Publishing messages in GCP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main purpose of publishing messages in Google Cloud Pub/Sub?

Publishing messages means sending data to a topic so other services can receive and process it asynchronously.

beginner

What is a 'topic' in the context of publishing messages?

A topic is like a mailbox where messages are sent. Publishers send messages to a topic, and subscribers receive messages from it.

intermediate

Which method is used to publish a message to a topic in Google Cloud Pub/Sub?

The method is called 'publish'. It sends the message data to the topic for delivery to subscribers.

intermediate

Why is publishing messages asynchronously beneficial?

It allows the sender to continue working without waiting for the message to be delivered, improving speed and efficiency.

advanced

What happens if a message fails to publish in Google Cloud Pub/Sub?

The publisher receives an error and can retry sending the message to ensure it reaches the topic.

What is the first step to send a message in Google Cloud Pub/Sub?

A Create or select a topic

B Create a subscription

C Delete a topic

D Pull messages

You must have a topic to publish messages to before sending any data.

Which of these best describes a message in Pub/Sub?

A A piece of data sent to a topic

B A user account

C A storage bucket

D A virtual machine

Messages are the data units sent to topics for subscribers to receive.

What does the 'publish' method return after sending a message?

A The message content

B A message ID confirming successful send

C The subscriber list

D The topic name

The publish method returns a unique message ID to confirm the message was accepted.

Why might you want to retry publishing a message?

A To create a subscription

B To send duplicate messages intentionally

C To delete the topic

D Because the first attempt failed

If publishing fails, retrying helps ensure the message is delivered.

Which service in GCP is used for publishing messages?

A Compute Engine

B Cloud Storage

C Cloud Pub/Sub

D BigQuery

Cloud Pub/Sub is the messaging service for publishing and subscribing to messages.

Explain the process of publishing a message in Google Cloud Pub/Sub.

Think about how you send a letter to a mailbox and get a receipt.

Describe what happens if a message fails to publish and how to handle it.

Consider what you do if your letter doesn't get delivered the first time.

Practice

1. What is the main purpose of publishing messages in Google Cloud Pub/Sub?

easy

A. To send data to a topic so other services can receive it

B. To store data permanently in a database

C. To create virtual machines automatically

D. To monitor network traffic in real-time

Solution

1. Step 1: Understand the role of publishing in Pub/Sub

   Publishing messages means sending data to a topic so subscribers can get it.

2. Step 2: Compare with other options

   Storing data, creating VMs, or monitoring traffic are unrelated to publishing messages.

3. Final Answer:

   To send data to a topic so other services can receive it -> Option A

4. Quick Check:

   Publishing = sending data to topic [OK]

Hint: Publishing means sending messages to topics for others [OK]

Common Mistakes:

• Confusing publishing with storing data
• Thinking publishing creates resources like VMs
• Mixing publishing with monitoring tasks

2. Which of the following is the correct way to publish a message using the Google Cloud Pub/Sub Python client?

easy

A. publisher.send_message(topic_path, data="Hello World")

B. publisher.publish(topic_path, data=b"Hello World")

C. publisher.publish(topic_path, message="Hello World")

D. publisher.send(topic_path, "Hello World")

Solution

1. Step 1: Recall the correct method and parameters

   The correct method is publish(), and the message data must be bytes, so data=b"Hello World".

2. Step 2: Check other options for errors

   send() and send_message() are not valid methods; also, data must be bytes, not string.

3. Final Answer:

   publisher.publish(topic_path, data=b"Hello World") -> Option B

4. Quick Check:

   Use publish() with bytes data [OK]

Hint: Use publish() method with bytes data to send messages [OK]

Common Mistakes:

• Passing string instead of bytes as data
• Using incorrect method names like send()
• Using wrong parameter names like message=

3. Given the following Python code snippet, what will be printed?

from google.cloud import pubsub_v1
publisher = pubsub_v1.PublisherClient()
topic_path = publisher.topic_path('my-project', 'my-topic')
future = publisher.publish(topic_path, b'Message 1')
print(future.result())

medium

A. The content of the message 'Message 1'

B. The topic path string

C. An error because publish() returns None

D. The message ID of the published message

Solution

1. Step 1: Understand what publish() returns

   publish() returns a future that resolves to the message ID after publishing.

2. Step 2: Understand future.result() behavior

   Calling future.result() waits for publishing to complete and returns the message ID string.

3. Final Answer:

   The message ID of the published message -> Option D

4. Quick Check:

   future.result() = message ID [OK]

Hint: future.result() returns message ID after publish completes [OK]

Common Mistakes:

• Expecting future.result() to return message content
• Thinking publish() returns None
• Confusing topic path with message ID

4. You wrote this code to publish a message but get a TypeError: 'str' object cannot be interpreted as bytes. What is the mistake?

publisher.publish(topic_path, 'Hello World')

medium

A. The message data must be bytes, not a string

B. The topic_path variable is not defined

C. publish() method does not exist

D. You must call future.result() after publish()

Solution

1. Step 1: Identify the error cause

   The error says a string was given where bytes are expected.

2. Step 2: Fix the data type for message

   Message data must be bytes, so prefix string with b like b'Hello World'.

3. Final Answer:

   The message data must be bytes, not a string -> Option A

4. Quick Check:

   Message data = bytes, not string [OK]

Hint: Always prefix message with b to make bytes [OK]

Common Mistakes:

• Passing string instead of bytes as message data
• Ignoring error message details
• Assuming publish() method is missing

5. You want to publish multiple messages to a topic and ensure all are delivered before your program exits. Which approach is best?

hard

A. Publish messages using a loop but do not wait for any future results

B. Publish all messages and ignore the futures, then exit immediately

C. Publish each message and call future.result() immediately to wait for delivery

D. Publish messages and call future.cancel() to stop waiting

Solution

1. Step 1: Understand message delivery confirmation

   Calling future.result() waits for the message to be confirmed as delivered.

2. Step 2: Ensure program waits for all messages

   Waiting on each future ensures no message is lost before program exits.

3. Step 3: Evaluate other options

   Ignoring futures or cancelling them risks losing messages; not waiting is unsafe.

4. Final Answer:

   Publish each message and call future.result() immediately to wait for delivery -> Option C

5. Quick Check:

   Wait on future.result() to confirm delivery [OK]

Hint: Wait on future.result() for each message to confirm delivery [OK]

Common Mistakes:

• Ignoring futures and exiting too soon
• Cancelling futures instead of waiting
• Assuming publish() is synchronous