Add dependency graph module and outage investigation

[devin-ai-integration]

Summary

Adds a new dependency-graph Maven module that parses the bank platform's infrastructure configuration into a typed dependency graph, and uses it to investigate a simulated outage scenario.

Graph module (dependency-graph/):

• Model: Node (typed: SERVICE, DATABASE, MESSAGE_BROKER), Edge (typed: HTTP, JDBC, AMQP, EUREKA), and DependencyGraph with BFS-based path tracing and blast radius computation.
• Parsers:
  • DockerComposeParser — extracts services, depends_on edges, JDBC/AMQP connections from environment variables, and classifies nodes by image/name keywords.
  • EurekaConfigParser — parses application.properties and application.yml for Eureka registration metadata and creates EUREKA-typed edges.
  • GatewayRouteParser — parses Spring Cloud Gateway routes (explicit lb:// routes and discovery-first routing) into HTTP edges.
  • DependencyGraphBuilder — orchestrates all parsers from a project root directory.
• Analysis: OutageAnalyzer traces dependency chains, computes transitive blast radius, gathers evidence, and generates markdown investigation reports.

Tests (35 total, all passing):

• DockerComposeParserTest (9 tests) — valid compose, broker/DB classification, JDBC edge extraction, malformed/empty inputs.
• EurekaConfigParserTest (9 tests) — properties and YAML parsing, register/no-register behavior, missing app name.
• GatewayRouteParserTest (7 tests) — discovery-first routing, explicit routes with predicate paths, malformed/empty configs.
• DependencyGraphBuilderTest (3 tests) — combined source building, null gateway handling, mixed edge types.
• OutageAnalyzerTest (7 tests) — dependency chain tracing, blast radius computation, evidence gathering, disconnected nodes, markdown report generation.

Outage investigation (OUTAGE-INVESTIGATION.md):

• Traces notification-service → discovery-service dependency chain via EUREKA registration and Docker Compose depends_on.
• Identifies blast radius: all 5 downstream services affected (complete system outage).
• Root cause: single Eureka instance is a single point of failure.
• Proposes config changes: HA Eureka (peer replication), Resilience4j circuit breakers, extended lease durations, registry caching, health-check-based depends_on.

Review & Testing Checklist for Human

• Verify the dependency graph accurately represents the bank platform topology by comparing with docker-compose.yml and service application.properties files
• Review OUTAGE-INVESTIGATION.md resilience recommendations for applicability to your deployment environment (e.g., whether HA Eureka with peer replication is feasible)
• Run mvn test -pl dependency-graph to confirm all 35 tests pass locally
• Consider whether additional edge types should be modeled (e.g., Axon Server connections from account-service)

Recommended test plan: Run mvn clean test -pl dependency-graph and verify 35/35 tests pass. Review the outage investigation document against your understanding of the system's actual runtime behavior.

Notes

• The module has no runtime dependencies beyond SnakeYAML (already provided by Spring Boot parent). Test dependencies use spring-boot-starter-test for JUnit 5.
• The DependencyGraphBuilder.buildFromProjectRoot() method can be used to generate a live graph from the actual repo on disk.
• The Docker Compose parser infers JDBC connections from MYSQL_HOST/MYSQL_DATABASE env vars in addition to parsing jdbc: URLs directly.

Link to Devin session: https://app.devin.ai/sessions/bf1182d4e6644e51ad40772ea5704e80
Requested by: @achalc

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