Deloitte Internship Presentation
Migration and Modernization of Legacy Enterprise Infrastructure to Java 21
Full Stack & Software Engineering Intern
Transformation & Technology
DURATION
6 Months
Apr – Sep 2026
HANDOFF DATE
30 September
2026
INTERN NAME
Muhammad Hafeez Bin Ilias
Full Stack Developer
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Project Description
Project Description
Problem Statement
The reliance on Java 8 presents critical operational risks, as the platform lacks security updates and performance patches. Operating as a siloed legacy system leads to excessive maintenance efforts and significant challenges when integrating with modern centralized platforms like microservices. To mitigate these risks and improve system maintainability, it is essential to migrate these core modules into a centralized environment that supports modern standards and efficient resource management. A thorough analysis is required to ensure that all business requirements and validation rules are accurately preserved during the migration to prevent inconsistencies that could affect data integrity.
Scope
Analyze the existing legacy backend services to understand the technical debt, core business logic, and communication protocols.
Refactor existing services to resolve architectural rigidities and optimize performance through Java 21 features.
Integrate microservices into the unified service architecture via updated API configurations.
Establish robust security protocols and modern communication standards to ensure long-term scalability.
Conduct functional testing to ensure parity between legacy behavior and the modernized system.
Key Objectives
Objective 1
To analyze the existing legacy infrastructure functionality, core services, and business requirements to ensure a seamless transition from Java 8 to Java 21.
Objective 2
To configure and implement the modernized backend within the Java 21 framework using the "lift and shift" methodology while preserving original business functionality.
Objective 3
To perform rigorous testing and validation to ensure the migrated system meets security protocols and maintains interoperability with microservices.
Methodology
Our Approach
A Waterfall methodology was used to migrate and modernize the legacy infrastructure to Java 21 — each phase completed and signed off before the next began, ensuring stability and predictability for a mission-critical enterprise system.
Discovery & Analysis
Audited the legacy codebase, dependencies, and infrastructure to fully scope the migration before any code was touched.
Design & Planning
Locked in the upgrade roadmap, sequencing, and rollback strategy upfront — requirements and design finalized before implementation begins.
Implementation
Migrated the system to Java 21 in fixed, sequential phases — upgrading language features, dependencies, and APIs one layer at a time.
Testing & Optimization
Validated functionality and performance through regression testing, then refined the modernized system before final handoff.
Tools & Technologies
Project Timeline
Project Timeline
6-Month Internship: April – September 2026
April
Month 1
May
Month 2
June
Month 3
July
Month 4
August
Month 5
September
Month 6
Planning & Setup
Design & Architecture
Frontend Development
Backend Development
Integration & Testing
Deployment
Handoff & Documentation
Project Handoff: 30 September 2026
Development Phase
Development Phase
Core Development: 3 Months of Active Implementation
Month 1
April
Conducted a comprehensive audit of the legacy Java 8 backend, mapping core services, business logic, and inter-service communication protocols. Collaborated with stakeholders to document requirements and pinpoint the technical debt that needed to be addressed before migration.
Key Achievements
- Audited the legacy Java 8 codebase and documented core business logic across all modules
- Interviewed stakeholders to capture functional and non-functional requirements
- Identified key architectural risks and technical debt hotspots
Month 2
May
Designed the target Java 21 architecture and defined the "lift and shift" migration strategy to preserve existing business functionality while modernizing the underlying platform. Set up the development, testing, and CI/CD environments needed for implementation.
Key Achievements
- Designed the target Java 21 architecture and migration roadmap
- Established CI/CD pipelines and development/test environments
- Defined the test strategy and parity criteria for validating migrated behavior
Month 3
June
Executed the core migration of legacy services into the Java 21 framework, refactoring outdated APIs and dependencies while preserving original business behavior. Began integrating the modernized services with existing microservices via updated API configurations.
Key Achievements
- Migrated core backend services from Java 8 to Java 21
- Refactored deprecated APIs and updated outdated dependencies
- Integrated modernized services with existing microservices
Maintenance Phase
Maintenance Phase
Optimization, Maintenance & Handoff: 3 Months of Stabilization
Month 4
July
Performed rigorous functional, regression, and security testing to confirm the migrated system matched legacy behavior and met modern security standards. Worked closely with QA to resolve defects and validate data integrity across all business workflows.
Focus Areas
- →Executed functional and regression test suites across all modules
- →Validated security protocols and remediated identified vulnerabilities
- →Resolved defects surfaced during integration testing
Month 5
August
Profiled and optimized the migrated application to take advantage of Java 21 performance improvements, including virtual threads and enhanced garbage collection. Fine-tuned configurations to improve throughput and reduce latency under production-like load.
Focus Areas
- →Benchmarked and optimized application performance using Java 21 features
- →Tuned JVM and service configurations to improve throughput
- →Conducted load testing to validate scalability under peak conditions
Month 6
September
Finalized technical documentation, runbooks, and knowledge-transfer materials to support long-term maintainability. Completed final stakeholder sign-off and prepared the system for a smooth handoff to the operations team.
Focus Areas
- →Authored technical documentation and operational runbooks
- →Conducted knowledge transfer sessions with the operations team
- →Completed final validation and formal project handoff
Handoff Ready: 30 Sep
Professional Growth
Professional Growth & Deloitte Culture
Professional Growth
Technical Skills
Grew into a full stack developer — building backend services in Java (Spring Boot) and modern, responsive UIs in React while migrating legacy infrastructure to Java 21.
Collaboration
Worked closely with senior engineers across the stack, turning requirements into shipped features spanning Java APIs and React front ends.
Problem Solving
Debugged and resolved legacy Java 21 migration issues independently, tracing bugs across backend logic and React UI to working solutions.
Learning
Rapidly leveled up on enterprise Java, React patterns, and modern full stack tooling through hands-on delivery.
Deloitte Culture
Global Recognition
#1
Most valuable professional
services brand
#8
World's strongest
brands overall (2026)
With the Team
At Deloitte, we believe that our people are our greatest asset. The culture of continuous learning, collaboration, and excellence defines our organization.
Conclusion
Conclusion
End-to-End SDLC Exposure
Involved in the project from kickoff to final delivery, gaining first-hand experience with the real Software Development Life Cycle — requirements, design, implementation, testing, and handoff.
Communication & Problem-Solving
Learned how to ask the right questions, give clear status updates, and brainstorm with the team to work through technical challenges.
"More than the migration itself, this internship taught me what Deloitte lives by every day — making an impact that matters. Modernizing a legacy system isn't just a technical upgrade; it's building a stronger, more reliable foundation for the people and processes that depend on it, and that's the standard I'm carrying forward."
Thank You
Muhammad Hafeez Bin Ilias
Full Stack & Software Engineering Intern
Deloitte Transformation & Technology