Pull vs push subscriptions in GCP - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a pull subscription in Google Cloud Pub/Sub.

GCP

gcloud pubsub subscriptions create my-subscription --topic=my-topic --[1]

Drag options to blanks, or click blank then click option'

Apush-endpoint

Bno-ack

Cpush

Dack-deadline

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'push' flag when creating a pull subscription

Omitting the acknowledgement deadline

The ack-deadline flag is used to set the acknowledgement deadline for a pull subscription. Pull subscriptions do not use the push flag.

2fill in blank

medium

Complete the code to create a push subscription with an endpoint URL.

GCP

gcloud pubsub subscriptions create my-push-sub --topic=my-topic --[1]=https://example.com/push

Drag options to blanks, or click blank then click option'

Apush-endpoint

Back-deadline

Cpush-url

Dendpoint

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'ack-deadline' instead of 'push-endpoint'

Using incorrect flag names like 'push-url'

The push-endpoint flag specifies the URL where messages are pushed in a push subscription.

3fill in blank

hard

Fix the error in the subscription creation command to correctly specify a push subscription.

GCP

gcloud pubsub subscriptions create my-sub --topic=my-topic --[1]=http://myservice.com/receive

Drag options to blanks, or click blank then click option'

Aack-deadline

Bpush

Cpush-endpoint

Dendpoint-url

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'push' instead of 'push-endpoint'

Using 'ack-deadline' for push subscriptions

The correct flag to specify the push endpoint URL is push-endpoint. Other options are invalid or incorrect.

4fill in blank

hard

Fill both blanks to configure a pull subscription with a 20-second acknowledgement deadline.

GCP

gcloud pubsub subscriptions create my-pull-sub --topic=my-topic --[1]=[2]

Drag options to blanks, or click blank then click option'

Aack-deadline

Bpush-endpoint

C20

D10

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'push-endpoint' for pull subscription

Setting acknowledgement deadline to 10 instead of 20

The ack-deadline flag sets the acknowledgement deadline, and 20 seconds is the desired value.

5fill in blank

hard

Fill all three blanks to create a push subscription with a 10-second acknowledgement deadline and a push endpoint URL.

GCP

gcloud pubsub subscriptions create my-push-sub --topic=my-topic --[1]=[2] --[3]=https://service.example.com/push

Drag options to blanks, or click blank then click option'

Aack-deadline

B10

Cpush-endpoint

Dpush-url

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'push-url' instead of 'push-endpoint'

Omitting the acknowledgement deadline

Setting wrong acknowledgement time

Push subscriptions can have an acknowledgement deadline set with ack-deadline and require the push-endpoint flag to specify the URL.

Practice

1. What is the main difference between a pull subscription and a push subscription in Google Cloud Pub/Sub?

easy

A. Pull subscriptions send messages automatically; push subscriptions require your app to request messages.

B. Pull subscriptions are faster than push subscriptions in all cases.

C. Pull subscriptions only work with HTTP; push subscriptions only work with gRPC.

D. Pull subscriptions require your app to request messages; push subscriptions send messages automatically.

Solution

1. Step 1: Understand pull subscription behavior

   Pull subscriptions require the client application to ask for messages explicitly.

2. Step 2: Understand push subscription behavior

   Push subscriptions automatically send messages to the client via HTTP POST.

3. Final Answer:

   Pull subscriptions require your app to request messages; push subscriptions send messages automatically. -> Option D

4. Quick Check:

   Pull = request, Push = automatic [OK]

Hint: Pull means ask; push means receive automatically [OK]

Common Mistakes:

• Confusing which subscription type initiates message delivery
• Thinking push requires app to poll for messages
• Assuming pull subscriptions send messages automatically

2. Which of the following is the correct way to configure a push subscription endpoint URL in Google Cloud Pub/Sub?

easy

A. Set the subscription's pushConfig with a valid HTTPS URL where messages will be sent.

B. Set the subscription's pullConfig with the endpoint URL to pull messages.

C. Configure the subscription with a TCP socket address for push delivery.

D. Use the subscription's pushConfig with an FTP URL for message delivery.

Solution

1. Step 1: Identify correct pushConfig usage

   Push subscriptions require setting pushConfig with a valid HTTPS URL for message delivery.

2. Step 2: Eliminate incorrect options

   PullConfig does not exist; TCP and FTP are not supported protocols for push endpoints.

3. Final Answer:

   Set the subscription's pushConfig with a valid HTTPS URL where messages will be sent. -> Option A

4. Quick Check:

   PushConfig needs HTTPS URL [OK]

Hint: Push subscriptions need HTTPS URL in pushConfig [OK]

Common Mistakes:

• Using pullConfig instead of pushConfig
• Setting non-HTTPS URLs for push endpoints
• Confusing pull and push subscription settings

3. Consider this code snippet for a pull subscription client in Python using Google Cloud Pub/Sub:

from google.cloud import pubsub_v1
subscriber = pubsub_v1.SubscriberClient()
subscription_path = subscriber.subscription_path('my-project', 'my-sub')
response = subscriber.pull(subscription=subscription_path, max_messages=1)
print(len(response.received_messages))

What will this code print if there is exactly one message available in the subscription?

medium

A. Error due to missing ack

B. 0

C. 1

D. None

Solution

1. Step 1: Understand pull method behavior

   The pull method requests messages; if one message is available, it returns it in received_messages.

2. Step 2: Check printed output

   len(response.received_messages) will be 1 because exactly one message is pulled.

3. Final Answer:

   1 -> Option C

4. Quick Check:

   One message pulled means length is 1 [OK]

Hint: Pull returns messages list; length matches available messages [OK]

Common Mistakes:

• Assuming pull returns zero without ack
• Expecting error if ack is missing
• Confusing pull with push subscription behavior

4. You have a push subscription configured, but your app is not receiving any messages. Which of the following is the most likely cause?

medium

A. The push endpoint URL is incorrect or unreachable.

B. The subscription is set to pull instead of push.

C. The app forgot to call pull() method.

D. The topic has no messages published.

Solution

1. Step 1: Check push subscription delivery requirements

   Push subscriptions require a reachable, correct HTTPS endpoint to deliver messages.

2. Step 2: Analyze other options

   Pull vs push setting is fixed; pull() is not used in push; no messages means no delivery but question implies messages exist.

3. Final Answer:

   The push endpoint URL is incorrect or unreachable. -> Option A

4. Quick Check:

   Push needs correct reachable URL [OK]

Hint: Push needs reachable endpoint URL [OK]

Common Mistakes:

• Confusing pull and push subscription methods
• Assuming pull() is needed for push subscriptions
• Ignoring network or URL errors

5. You want to design a system that processes messages only when your app is ready and can control the rate of message processing. Which subscription type should you choose and why?

hard

A. Push subscription, because it retries sending messages until acknowledged.

B. Pull subscription, because your app controls when to request messages.

C. Push subscription, because messages are sent automatically and fast.

D. Pull subscription, because it automatically scales message delivery.

Solution

1. Step 1: Identify control needs

   The app wants to control when and how fast messages are processed.

2. Step 2: Match subscription type to control

   Pull subscriptions let the app ask for messages when ready, controlling rate and timing.

3. Final Answer:

   Pull subscription, because your app controls when to request messages. -> Option B

4. Quick Check:

   Pull = app controls message flow [OK]

Hint: Choose pull to control message processing timing [OK]

Common Mistakes:

• Choosing push for control over message rate
• Assuming push retries mean better control
• Thinking pull auto-scales delivery