MQTT GUIDE
4 min readWhat Is an MQTT Broker?
An MQTT broker is the central server that sits between MQTT clients: it receives every published message and routes it to the clients subscribed to the matching topic. The broker manages connections, subscriptions, per-QoS delivery, session state, and authentication — so publishers and subscribers never talk to each other directly.
If MQTT is the language IoT devices speak, the broker is the switchboard they all call into. It is the one component every client connects to, and it is what makes MQTT's decoupled publish/subscribe model work.
What an MQTT broker does
Clients don't send messages to each other — they send them to topics on the broker. When a message is published, the broker finds every client subscribed to a matching topic and delivers a copy to each one. A single publish can fan out to many subscribers, and a subscriber can receive from many publishers, all without any of them knowing about the others.
What the broker manages
Beyond routing, the broker owns the state and rules of the whole system:
Types of MQTT brokers
Brokers come in a few flavors, and the right one depends on how much you want to run yourself:
TBMQ is open-source, with a professional edition and a managed private-cloud option — so you can start self-hosted and move to managed hosting later without switching brokers.
What to look for in a broker
Brokers differ most in how far they scale and how they persist data. For production IoT, the questions that matter are: how many concurrent connections and how much throughput it sustains, whether it clusters horizontally, which MQTT versions it supports (such as 3.1.1 and 5.0), how it persists messages for offline clients, and what authentication and authorization it offers. For the long run, also weigh the strength of its community or commercial support and the total cost of running it.
The broker in TBMQ
TBMQ is an open-source MQTT broker built by the ThingsBoard team, supporting MQTT 3.1, 3.1.1, and 5.0 and engineered to scale to 100M+ concurrent connections on a single cluster by using Kafka as its internal backbone. The TBMQ broker guide covers what sets it apart and how its DEVICE and APPLICATION clients differ. To see how the pieces fit together, the architecture overview walks through the design, and getting started spins one up in minutes.
Frequently asked questions
Is an MQTT broker a server?
Yes. The broker is the central server in an MQTT deployment. Every client connects to it, and it is responsible for receiving published messages and forwarding them to the right subscribers.
What is the difference between an MQTT broker and an MQTT client?
A client is any device or application that publishes or subscribes; the broker is the single hub they all connect to. Clients never talk to each other directly — the broker routes every message between them.
Do I need a broker to use MQTT?
Yes. MQTT is a broker-centric publish/subscribe protocol, so a broker is required. There is no peer-to-peer mode; publishers and subscribers are decoupled through the broker.
What are examples of MQTT brokers?
There are many open-source and commercial brokers. TBMQ is an open-source MQTT broker built by ThingsBoard for very large-scale deployments.
How many devices can an MQTT broker handle?
It depends on the broker and its architecture. Lightweight single-node brokers handle thousands to hundreds of thousands of connections; clustered brokers like TBMQ are designed to scale to 100M+ concurrent connections.
Run it yourself
TBMQ is a free, open-source MQTT broker built to scale. Spin it up in minutes or try the live demo — no install required.