This is WIP.

rumsim: A data generator for simulation and benchmarking IoT workloads.

Quickstart

For scalable workload generation, please see the associated Kubernetes operator.

You can directly run the simulator by setting a bunch of environment variables.

Broker-related variables

Variable	Default	Description
BROKER_URL	mqtt://localhost:1883	The MQTT broker to send data to.
BROKER_USER	mqtt	The username for connecting to the broker.
BROKER_PASS	pass	The password for connecting to the broker.
BROKER_CLIENT_ID	rumsim-0	The client ID for connecting to the broker.
BROKER_QOS	1	The quality of service (0..2) used for MQTT messages.

Simulation-related variables

Variable	Default	Description
SIM_DEVICES	100	The number of devices to simulate.
SIM_DATA_POINTS	100	The number of data points per devices to simulate.
SIM_SEED	0	The random number seed for generating data.
SIM_FREQUENCY_SECS	1	How often the data should be generated.
SIM_START_TIME	<immediate>	ISO datetime when the simulator starts generating.
SIM_RUNS	usize::MAX	Number of simulator runs.

Observability-related variables

Variable	Default	Description
OTLP_ENDPOINT	<console>	URL of OTLP collector for traces and metrics.
OTLP_AUTH	<unset>	Authentication string for OTLP collector.

Other configuration

Variable	Default	Description
CAPACITY	1000	Capacity of message buffer.
RUST_LOG	info	OTLP trace level.

Trace levels are:

• trace: Individual data points that are generated.
• debug: Start and stop of individual simulation runs.
• info: Start and stop of simulation.
• error: Error messages.

Build and run the device simulator

cargo build -r
# Start your MQTT broker.
# Set environment variables (or try the defaults).
target/release/rumsim

Message format

Data is sent in Cumulocity IoT SmartREST 2.0 format.

Topic:

s/us/{BROKER_CLIENT_ID}\_{device ID}

Payload:

201,S,<time>,SF,<datapoint 1>,<value 1>,,SF,<datapoint 2>,<value 2>,…

Notes:

• BROKER_CLIENT_ID should be different for each instance of the simulator. Using the Kubernetes operator, the BROKER_CLIENT_ID is the ID of the pod (name of the simulation plus a running number).
• The device ID is a running number.

Known issues

The simulator currently just crashes if you send so many data points that the maximum packet size of the MQTT broker is exceeded:

2024-04-02T15:09:50.377381Z WARN rumsim: Failed to connect error=MqttState(OutgoingPacketTooLarge { pkt_size: 18136, max: 10240 })

However, the last messages are apparently not correctly forwarded to the OTLP endpoint for some reason (even though I call the shutdown method), so you currently do not see why the simulator crashed.

Notes/ideas

• Add some unit tests to main with mockall.
• Try passing opentelemetry span IDs through MQTT 5? Is it possible to have an MQTT 3 fallback for servers not supporting mqtt 5?
• Make OpenTelemetry and Tonic dependencies optional, put observability into an optional module and have a feature flag to compile OTLP support in or not. It looks like the whole observability stack adds 5 MB to the final binary?