Senior Java Engineer – Application / Database Modernization (Freelancer)

Job description

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. Enterprises stuck on Oracle carry license renewals, vendor-specific SQL nobody wants to touch, and application layers welded to the database underneath them. This role sits in our Application & Database Modernization pillar: you'll work an Oracle-to-PostgreSQL migration where Aedeon handles the mechanical conversion at scale and you own what the tools can't, which is the refactoring judgment inside large enterprise Java codebases. You'll rewrite the SQL the application actually depends on, align it with the modernized schema, prove functional parity, and see the application through production cutover. Not a proof of concept. A system that ships. ### 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.