01 - Application "pont" BDD

Parc – MQTT → MySQL Bridge

A lightweight Python service that bridges a Mosquitto MQTT broker to a MySQL database for the Parc greenhouse monitoring system.

Programme génére à l'aide de ClaudeCode

Architecture

[IoT sensors / controleurs]
        │  MQTT  serre/X/bac/Y
        ▼
 ┌─────────────┐         ┌──────────────────────┐
 │  Mosquitto  │ ───────▶│  bridge.py (Python)  │ ──▶  MySQL (external)
 │  (broker)   │         │  subscribe + persist │
 └─────────────┘         └──────────────────────┘
   Docker container             Docker container

Both containers share a private Docker network (parc-net). The MySQL server is external (managed separately).

MQTT topics

Pattern	Description
`serre/<numero>/bac/<numero>`	Measurements from bac `<numero>` inside serre `<numero>`

Payload format (JSON)

{ "humiditeAmbiante": 65.3, "temperatureAmbiante": 22.1 }

Multiple sensor keys can coexist in a single payload.

Supported sensors

JSON key	`id_capteur`
`humiditeAmbiante`	1
`humiditeSol`	2
`temperatureAmbiante`	3

Error handling

All errors are persisted to the error table with one of these type_erreur values:

Code	Trigger
`BAC_NOT_FOUND`	Serre or bac number not in the database
`UNKNOWN_SENSOR`	Sensor key not in the known list
`INVALID_PAYLOAD`	JSON parse error or non-object payload
`INVALID_VALUE`	Non-numeric value for a sensor
`VALUE_OUT_OF_RANGE`	Value clamped to sensor min/max
`INVALID_ENCODING`	Non-UTF-8 payload
`MQTT_DISCONNECT`	Unexpected broker disconnection
`DB_ERROR`	Transient database query failure
`DB_INSERT_ERROR`	Failed to insert a mesure row
`UNEXPECTED_ERROR`	Unhandled exception (catch-all)

When a value is out of range, the clamped value (min or max) is written to mesure and an error row is inserted.

Quick start

1. Prerequisites

Docker ≥ 24 with Compose plugin
An accessible MySQL / MariaDB server with the parc schema applied

2. Configuration

cp .env.example .env
# Edit .env and fill in DB_HOST, DB_USER, DB_PASSWORD, etc.

3. Start

docker compose up -d --build

4. Verify

# Follow bridge logs
docker compose logs -f bridge

# Test with a dummy publish
docker run --rm --network parc-net eclipse-mosquitto:2 \
  mosquitto_pub -h mosquitto -t "serre/1/bac/1" \
  -m '{"humiditeAmbiante": 65, "temperatureAmbiante": 22}'

Environment variables

Variable	Default	Description
`DB_HOST`	(required)	MySQL host
`DB_PORT`	`3306`	MySQL port
`DB_NAME`	`parc`	Database name
`DB_USER`	(required)	MySQL user
`DB_PASSWORD`	(required)	MySQL password
`MQTT_HOST`	`mosquitto`	Broker hostname
`MQTT_PORT`	`1883`	Broker port
`MQTT_KEEPALIVE`	`60`	MQTT keepalive (s)
`MQTT_USER`	(empty)	Broker username (optional)
`MQTT_PASSWORD`	(empty)	Broker password (optional)
`DB_RETRY_DELAY`	`5`	Seconds between DB retries
`MQTT_RETRY_DELAY`	`5`	Seconds between MQTT retries
`LOG_LEVEL`	`INFO`	`DEBUG`/`INFO`/`WARNING`/`ERROR`

File layout

.
└── mqtt-bridge
    ├── bridge.py
    ├── docker-compose.yml
    ├── Dockerfile
    ├── mosquitto
    │   ├── client-certs
    │   │   ├── client.crt
    │   │   ├── client.csr
    │   │   └── client.key
    │   ├── clients-certs.sh
    │   ├── config
    │   │   ├── mosquitto.conf
    │   │   └── mosquitto.conf.bak
    │   ├── server-certs
    │   │   ├── ca.crt
    │   │   ├── ca.key
    │   │   ├── ca.srl
    │   │   ├── server.crt
    │   │   ├── server.csr
    │   │   └── server.key
    │   ├── server-certs.sh
    │   └── v3.ext
    ├── README.md
    └── requirements.txt