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GCPcloud~5 mins

Policy troubleshooter in GCP - Commands & Configuration

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Introduction
Sometimes you want to know why a user can or cannot do something in Google Cloud. The Policy Troubleshooter helps you check permissions and find out what rules allow or block actions.
When a user reports they cannot access a Google Cloud resource and you want to find out why.
When you want to verify if a specific permission is granted to a user before they try an action.
When you want to debug access problems in your cloud project quickly.
When you want to check if a policy change affected user permissions.
When you want to understand which policy rule is responsible for allowing or denying access.
Commands
This command checks if the user alice@example.com has permission to get the storage bucket named my-bucket. It helps find out if access is allowed or denied and why.
Terminal
gcloud policy-troubleshoot iam --principal=user:alice@example.com --permission=storage.buckets.get --resource=//storage.googleapis.com/projects/_/buckets/my-bucket
Expected OutputExpected
Access: GRANTED Explanation: - The user alice@example.com has the role roles/storage.objectViewer on the bucket my-bucket. - This role includes the permission storage.buckets.get. No policy denies were found.
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--principal - Specifies the user or service account to check permissions for.
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--permission - Specifies the exact permission to check.
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--resource - Specifies the full resource name to check access against.
This command checks if the user bob@example.com can start the compute instance named my-instance in the specified zone and project.
Terminal
gcloud policy-troubleshoot iam --principal=user:bob@example.com --permission=compute.instances.start --resource=//compute.googleapis.com/projects/my-project/zones/us-central1-a/instances/my-instance
Expected OutputExpected
Access: DENIED Explanation: - The user bob@example.com does not have any role granting compute.instances.start on the instance my-instance. - No policy allows this permission. - Check if the user needs a role like roles/compute.instanceAdmin.v1.
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--principal - Specifies the user or service account to check permissions for.
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--permission - Specifies the exact permission to check.
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--resource - Specifies the full resource name to check access against.
Key Concept

If you remember nothing else from this pattern, remember: the Policy Troubleshooter shows exactly why a user can or cannot perform a specific action on a resource.

Common Mistakes
Using an incorrect resource name format in the command.
The tool cannot find the resource and returns an error or wrong result.
Use the full resource name with the correct service prefix and resource path as shown in examples.
Checking permissions for the wrong principal email or service account.
You get results that do not match the actual user’s access.
Double-check the principal email or service account ID before running the command.
Not specifying the exact permission to check.
The tool cannot determine the access for the intended action.
Use the exact permission string like storage.buckets.get or compute.instances.start.
Summary
Use gcloud policy-troubleshoot iam with --principal, --permission, and --resource flags to check access.
The tool explains if access is granted or denied and why, showing relevant roles and policies.
Always use the correct full resource name and exact permission to get accurate results.