Unified logging behaviour

- Logger doesn't start with log level DEBUG by default, instead reads a environment variable
- Added extensive debug logging
- Wrote a readme
- Changed database healthcheck loop to only catch pymsql errors

README.md

@@ -1,2 +1,38 @@
-# backend-push-notifications
+# Backend Push Notifications
 
+
+## Overview
+This part of the backend handles device push notifications for registered users. It consumes messages from RabbitMQ, looks up user device tokens from a MySQL database, and sends notifications via Expo's API. Failed deliveries are retried or sent to a dead-letter queue.
+
+
+## Requirements
+- Python 3.12+
+- MySQL database
+- RabbitMQ
+- Python packages from requirements.txt
+
+
+## Configuration
+
+**Environment variables:**
+
+- `LOG_LEVEL` (DEBUG, INFO, WARNING, ERROR, CRITICAL)
+
+- `RABBITMQ_URL`
+
+- `MYSQL_HOST`, `MYSQL_USER`, `MYSQL_PASSWORD`, `MYSQL_DATABASE`
+
+- `API_ENDPOINT` (Expo push API)
+
+
+## Metrics
+
+Metrics are exposed on port `9000` for Prometheus, including:
+
+- `MSG_PUBLISHED`
+
+- `MSG_FAILED`
+
+- `MSG_RETRY`
+
+- Queue sizes