MQTT Interview Questions and Answers

This page covers top MQTT interview questions and answers to help interviewees pass job interviews for MQTT engineer positions. These MQTT questions are written by specialists in the MQTT domain.

Q&A

Question -1: What is MQTT?

Answer -1: MQTT is a broker-based protocol where client devices communicate via a broker. The broker is a server that can be installed on any machine, including in the cloud. It’s a lightweight message queueing and transport protocol based on a publish/subscribe architecture.

Question -2: Mention applications or use cases of the MQTT protocol.

Answer -2: It’s used for numerous applications such as M2M (Machine-to-Machine), IoT (Internet of Things), WSN (Wireless Sensor Networks), telemetry, and more.

Question -3: Does MQTT use TCP or UDP?

Answer -3: MQTT uses TCP/IP.

Question -4: Which port number is used by MQTT?

Answer -4: It uses port number 1883.

Question -5: Does MQTT support Security?

Answer -5: Yes, it uses SSL/TLS for security. It encrypts the payload, making it payload agnostic.

Question -6: What is an MQTT topic?

Answer -6: Communication between the sender (publisher) and receiver (subscribers) in MQTT is based on messages called “topics.”

In MQTT, a topic is a UTF-8 string. To receive messages, clients must subscribe to a particular topic (e.g., temperature sensor data). Each topic can have one or more levels, which are separated by a slash (called a topic separator).

Question -7: Explain the MQTT broker architecture with a use case example.

Answer -7: Imagine client #2 updates the temperature with the broker. Client #1 wants to know the updated temperature from the broker. Here, client #2 acts as the publisher, and client #1 acts as the subscriber.

The following figure illustrates the message flow between client #1 and the broker and between client #2 and the broker.

Question -8: What is the difference between MQTT and HTTP?

Answer -8: The following table highlights the differences between MQTT and HTTP.

Question -9: What is the difference between MQTT and CoAP?

Answer -9: The following table highlights the differences between MQTT and CoAP.

Question -10: What is the difference between MQTT and REST?

Answer -10: The following table highlights the differences between MQTT and REST.

Question -11: Which brokers are available for MQTT testing by a client?

Answer -11: The broker is a server that can be installed on any machine in the cloud. There are different types of brokers, such as HiveMQ and Mosquitto.

Question -12: What is the size of the header and payload in the MQTT protocol?

Answer -12: MQTT messages contain a mandatory fixed-length header of 2 bytes and an optional message-specific variable-length header and message payload.

This set of MQTT interview questions and answers is useful for both freshers and experienced candidates.