Google ACE Practice Question: Ensuring Successful Operation of a Cloud Solution

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✗

  Check the Cloud Logging logs for the subscription

  Why it's wrong here

  Cloud Logging records discrete Pub/Sub events such as publish operations, ack/nack calls, and subscription configuration changes, but it does not expose continuous gauges like the current backlong size or the age of the oldest unacknowledged message. Logs are an audit trail of what happened over time, whereas backlog is a real-time state measured by a metric. Thus, checking logs may show whether messages were acknowledged, but it cannot directly tell you the current subscription backlog or consumer lag.

• ✗

  Use gcloud pubsub subscriptions describe and check the ackDeadlineSeconds

  Why it's wrong here

  The `gcloud pubsub subscriptions describe` command returns the subscription's configuration, including `ackDeadlineSeconds`, push endpoint, message retention period, and topic binding, but it does not return any current runtime metrics. `ackDeadlineSeconds` defines the time window a subscriber has to acknowledge a message before it is redelivered; it is a setting, not a measurement of how many messages are awaiting acknowledgment or the age of the oldest one. Therefore, this command cannot reveal whether a subscription is currently backlogged, only how the acknowledgement timeout is configured.

• ✗

  Check the Cloud Console Pub/Sub dashboard for the topic publish rate

  Why it's wrong here

  The Cloud Console Pub/Sub topic dashboard's publish rate shows the rate at which messages are published to the topic, which is an ingress metric and not a measure of unacknowledged work on a particular subscription. A topic can have a high publish rate while all subscriptions are keeping up, or a low publish rate while a stuck subscriber allows the oldest unacked message to age indefinitely. Backlog is a subscription-side phenomenon, so you need a subscription-level metric rather than a topic-level publish rate.

• ✓

  Use Cloud Monitoring to view the 'oldest_unacked_message_age' metric

  Why this is correct

  The `oldest_unacked_message_age` metric, available in Cloud Monitoring under `pubsub.googleapis.com/subscription/oldest_unacked_message_age`, is a gauge metric that reports, per subscription, the age of the oldest message that has not yet been acknowledged. A high or increasing value directly indicates that the subscriber is not keeping up with the message flow, representing a growing backlog. This is the standard and most direct way to detect consumer lag in Cloud Pub/Sub, making it the correct diagnostic tool for the scenario.

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