Publish-subscribe architecture in IOT Protocols - Mini Project: Build & Apply

Build a Simple Publish-Subscribe System

📖 Scenario: Imagine you are building a simple messaging system where devices can send messages to topics and other devices can receive messages from those topics. This is called a publish-subscribe system, commonly used in IoT (Internet of Things) to allow many devices to communicate efficiently.

🎯 Goal: You will create a basic publish-subscribe system in Python that stores messages by topic, allows devices to publish messages to topics, and allows devices to subscribe and receive messages from those topics.

📋 What You'll Learn

Create a dictionary to hold topics and their messages

Add a list of subscribers for each topic

Write a function to publish messages to a topic

Write a function to subscribe a device to a topic

Write a function to get all messages for a subscriber from their subscribed topics

Print the messages received by a subscriber

💡 Why This Matters

🌍 Real World

Publish-subscribe architecture is widely used in IoT devices to allow sensors and controllers to communicate without knowing about each other directly. This helps scale systems and manage many devices easily.

💼 Career

Understanding publish-subscribe systems is important for roles in IoT development, cloud messaging services, and event-driven architectures common in modern software and DevOps environments.

1

Create the topics dictionary

Create a dictionary called topics with these exact keys: 'sports', 'news', and 'weather'. Each key should have an empty list as its value to hold messages.

IOT Protocols

# Your code here

Hint

Think of topics as boxes labeled 'sports', 'news', and 'weather'. Each box will hold messages.

2

Create the subscribers dictionary

Create a dictionary called subscribers with the same keys as topics: 'sports', 'news', and 'weather'. Each key should have an empty list as its value to hold subscriber names.

IOT Protocols

topics = {'sports': [], 'news': [], 'weather': []}
# Your code here

Hint

Subscribers are like friends who want to get messages from each topic box.

3

Write publish and subscribe functions

Write two functions: publish(topic, message) that adds message to topics[topic], and subscribe(device, topic) that adds device to subscribers[topic].

IOT Protocols

topics = {'sports': [], 'news': [], 'weather': []}
subscribers = {'sports': [], 'news': [], 'weather': []}
# Your code here

Hint

Publishing means putting a message in the topic box. Subscribing means adding a device to the list of friends who get messages from that box.

4

Get messages for a subscriber and print them

Write a function get_messages(device) that returns a list of all messages from topics where device is subscribed. Then, subscribe 'device1' to 'sports' and 'news', publish messages 'Game tonight' to 'sports' and 'Elections coming' to 'news', and print the messages received by 'device1' using print(get_messages('device1')).

IOT Protocols

topics = {'sports': [], 'news': [], 'weather': []}
subscribers = {'sports': [], 'news': [], 'weather': []}

def publish(topic, message):
    topics[topic].append(message)

def subscribe(device, topic):
    subscribers[topic].append(device)

# Your code here

Hint

Think of get_messages as checking all the boxes where your device is a friend and collecting all messages inside.

Practice

1. What is the main role of a broker in a publish-subscribe architecture?

easy

A. To receive messages from publishers and forward them to subscribers

B. To directly connect publishers and subscribers

C. To store all messages permanently

D. To encrypt messages between devices

Solution

1. Step 1: Understand the broker's function

   The broker acts as a middleman that receives messages from publishers.

2. Step 2: Identify message forwarding role

   The broker forwards these messages to subscribers interested in specific topics.

3. Final Answer:

   To receive messages from publishers and forward them to subscribers -> Option A

4. Quick Check:

   Broker forwards messages [OK]

Hint: Broker forwards messages, it doesn't connect devices directly [OK]

Common Mistakes:

• Thinking broker connects devices directly
• Assuming broker stores messages permanently
• Confusing broker with encryption service

2. Which of the following is the correct way to describe a topic in publish-subscribe?

easy

A. A label used to organize messages for subscribers

B. A direct connection between two devices

C. A security protocol for message encryption

D. A device that publishes messages

Solution

1. Step 1: Define what a topic is

   A topic is a label or category that organizes messages so subscribers receive only relevant ones.

2. Step 2: Eliminate incorrect options

   Topics are not connections, security protocols, or devices.

3. Final Answer:

   A label used to organize messages for subscribers -> Option A

4. Quick Check:

   Topic organizes messages [OK]

Hint: Topics organize messages, not devices or connections [OK]

Common Mistakes:

• Confusing topics with device connections
• Thinking topics are security features
• Mixing up topics with publishers

3. Given this scenario: A device publishes messages to topic home/temperature. Which device will receive the messages?

medium

A. All devices on the network

B. Any device subscribed to home/humidity

C. Any device subscribed to home/temperature

D. Only the publishing device

Solution

1. Step 1: Identify the topic published to

   The device publishes to home/temperature.

2. Step 2: Determine which subscribers get the message

   Only devices subscribed to home/temperature receive the messages.

3. Final Answer:

   Any device subscribed to home/temperature -> Option C

4. Quick Check:

   Subscribers to topic get messages [OK]

Hint: Subscribers to the exact topic get messages [OK]

Common Mistakes:

• Assuming all devices get messages
• Thinking publishing device receives its own messages
• Confusing similar topic names

4. A subscriber is not receiving messages from the broker. Which of these is a likely cause?

medium

A. Publisher is sending messages to the subscriber directly

B. Subscriber is publishing messages instead of subscribing

C. Broker is encrypting messages incorrectly

D. Subscriber is not subscribed to the correct topic

Solution

1. Step 1: Check subscription correctness

   If the subscriber is not subscribed to the right topic, it won't get messages.

2. Step 2: Rule out other causes

   Publishers don't send messages directly; encryption issues or wrong roles are less common causes here.

3. Final Answer:

   Subscriber is not subscribed to the correct topic -> Option D

4. Quick Check:

   Correct topic subscription needed [OK]

Hint: Check subscriber's topic subscription first [OK]

Common Mistakes:

• Thinking publisher sends messages directly
• Blaming encryption without evidence
• Confusing subscriber and publisher roles

5. In a large IoT system using publish-subscribe, how can you ensure that only devices in the 'factory/floor1' area receive temperature alerts without affecting others?

hard

A. Publish all alerts to factory/temperature and let devices filter messages locally

B. Publish temperature alerts to topic factory/floor1/temperature and have devices subscribe to it

C. Send alerts directly to each device's IP address

D. Use a single topic temperature for all devices

Solution

1. Step 1: Use topic hierarchy for targeted messaging

   Publishing to factory/floor1/temperature targets only devices subscribed to that specific area.

2. Step 2: Avoid broad topics or direct device addressing

   Broad topics or direct IP messaging reduce scalability and flexibility.

3. Final Answer:

   Publish temperature alerts to topic factory/floor1/temperature and have devices subscribe to it -> Option B

4. Quick Check:

   Use specific topics for targeted delivery [OK]

Hint: Use detailed topic paths for precise message delivery [OK]

Common Mistakes:

• Using broad topics causing unwanted message delivery
• Trying direct device IP messaging in pub-sub
• Ignoring topic hierarchy benefits