What is the delivery type of a subscription by default when adding it to a topic in Cloud Pub/Sub?
When adding a subscription to a topic in Cloud Pub/Sub, the default delivery type is "PULL". Cloud Pub/Sub is a messaging service provided by Google Cloud Platform that allows for the asynchronous communication between applications. It enables publishers to send messages to topics, and subscribers to receive those messages from the topics.
In Cloud Pub/Sub, there are two types of message delivery: "PUSH" and "PULL". The delivery type determines how messages are sent from the topic to the subscription.
By default, when a subscription is added to a topic, the delivery type is set to "PULL". This means that the subscriber needs to actively request messages from the subscription using the Pub/Sub API. The subscriber can periodically pull messages from the subscription using the `projects.subscriptions.pull` method. This method will return any available messages, up to the maximum number specified in the request.
Here is an example of how to pull messages from a subscription using the Pub/Sub API in Python:
python
from google.cloud import pubsub_v1
project_id = "your-project-id"
subscription_id = "your-subscription-id"
subscriber = pubsub_v1.SubscriberClient()
subscription_path = subscriber.subscription_path(project_id, subscription_id)
response = subscriber.pull(subscription_path, max_messages=10)
for message in response.received_messages:
print(f"Received message: {message.message.data}")
# Acknowledge the received messages
ack_ids = [message.ack_id for message in response.received_messages]
subscriber.acknowledge(subscription_path, ack_ids)
On the other hand, the "PUSH" delivery type allows messages to be automatically pushed to a specified endpoint (HTTP/HTTPS) by Cloud Pub/Sub. This means that the subscriber doesn't need to actively request messages, as they are delivered directly to the endpoint. To use "PUSH" delivery, you need to configure a push endpoint URL for the subscription.
To summarize, the default delivery type of a subscription when adding it to a topic in Cloud Pub/Sub is "PULL". This means that the subscriber needs to actively pull messages from the subscription using the Pub/Sub API. However, it is also possible to configure the subscription for "PUSH" delivery if messages need to be automatically pushed to a specified endpoint.
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