Event sourcing with RabbitMQ - Mini Project: Build & Apply

Event sourcing with RabbitMQ

📖 Scenario: You are building a simple event sourcing system using RabbitMQ. Events represent actions in your application, and you want to send these events to a queue so other services can process them later.This project will guide you through creating a queue, publishing events, and consuming them step-by-step.

🎯 Goal: Build a basic RabbitMQ setup where you create a queue named event_queue, publish event messages to it, and consume those events to print them out.

📋 What You'll Learn

Create a queue named event_queue

Publish three event messages with exact content to the queue

Consume messages from event_queue and print each event

Use RabbitMQ commands or Python pika library commands exactly as instructed

💡 Why This Matters

🌍 Real World

Event sourcing is used in real applications to record all changes as events. RabbitMQ helps by reliably sending and storing these events for later processing.

💼 Career

Understanding how to use RabbitMQ for event sourcing is valuable for roles in DevOps, backend development, and system architecture where event-driven design is common.

1

Create the RabbitMQ queue

Write the command to declare a queue named event_queue using RabbitMQ's rabbitmqadmin tool.

RabbitMQ

# Write the command to declare the queue named 'event_queue'
# Your code here

Hint

Use rabbitmqadmin declare queue name=event_queue durable=true to create a durable queue.

2

Publish event messages to the queue

Write three separate commands to publish these exact messages to the event_queue queue using rabbitmqadmin: 1. {"event": "user_signed_up", "user_id": 101} 2. {"event": "order_placed", "order_id": 5001} 3. {"event": "payment_received", "payment_id": 3001}

RabbitMQ

rabbitmqadmin declare queue name=event_queue durable=true
# Publish the first event message below
# Your code here

Hint

Use rabbitmqadmin publish routing_key=event_queue payload='...' for each event message.

3

Consume and print event messages

Write a command to consume messages from the event_queue queue using rabbitmqadmin and print each message to the console.

RabbitMQ

rabbitmqadmin declare queue name=event_queue durable=true
rabbitmqadmin publish routing_key=event_queue payload='{"event": "user_signed_up", "user_id": 101}'
rabbitmqadmin publish routing_key=event_queue payload='{"event": "order_placed", "order_id": 5001}'
rabbitmqadmin publish routing_key=event_queue payload='{"event": "payment_received", "payment_id": 3001}'
# Write the command to consume messages from 'event_queue'
# Your code here

Hint

Use rabbitmqadmin get queue=event_queue requeue=false to consume and print messages.

4

Display the consumed event messages

Write a command or script output that shows the three event messages printed exactly as they were published, confirming they were consumed from event_queue.

RabbitMQ

rabbitmqadmin declare queue name=event_queue durable=true
rabbitmqadmin publish routing_key=event_queue payload='{"event": "user_signed_up", "user_id": 101}'
rabbitmqadmin publish routing_key=event_queue payload='{"event": "order_placed", "order_id": 5001}'
rabbitmqadmin publish routing_key=event_queue payload='{"event": "payment_received", "payment_id": 3001}'
rabbitmqadmin get queue=event_queue requeue=false
# Show the output of consumed messages here
# Your code here

Hint

Run rabbitmqadmin get queue=event_queue requeue=false and check the printed payloads match the published events exactly.

Practice

1. What is the main purpose of event sourcing in RabbitMQ?

easy

A. To record all changes as a sequence of events

B. To delete old messages automatically

C. To speed up message delivery by skipping queues

D. To encrypt messages before sending

Solution

1. Step 1: Understand event sourcing concept

   Event sourcing means storing every change as an event, not just the current state.

2. Step 2: Connect event sourcing to RabbitMQ

   RabbitMQ can store and forward these events reliably using exchanges and queues.

