Message retention and acknowledgment in GCP - Commands & Configuration

Introduction

When you send messages between services, you want to make sure they are not lost and are processed only once. Message retention keeps messages available for a time, and acknowledgment tells the system you received and handled a message.

When you want to keep messages available for a short time in case the receiver is slow or temporarily down

When you want to confirm that a message was processed so it is not sent again

When you want to control how long unacknowledged messages stay in the system before being redelivered

When you want to avoid losing messages during network or service interruptions

When you want to manage message flow to prevent overload on your processing service

Config File - subscription.yaml

subscription.yaml

apiVersion: pubsub.cnrm.cloud.google.com/v1beta1
kind: PubSubSubscription
metadata:
  name: example-subscription
spec:
  topicRef:
    name: example-topic
  ackDeadlineSeconds: 20
  retainAckedMessages: true
  messageRetentionDuration: 600s

This file creates a subscription to a Pub/Sub topic.

ackDeadlineSeconds sets how many seconds the subscriber has to acknowledge a message before it is redelivered.

retainAckedMessages keeps messages even after acknowledgment for the retention duration.

messageRetentionDuration sets how long messages are kept (600s = 10 minutes).

Commands

This command creates a subscription named 'example-subscription' to the topic 'example-topic'. It sets the acknowledgment deadline to 20 seconds, retains acknowledged messages, and keeps messages for 10 minutes.

Terminal

gcloud pubsub subscriptions create example-subscription --topic=example-topic --ack-deadline=20 --retain-acked-messages --message-retention-duration=600s

Expected Output

Created subscription [example-subscription].

→

--ack-deadline - Sets how long to wait for message acknowledgment before redelivery

→

--retain-acked-messages - Keeps messages after acknowledgment for the retention duration

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--message-retention-duration - Sets how long messages are retained

This command pulls one message from the subscription and automatically acknowledges it, telling the system the message was received and processed.

Terminal

gcloud pubsub subscriptions pull example-subscription --auto-ack --limit=1

Expected Output

DATA: "Hello, world!"

ACK ID: ACK_ID_1234567890

→

--auto-ack - Automatically acknowledges the message after pulling

→

--limit - Limits the number of messages pulled

This command shows the current settings of the subscription, including acknowledgment deadline and message retention settings.

Terminal

gcloud pubsub subscriptions describe example-subscription

Expected Output

name: projects/my-project/subscriptions/example-subscription

ackDeadlineSeconds: 20

retainAckedMessages: true

messageRetentionDuration: 600s

Key Concept

If you remember nothing else from this pattern, remember: acknowledgment tells the system you processed a message, and retention keeps messages available for a set time even after acknowledgment.

Common Mistakes

Not acknowledging messages after pulling them

Messages will be redelivered repeatedly, causing duplicate processing

Always acknowledge messages after processing, either manually or with auto-ack flags

Setting acknowledgment deadline too short

Messages may be redelivered before processing finishes, causing duplicates

Set acknowledgment deadline long enough for your processing time

Not enabling message retention when needed

Messages are deleted immediately after acknowledgment, losing history or retry options

Enable retainAckedMessages and set messageRetentionDuration if you want to keep messages after acknowledgment

Summary

Create a subscription with acknowledgment deadline and message retention settings.

Pull messages and acknowledge them to prevent redelivery.

Check subscription settings to verify retention and acknowledgment configurations.