backend integration tests
PostgreSQL and Kafka Testcontainers
Evidence item 1Financial transaction event platform · Java flagship
Mercator
Relay
A financial-transaction event platform that makes idempotency, delivery state and controlled failure visible—from HTTP intake to Kafka and the audit ledger.
Java 21Spring Boot 4.1Kafka 4.3Angular 22Terraform 1.15
Angular tests
selection, filtering and local command state
Evidence item 2browser checks
desktop/mobile flow, overflow and axe
Evidence item 3Terraform contracts
mocked provider; no AWS account
Evidence item 4The engineering decision
Prove the failure path before adding scale.
The first slice stays in one modular deployable. Package boundaries are explicit, while independent services wait for a real deployment or scaling reason.
- 01Accept
Validate the envelope and bind an idempotency key.
- 02Commit
Write the event, audit entry and outbox intent atomically.
- 03Publish
Claim pending outbox rows and route them through Kafka.
- 04Deliver
Dedupe per destination or exhaust into the dead-letter path.
Stack selected from employer evidence
Learning breadth with a reason.
The stack responds to recurring Java, messaging, Angular, cloud and infrastructure-as-code signals in current target-employer material. It is not a collection of tools added only for novelty.
01
Java 21 + Spring Boot 4.1
Enterprise Java depth separate from the .NET flagship.
02
PostgreSQL + Flyway
Database constraints carry idempotency, audit and delivery history.
03
Kafka 4.3.1
At-least-once routing, bounded retries and a visible dead-letter path.
04
Angular 22 + signals
A second frontend ecosystem with strict TypeScript and browser evidence.
05
Terraform + AWS contract
Private ECS, encrypted RDS and IAM-authenticated MSK, tested without apply.
Atomic persistence
Event, audit and outbox intent commit together.
Observable routing
Publish, retry and dead-letter transitions remain inspectable.
Real dependencies
Testcontainers exercises PostgreSQL and Kafka, not substitutes.
Cloud contract
Terraform is mocked and tested; a paid deployment is not implied.
Verified locally; bounded honestly.
Docker health, one complete delivery route, Prometheus, tests and browser behaviour were checked locally. The AWS design has not been applied, and the Angular replay control does not claim a backend command that does not exist.
Docker route reached DELIVERED
No serious/critical axe findings
npm audit reported 0 vulnerabilities
Terraform provider mocks only
Discuss the build View Lumen Observatory
Local repository and `noindex`; not presented as a deployed production system.