Haskell Type-Safe API Contract Monitor

Project Description

A web-based Haskell application that monitors API endpoints and validates their responses against user-defined contracts. It ensures API reliability by detecting contract drift, slow responses, unexpected statuses, and more.

Features

• JSON contract validation (types, required/optional fields, strict matching)
• Uptime and latency monitoring
• HTTP checks targeting owned APIs
• Prevents internal probing via SSRF mitigation
• PostgreSQL backed

Stack

• Haskell
• Servant & Lucid (Web Layer)
• Aeson (JSON parsing)
• PostgreSQL (Database)

Folder Structure

• app/: Contains Main.hs
• src/: Core logic (Types, Server, Checking, DB)
• test/: Tests (Hspec + QuickCheck)
• public/: Assets (CSS, JS)
• templates/: HTML templates
• scripts/: Helper scripts for deployment and building
• logs/, data/: App logs and stored samples

Environment Variables

The application uses a .env file for configuration. Do not commit .env. See .env.example or look at .env for placeholders.

Security

This tool restricts monitoring of local or private IP addresses unless ALLOW_PRIVATE_TARGETS is set to true in .env.

How to Build and Run

• Tests: cabal test
• Build: cabal build
• Run locally: cabal run api-contract-monitor

Deployment

• Deployment is on a VPS with Systemd and Nginx.
• Target URL: https://haskell.micutu.com
• Important: The owner handles git commit and push manually.

Database

Uses PostgreSQL. Update the DATABASE_URL in .env accordingly.

Troubleshooting

• If port is occupied, the deployment script scans for an available port and updates .env.
• Database connection failure: check PostgreSQL is running.
• Nginx 502: The Haskell server might be down or binding to the wrong port.