MQTT Load Generator

Small Java CLI tool that simulates many MQTT producers publishing JSON messages in parallel.

Each producer simulates a single MQTT device (for example, one sensor).

What it does

At runtime, the app:

1. Parses CLI arguments into a ProducerConfig.
2. Builds a payload filler string (repeated A) sized to help reach a target message size.
3. Starts a fixed thread pool with one worker per producer.
4. Connects each worker to the MQTT broker with a unique client ID.
5. Publishes messages to --topic/<producerId> using QoS 0.
6. Disconnects and closes each MQTT client after sending.

Each message is JSON and includes:

• message_id (UUID)
• timestamp (UTC, nanosecond precision format)
• temperature (random double between 86 and 88, rounded to 2 decimals)
• payload (filler string)

Requirements

• Java 17+
• Maven 3.8+ (or compatible)
• Reachable MQTT broker endpoint (for example tcp://localhost:1883)

Build

mvn clean package

This creates a runnable shaded jar in target/.

Copy the created JAR from target/ into the docker project MqttLoadGenerator folder, then build the Docker image:

docker build -t mqttloadgenerator .

Run the application container for Kafka:

docker run -it --rm --name mqttproducer /
  --network kafka-docker_kafka_network /
  mqttloadgenerator java -cp app.jar org.example.MqttLoadGenerator /
  --broker=tcp://mqtt-broker:1883 /
  --topic=mqtt/temp /
  --producer-count=250 /
  --messages-per-producer=1000 /
  --delay-between-messages=50 /
  --payload-size=512

Run the application container for Pulsar:

docker run -it --rm --name mqttproducer /
  --network pulsar-docker_pulsar_network /
  mqttloadgenerator java -cp app.jar org.example.MqttLoadGenerator /
  --broker=tcp://pulsar:1883 /
  --topic=persistent://public/default/temp /
  --producer-count=250 /
  --messages-per-producer=1000 /
  --delay-between-messages=50 /
  --payload-size=512

CLI arguments

All arguments use --name=value format.

Argument	Required	Default	Description
--broker	Yes	none	MQTT broker address. Example: tcp://localhost:1883
--topic	Yes	none	Base topic. Each producer publishes to <topic>/<producerId>
--producer-count	No	100	Number of concurrent producer workers
--messages-per-producer	No	600	Number of messages each producer sends
--delay-between-messages	No	1000	Delay in milliseconds between messages for each producer
--payload-size	No	130	Target minimum size logic input for payload filler

Validation and clamping behavior:

• Missing --broker or --topic causes startup failure with an error message.
• --producer-count and --messages-per-producer are clamped to at least 1.
• --delay-between-messages is clamped to at least 0.
• --payload-size is clamped to at least 130.

Throughput and volume math

• Total producers = producer-count
• Messages per producer = messages-per-producer
• Total messages attempted = producer-count * messages-per-producer

Approximate per-producer duration:

• random startup jitter (0-1499ms) + ((messages-per-producer - 1) * delay-between-messages)

Approximate produced messages per second (steady state, ignoring startup jitter):

• produced-messages-per-second = producer-count * (1000 / delay-between-messages)