Google ACE Practice Question: A developer has deployed a Cloud Run service but…

A developer has deployed a Cloud Run service but receives a 503 error when accessing it. The service logs show 'The request was aborted because there was no available instance.' What is the most likely cause?

⚠ Common exam trap

Google Cloud often tests the distinction between scaling limits (max instances) and resource constraints (memory/CPU), where candidates mistakenly attribute 503 errors to resource limits rather than the explicit scaling cap.

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

The service is experiencing a spike in traffic and the max instances are too low.

The 503 error with the message 'The request was aborted because there was no available instance' indicates that all current instances are saturated and Cloud Run cannot scale up quickly enough to handle the incoming requests. This occurs when traffic spikes exceed the configured maximum number of instances, causing new requests to be rejected until an instance becomes free. Option C correctly identifies that the max instances setting is too low for the traffic spike.

Answer analysis

Option-by-option breakdown

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

✗
The minimum number of instances is set too high.
Why it's wrong here
The minimum number of instances being set too high actually keeps a larger pool of warm instances ready, which reduces the likelihood of a 'no available instance' error during traffic surges. Cloud Run scales up to the maximum, and a high minimum ensures at least that many instances exist, so it would not cause requests to be rejected for lack of capacity. Therefore this is incorrect.
✗
The container health checks are failing.
Why it's wrong here
When container health checks fail, Cloud Run marks those instances as unhealthy and stops sending them traffic, but it will create replacements, so you would see startup failures or 503s due to unhealthy endpoints, not a message about no available instance. The error 'no available instance' specifically indicates that all currently running instances are saturated and the service has reached its maximum instance count. Thus, failing health checks are a different failure mode.
✓
The service is experiencing a spike in traffic and the max instances are too low.
Why this is correct
The error 'no available instance' occurs when a request arrives and all existing Cloud Run instances are processing requests, and the service has already reached its configured maximum number of instances. Cloud Run can only scale out to the max-instances setting; if that cap is too low relative to a spike in traffic, new requests are rejected with HTTP 503 and this log message. Increasing max instances or using instance-based concurrency tuning can mitigate this.
✗
The service's memory limit is set too low.
Why it's wrong here
Setting a memory limit too low would cause the container to be killed for exceeding memory (OOMKilled), leading to instance restarts or crashes, not a message about having no available instance. Cloud Run requests would fail with a different error, such as container memory limit exceeded or a 500 error, not a 503 indicating capacity exhaustion. Therefore, memory misconfiguration is not the cause.

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Google ACE Practice Question: A developer has deployed a Cloud Run service but…

Why each option matters

Option-by-option breakdown

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