3. Final Answer:

   To record all changes as a sequence of events -> Option A

4. Quick Check:

   Event sourcing = record all changes as events [OK]

Hint: Event sourcing means saving every change as an event [OK]

Common Mistakes:

• Thinking event sourcing deletes old data
• Confusing event sourcing with encryption
• Assuming event sourcing skips queues

2. Which RabbitMQ component is responsible for routing events to queues based on routing keys?

easy

A. Queue

B. Binding

C. Channel

D. Exchange

Solution

1. Step 1: Identify RabbitMQ components

   Exchanges receive messages and decide where to send them using routing keys.

2. Step 2: Role of routing keys and bindings

   Bindings connect exchanges to queues, but routing decisions happen inside exchanges.

3. Final Answer:

   Exchange -> Option D

4. Quick Check:

   Routing keys route messages via exchanges [OK]

Hint: Exchanges route messages using routing keys [OK]

Common Mistakes:

• Confusing bindings as routing decision makers
• Thinking queues route messages
• Mixing channels with routing

3. Given this RabbitMQ setup:

channel.exchange_declare(exchange='events', exchange_type='direct')
channel.queue_declare(queue='order_events')
channel.queue_bind(queue='order_events', exchange='events', routing_key='order.created')
channel.basic_publish(exchange='events', routing_key='order.created', body='Order123')

What happens when the message is published?

medium

A. Message causes an error due to missing routing key

B. Message is discarded because no queue matches

C. Message is sent to 'order_events' queue

D. Message is sent to all queues bound to 'events' exchange

Solution

1. Step 1: Analyze exchange and queue binding

   The 'events' exchange is direct type, routing key 'order.created' binds to 'order_events' queue.

2. Step 2: Check message publish routing

   Message with routing key 'order.created' matches binding, so it goes to 'order_events' queue.

3. Final Answer:

   Message is sent to 'order_events' queue -> Option C

4. Quick Check:

   Direct exchange routes by exact routing key [OK]

Hint: Direct exchange sends message only to matching routing key queue [OK]

Common Mistakes:

• Assuming message goes to all queues
• Thinking message is discarded without error
• Forgetting routing key is required

4. You wrote this code to bind a queue but it doesn't receive messages:

channel.queue_bind(queue='events_queue', exchange='events_exchange', routing_key='user.updated')

What is the most likely reason messages are not received?

medium

A. The queue was not declared before binding

B. The routing key used in publishing does not match 'user.updated'

C. The exchange type does not support routing keys

D. The channel was closed before binding

Solution

1. Step 1: Verify routing key matching

   Messages only reach queues if routing keys match bindings exactly.

2. Step 2: Check publishing routing key

   If published messages use a different routing key, queue won't get them despite binding.

3. Final Answer:

   The routing key used in publishing does not match 'user.updated' -> Option B

4. Quick Check:

   Routing keys must match for delivery [OK]

Hint: Routing keys must match exactly to deliver messages [OK]

Common Mistakes:

• Assuming exchange type blocks routing keys
• Forgetting to declare queue before binding
• Not checking if channel is open

5. You want to implement event sourcing with RabbitMQ to track user actions. Which setup best ensures all user events are stored and can be replayed later?

hard

A. Use a topic exchange with queues bound by event patterns, and enable message persistence and acknowledgments

B. Use a fanout exchange to broadcast events to multiple queues, each storing events for different services

C. Use a direct exchange with one queue per event type, but do not persist messages after consumption

D. Use a headers exchange without bindings, relying on message headers only

Solution

1. Step 1: Understand event sourcing needs

   Event sourcing requires storing all events reliably and replaying them later.

2. Step 2: Evaluate exchange types and persistence

   Topic exchange allows flexible routing by event patterns; persistence and acknowledgments ensure events are saved and not lost.

3. Step 3: Compare options

   Fanout broadcasts but may not filter; direct without persistence loses events; headers without bindings is unreliable.

4. Final Answer:

   Use a topic exchange with queues bound by event patterns, and enable message persistence and acknowledgments -> Option A

5. Quick Check:

   Topic exchange + persistence = reliable event sourcing [OK]

Hint: Use topic exchange with persistence for flexible, reliable event storage [OK]

Common Mistakes:

• Ignoring message persistence
• Using fanout without filtering
• Relying on headers exchange without bindings