MQTT Patterns for IoT

When to use

• Designing MQTT topic hierarchies for a new IoT system
• Choosing the right QoS level for telemetry, commands, or alerts
• Implementing device presence detection with retained messages and LWT
• Selecting or scaling an MQTT broker (Mosquitto, EMQX, HiveMQ, VerneMQ)
• Adopting MQTT 5.0 features like shared subscriptions, message expiry, or user properties
• Reviewing client library options for embedded C, Python, Node.js, Java, or Go

Core principles

1. Topic hierarchy is your ACL and filter contract — put the device ID early; flat topics destroy per-device access control and wildcard efficiency
2. QoS 1 is the sane default — deduplicate on the backend; QoS 2's four-way handshake costs more than it saves in most telemetry scenarios
3. LWT plus retained messages equals a free presence system — no polling, no heartbeat endpoint, broker handles it
4. MQTT 5.0 shared subscriptions replace every hand-rolled consumer group — load-balance backend processors without custom coordination
5. Never subscribe to # in production — you will receive everything on the broker; your consumer will not survive it

Reference Files

• references/topics-and-qos.md — topic naming conventions, hierarchy patterns, QoS comparison table, retained messages, LWT configuration for device presence
• references/brokers-and-mqtt5.md — broker selection (Mosquitto / EMQX / HiveMQ / VerneMQ), MQTT 5.0 feature guide, client libraries per language, anti-patterns to avoid