AWS IAM: Fix "Explicit Deny" for Location Service (GeoPlaces) Access

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If you’re running into permission errors when trying to use Amazon Location Service from your server-side application, here’s a straightforward way to troubleshoot and resolve the issue.

First, make sure your IAM user has the proper permissions. In your case, you’ve attached a policy that permits all geo actions with wildcards like “geo:*,” which usually covers all Location Service features. However, despite this, you still get an error stating you’re explicitly denied access.

Here’s what you should do:

Check for Explicit Deny Policies:
Sometimes, an explicit deny policy overrides allow permissions. Even if your user policy looks fine, ensure there are no Deny statements attached directly to your user, group, or on the resource itself. Also, verify there are no Service Control Policies (SCPs) in AWS Organizations that could restrict access.

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Review Policy Attachments:
Double-check that the policy is attached directly to your user rather than through a group or role that might have restrictions. Policies attached indirectly could introduce conflicts.
Verify Resource ARNs and Permissions:
Although using “Resource”: “*” in your IAM policy should suffice, confirm that the resources you’re accessing do not have additional restrictions. For location services, typically, wildcards are accepted, but consult the latest AWS documentation in case specific ARNs are needed.
Confirm Environment Variables and Credentials:
Your environment variables (AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY, AWS_REGION) are crucial. Verify they are correctly set and that the access key used matches the IAM user with the right permissions.
Test with a Fresh Set of Credentials:
You mentioned rotating keys — continue to do so if needed. Generate new access keys, update your environment variables, and test the connection again.
Use the AWS SDK Correctly:
Your code looks correct, but ensure no typos or misconfigurations exist in the query. Also, confirm your serverless environment (Railway) isn’t overriding or blocking these environment variables.
Consider Account Restrictions:
Check if there are any account-level restrictions or customer-managed policies, restrictions on specific services, or network access controls that might block API calls to Amazon Location Service.
Avoid Using an API Key for Server to API Calls:
For server-side applications, IAM credentials are recommended. API keys are better suited for client-side authentication. Since you are already using IAM, focus on resolving permission conflicts.

If after trying these steps, you still face the same error, contact AWS Support. Provide them with the full error message, the policies attached, and details of your setup. They can help identify if there are account-specific restrictions or hidden policies causing this issue.

By thoroughly reviewing permissions, policies, and configurations, you should be able to identify the source of the explicit deny and fix it. Keep your policies simple, ensure no conflicting Deny statements exist, and verify your credentials are correctly configured. These steps usually resolve most permission-related problems with AWS services.