Mosquitto Performance on low-end VM

I am currently designing a new topology for inter-controller communication using Mosquitto as broker. For fun, I wanted to see how much I could push Mosquitto so I started a low-end Ubuntu VM in Azure and wrote a simple .NET Test application using MQTTnet to put a bit of a load onto it.

I choose the B1s VM (1 vcpu and 1 GiB of memory), installed Ubuntu, installed Mosquitto and opened the default 1883 port for MQTT. This would serve as my broker.

For the benchmarking application I wrote a .NET Core Console app that would:

• Instantiate N Tasks
• Each Task instantiates its own MQTT Net client and Connect to the broker.
• Each Task subscribes to to a “ping/{clientid}” topic and each second send a ping message containing Environment.TickCount + a 65K payload to the ping topic with its own client id.
• The ping would be returned back to the Task due to the subscribe and ping-time could be measured.

With N = 200, 200/msg/s would be transmitted to the broker and back again, resulting in a theoretical bandwidth requirement of 13MB/s + overhead.

For the benchmark I decided to run the client on my own dev machine, since I can currently upload 50MB/s using the fiber connection that I have available - plenty of bandwidth for my test purposes.

Starting the client app with N=200, I saw the ping times fluctuating from 60ms to 300ms, indicating a bottleneck somewhere (needs to be analyzed further before concluding anything)

Using Azure Metrics, I could quickly mesure the CPU and bandwidth usage of the VM. The CPU usage of the VM peaked at 28.74% and the upload from the VM to my Client peaked at 15.61 MB/s or 125 Mbit/s.

I did not expect this kind of bandwidth / performance from this class of VM in Azure. I of course only tested the burst performance and not the long running performance of the VM, which might differ due to the VM class being a ‘burstable VM’.

Conclusion after this test: if you want a MQTT broker, start with a small burstable VM and see how it performs over time and then upgrade.