Senior Java Engineer – Application / Database Modernization (Freelancer)

Mactores is the agent-native AWS modernization firm. Most modernization work doesn't ship, it stalls in pilots, slips a year, or lands at three times the budget. We exist to ship it: production systems running, legacy retired, outcomes measured. Our delivery is built on Aedeon, the agent platform built by Mactores' founders' sister company, which absorbs the repetitive 60–70% of engagement work, discovery, dependency mapping, validation, test generation, that traditional consulting bills human hours against. Forward-deployed engineers own the rest: architecture, judgment, and cutover, on dates we commit to in the contract.

What you will do?

• Decompose a large Java monolith into microservices: identify bounded contexts, extract services with the strangler-fig pattern, and define REST and event contracts.
• Apply proven microservice patterns: database-per-service (staged pragmatically), Saga with compensating actions, transactional outbox, idempotent consumers, and resilience patterns such as circuit breakers.
• Remediate Oracle- and SQL Server-specific code for Aurora PostgreSQL: rewrite embedded SQL, stored procedure calls, sequences, pagination, date handling and error handling, and update JPA/Hibernate or MyBatis mappings.
• Work closely with database migration engineers so application-layer SQL lines up with the converted target schema and supports environment cloning and refresh.
• Deploy and run services on Amazon EKS: Helm charts, health probes, JVM and resource tuning, autoscaling, ALB/NLB ingress, and Pod Identity for AWS access.
• Build and maintain GitHub Actions CI/CD pipelines for Java services: Maven/Gradle builds, scanned images in Amazon ECR, Flyway/Liquibase migrations, and promotion from dev to prod with approval gates and rollback.
• Automate testing: unit, Testcontainers integration, contract, API and smoke tests, plus parity and performance tests that prove modernized services match or beat legacy baselines. Wire the client's existing suites into the pipeline.
• Use GenAI-assisted tools (Claude Code) to accelerate code conversion, and validate their output rigorously.
• Instrument services for Dynatrace and support production cutover: rehearsals, validation, rollback planning and stabilization.
• Produce engineering documentation that outlives the engagement: design notes, code-migration runbooks, troubleshooting guides and knowledge-transfer material for the client's teams.
• Pair with client engineers and SMEs across US- and India-based teams, reviewing code and keeping business logic aligned.

What are we looking for?

• Bachelor's degree in Computer Science, Engineering, or a related field.
• 5+ years of professional Java development experience (Java, Spring Boot, Spring Cloud, JDBC, JPA/Hibernate or MyBatis).
• Hands-on experience decomposing a monolith into microservices in production: domain-driven design, Saga and event-driven integration (Kafka, SQS/SNS or EventBridge).
• Strong SQL expertise. You can analyze, optimize and rewrite complex SQL embedded in Java, and you've migrated application code from Oracle or SQL Server to PostgreSQL.
• Deep understanding of JDBC, ORMs, transaction management, connection pooling and database-driven application flows.
• Production experience running Spring Boot on Kubernetes (preferably Amazon EKS) with Docker and Helm.
• CI/CD experience with GitHub Actions: reusable workflows, environment approvals and OIDC authentication to AWS.
• Test automation skills: JUnit 5, Mockito, Testcontainers, REST Assured and consumer-driven contract testing.
• Working knowledge of AWS application services: Aurora PostgreSQL, RDS Proxy, KMS and IAM roles for workloads.
• Regular use of AI coding assistants in real delivery work.
• Excellent spoken and written English, and the ability to work US Mountain Time business hours with globally distributed teams.

You will be preferred if you

Have exposure to automated code-refactoring tools or GenAI-assisted remediation workflows.
Have experience with Amazon VPC Lattice or a service mesh.
Have done performance testing (Gatling, JMeter or k6) and worked with observability stacks (Dynatrace or OpenTelemetry).
Have worked on MuleSoft integrations and Ping Identity (OAuth 2.0 / OIDC).
Have worked in SOX-regulated environments: change control, approvals and audit evidence.
Have worked on e-commerce, subscription ordering or commission/compensation systems.
Hold an AWS certification (Developer Associate or Solutions Architect) and have basic Terraform.