Redis as cache vs data store vs message broker - Hands-On Comparison

Using Redis as Cache, Data Store, and Message Broker

📖 Scenario: You are building a simple web application that needs to store user session data, cache frequently accessed product information, and send notifications between different parts of the app.Redis can help with all these tasks by acting as a cache, a data store, and a message broker.

🎯 Goal: Learn how to use Redis for three common roles: caching data, storing persistent data, and sending messages between services.You will write Redis commands step-by-step to set up each role.

📋 What You'll Learn

Create a Redis key-value pair to store user session data (data store)

Create a Redis key-value pair to cache product information (cache)

Set an expiration time for the cached product data

Use Redis Pub/Sub commands to send and receive a notification message (message broker)

💡 Why This Matters

🌍 Real World

Web applications often need fast access to session data, quick caching of product info, and real-time notifications. Redis supports all these needs efficiently.

💼 Career

Understanding Redis roles helps backend developers, DevOps engineers, and system architects build responsive and scalable systems.

1

Store user session data in Redis

Use the Redis command SET to create a key called session:user123 with the value {"username":"alice","role":"admin"}. This simulates storing user session data persistently.

Redis

# Use SET command to store session data
# Your code here

Hint

Use SET key value to store data in Redis.

2

Cache product information with expiration

Use the Redis command SET with the EX option to create a key called cache:product:456 with the value {"name":"Coffee Mug","price":12.99} that expires after 60 seconds. This simulates caching product data temporarily.

Redis

SET session:user123 "{\"username\":\"alice\",\"role\":\"admin\"}"
# Use SET with EX to cache product data with expiration
# Your code here

Hint

Use SET key value EX seconds to set a key with expiration.

3

Publish a notification message

Use the Redis command PUBLISH to send the message "New order received" to the channel notifications. This simulates sending a message between services.

Redis

SET session:user123 "{\"username\":\"alice\",\"role\":\"admin\"}"
SET cache:product:456 "{\"name\":\"Coffee Mug\",\"price\":12.99}" EX 60
# Use PUBLISH to send a notification message
# Your code here

Hint

Use PUBLISH channel message to send messages in Redis Pub/Sub.

4

Subscribe to the notification channel

Use the Redis command SUBSCRIBE to listen to the notifications channel. This simulates receiving messages sent by other parts of the app.

Redis

SET session:user123 "{\"username\":\"alice\",\"role\":\"admin\"}"
SET cache:product:456 "{\"name\":\"Coffee Mug\",\"price\":12.99}" EX 60
PUBLISH notifications "New order received"
# Use SUBSCRIBE to listen to notifications
# Your code here

Hint

Use SUBSCRIBE channel to listen for messages in Redis Pub/Sub.

Practice

1. Which of the following best describes Redis when used as a cache?

easy

A. It sends messages between different parts of an app.

B. It permanently stores large amounts of data for apps.

C. It temporarily stores data to speed up app responses.

D. It analyzes data to find patterns automatically.

Solution

1. Step 1: Understand Redis cache role

   Redis cache stores data temporarily to help apps respond faster by avoiding repeated data fetching.

2. Step 2: Compare other roles

   Permanent storage is data store, messaging is message broker, and analysis is not Redis's main role.

3. Final Answer:

   It temporarily stores data to speed up app responses. -> Option C

4. Quick Check:

   Cache = Temporary fast storage [OK]

Hint: Cache means temporary fast storage to speed apps [OK]

Common Mistakes:

• Confusing cache with permanent data store
• Thinking Redis analyzes data automatically
• Mixing message broker role with cache

2. Which Redis command is used to publish a message to a channel when Redis acts as a message broker?

easy

A. SET

B. PUBLISH

C. GET

D. SUBSCRIBE

Solution

1. Step 1: Identify publish command in Redis

   The PUBLISH command sends a message to subscribers on a channel in Redis's message broker role.

2. Step 2: Differentiate from other commands

   SET stores data, GET retrieves data, SUBSCRIBE listens to messages but does not send them.

3. Final Answer:

   PUBLISH -> Option B

4. Quick Check:

   Send message = PUBLISH [OK]

Hint: Publish sends messages; subscribe listens [OK]

Common Mistakes:

• Using SET or GET to send messages
• Confusing SUBSCRIBE with PUBLISH
• Thinking GET publishes messages

3. Consider this Redis usage: You store user session data with expiration times to speed up login checks. What role is Redis playing here?

medium

A. Cache

B. Message broker

C. Data store

D. Analytics engine

Solution

1. Step 1: Analyze session data with expiration

   Storing data with expiration to speed up access fits caching, as data is temporary and speeds up app.

2. Step 2: Exclude other roles

   Message broker sends messages, data store keeps permanent data, analytics engine is unrelated.

3. Final Answer:

   Cache -> Option A

4. Quick Check:

   Temporary session data = Cache [OK]

Hint: Temporary data with expiry means cache [OK]

Common Mistakes:

• Thinking session data is permanent storage
• Confusing message broker with cache
• Assuming analytics role for session data

4. You wrote this Redis command to send a message: SUBSCRIBE news. What is wrong if your goal was to send a message?

medium

A. SUBSCRIBE deletes the channel.

B. SUBSCRIBE command syntax is incorrect.

C. SUBSCRIBE stores messages permanently.

D. SUBSCRIBE is for receiving messages, not sending.

Solution

1. Step 1: Understand SUBSCRIBE command purpose

   SUBSCRIBE listens to messages on a channel; it does not send messages.

2. Step 2: Identify correct sending command

   To send messages, use PUBLISH, not SUBSCRIBE.

3. Final Answer:

   SUBSCRIBE is for receiving messages, not sending. -> Option D

4. Quick Check:

   SUBSCRIBE = receive, PUBLISH = send [OK]

Hint: Subscribe listens; publish sends messages [OK]

Common Mistakes:

• Using SUBSCRIBE to send messages
• Thinking SUBSCRIBE deletes channels
• Believing SUBSCRIBE stores messages

5. You want to use Redis to both speed up data access and send notifications between app parts. Which setup correctly uses Redis roles?

hard

A. Use Redis as a cache for data and use PUBLISH/SUBSCRIBE for messaging.

B. Use Redis only as a data store and ignore messaging features.

C. Use Redis as a message broker only, not for caching.

D. Use Redis to permanently store messages and cache data simultaneously.

Solution

1. Step 1: Identify Redis roles for caching and messaging

   Redis can cache data to speed access and use PUBLISH/SUBSCRIBE commands to send messages between app parts.

2. Step 2: Exclude incorrect setups

   Ignoring messaging misses notification need; message broker only misses caching; permanent message storage is not typical.

3. Final Answer:

   Use Redis as a cache for data and use PUBLISH/SUBSCRIBE for messaging. -> Option A

4. Quick Check:

   Cache + Pub/Sub = correct multi-role use [OK]

Hint: Combine cache and pub/sub for speed and messaging [OK]

Common Mistakes:

• Using Redis only for one role when multiple needed
• Trying to store messages permanently in Redis
• Ignoring pub/sub for notifications