[BE-49] Structured logging with Pino

[yusuftomilola]

Overview

The platform uses NestJS's default console logger which outputs unstructured text. In production this is unqueryable by log aggregators (Datadog, CloudWatch, Papertrail). Structured JSON logging with Pino gives every log entry a consistent schema with correlation IDs for request tracing.

Context

• backend/src/main.ts — where app.useLogger() is configured
• NestJS supports custom loggers via LoggerModule from nestjs-pino
• pino-http middleware provides HTTP request/response logs

Tasks

• Install packages: npm install nestjs-pino pino-http pino-pretty
• In backend/src/app.module.ts: add LoggerModule.forRoot({ pinoHttp: { ... } }) from nestjs-pino
• Log format configuration:
  • NODE_ENV=production: plain JSON (no pino-pretty)
  • NODE_ENV=development: human-readable via pino-pretty (transport: { target: 'pino-pretty' })
• Each log entry includes: timestamp (ISO 8601), level, context (NestJS module/class name), msg, reqId (auto-generated UUID per request via genReqId)
• HTTP request/response logs via pino-http: log method, url, statusCode, responseTime on every response
• Redact sensitive fields using Pino's redact option: ['req.headers.authorization', '*.password', '*.totpSecret', '*.smsOtpCode']
• In backend/src/main.ts: call app.useLogger(app.get(Logger)) from nestjs-pino to replace NestJS default logger

Files to Modify / Create

• backend/src/main.ts
• backend/src/app.module.ts