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Messaging & Queues.
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01

What is message queuing and why is it important in distributed systems?

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Message queuing is an asynchronous communication pattern where messages are stored in a queue until processed by consumers. It enables decoupling between producers and consumers.

Key benefits:

  • Decoupling: Producers and consumers operate independently
  • Reliability: Messages persist even if services fail
  • Scalability: Add more consumers to handle increased load
  • Fault tolerance: System continues operating during service failures
  • Load balancing: Work distributed across multiple consumers
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02

Explain the difference between synchronous and asynchronous messaging.

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Synchronous messaging:

  • Sender waits for a response before continuing
  • Blocking operation
  • Direct communication (like HTTP request/response)
  • Example: REST API calls, gRPC
    Asynchronous messaging:
  • Sender doesn't wait for a response
  • Non-blocking operation
  • Messages are typically queued
  • Example: Message queues, event streams
# Synchronous
response = api_client.get_user(user_id)  # Blocks until response
process_user(response)
# Asynchronous
queue.publish("user_requested", {"user_id": user_id})  # Returns immediately
# Consumer processes this later
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03

What are the main components of a messaging system?

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Core components:

  • Producer/Publisher: Creates and sends messages
  • Consumer/Subscriber: Receives and processes messages
  • Message Broker: Middleware that routes messages between producers and consumers
  • Queue/Topic: Storage mechanism for messages
  • Message: The actual data being transmitted
    Additional components:
  • Exchange: Routes messages to appropriate queues (in systems like RabbitMQ)
  • Dead Letter Queue: Stores messages that couldn't be processed
  • Connection/Channel: Network connections and logical channels for communication
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04

What is the difference between a queue and a topic?

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Queue (Point-to-Point):

  • One message is consumed by exactly one consumer
  • Load balancing pattern
  • Message is removed after consumption
  • Example: Task distribution
    Topic (Publish-Subscribe):
  • One message can be consumed by multiple subscribers
  • Broadcasting pattern
  • Each subscriber gets a copy of the message
  • Example: Event notifications
Queue:    Producer → [Queue] → Consumer1 OR Consumer2
Topic:    Producer → [Topic] → Consumer1 AND Consumer2 AND Consumer3
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05

Explain the work queue pattern and its use cases.

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The work queue (task queue) pattern distributes time-consuming tasks among multiple workers. One producer sends tasks to a queue, and multiple consumers process them.
Characteristics:

  • Round-robin distribution by default
  • Each message processed by exactly one worker
  • Enables horizontal scaling
    Use cases:
  • Image processing
  • Email sending
  • Report generation
  • Data processing pipelines
# Producer
for task in tasks:
    queue.put(task)
# Multiple consumers
def worker():
    while True:
        task = queue.get()
        process_task(task)
        queue.task_done()
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06

What is message acknowledgment and why is it important?

Part of Pro
07

What is a dead letter queue and when should you use it?

Part of Pro
08

Explain the publish-subscribe pattern and its variants.

Part of Pro
Intermediate 17
09

What are the advantages and disadvantages of using message queues?

Part of Pro
10

What is a priority queue and when would you use it?

Part of Pro
11

Describe the competing consumers pattern.

Part of Pro
12

What is a delayed queue and how is it implemented?

Part of Pro
13

Compare Apache Kafka, RabbitMQ, and Amazon SQS.

Part of Pro
14

What are Kafka partitions and why are they important?

Part of Pro
15

Explain Kafka consumer groups and their benefits.

Part of Pro
16

What is RabbitMQ exchange and what types exist?

Part of Pro
17

Explain the different message delivery guarantees: at-most-once, at-least-once, and exactly-once.

Part of Pro
18

How do you scale message consumers horizontally?

Part of Pro
19

What factors affect messaging system performance?

Part of Pro
20

Explain message batching and its trade-offs.

Part of Pro
21

How do you monitor messaging system performance?

Part of Pro
22

How do you implement retry mechanisms in messaging systems?

Part of Pro
23

What are poison messages and how do you handle them?

Part of Pro
24

What are the advantages and challenges of event-driven architecture?

Part of Pro
25

Compare synchronous vs asynchronous communication in microservices.

Part of Pro
Expert 13
26

How do you implement exactly-once semantics in messaging systems?

Part of Pro
27

How do you maintain message ordering in distributed systems?

Part of Pro
28

What is the difference between total ordering and partial ordering in messaging?

Part of Pro
29

How do you implement event sourcing with message queues?

Part of Pro
30

What is the saga pattern and how is it implemented with messaging?

Part of Pro
31

How do you handle distributed transactions with messaging?

Part of Pro
32

What is CQRS and how does it relate to messaging systems?

Part of Pro
33

How do you implement message versioning and schema evolution?

Part of Pro
34

Explain message encryption and security in messaging systems.

Part of Pro
35

What are the challenges of implementing messaging in cloud environments?

Part of Pro
36

How do you design a messaging system for high availability?

Part of Pro
37

What is message deduplication and how do you implement it?

Part of Pro
38

How do you handle message ordering guarantees across multiple partitions?

Part of Pro

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