalence
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Ability to reason deeply about unfamiliar codebases and diagnose subtle migration failures
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Experience with one or more major migration categories including languages, frameworks, databases, APIs, infrastructure, CI/CD, authentication, repositories, testing, or dependencies
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Particularly valuable experience modernising systems within financial services, fintech/payments, trading, insurance, healthcare, telecom, large technology companies, or other high-reliability environments
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For mainframe modernisation work, experience with COBOL, z/OS, CICS, JCL, DB2, VSAM, batch processing, and COBOL-to-Java/Python migration is particularly valuable
Engagement Details
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Independent contractor engagement
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Fully remote
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Flexible scheduling based on project requirements
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Talent-network opportunity with potential for ongoing project work
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Work focuses on technically challenging migration problems modelled after large-scale production systems
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Projects may be extended, shortened, or concluded based on project needs and performance
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Work must be completed without using confidential or proprietary information belonging to any employer, client, institution, or other third party
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H1-B and STEM OPT support is unavailable for this engagement
About the Platform
This opportunity is available through 24-MAG LLC. We connect experienced professionals with remote consulting opportunities across technical, evaluation, and project-based workstreams.
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