You find an Allow statement in a policy, but the request still returns AccessDenied. Adding more permissions immediately skips the most useful part of the investigation: finding which request AWS evaluated and which control rejected it. This checklist turns that investigation into a repeatable study exercise.
Identify the caller before reading the policy
The AWS CLI get-caller-identity operation returns the identity associated with the credentials used for that call. With the CLI already configured for your lab, inspect the account and ARN rather than assuming your terminal uses the same identity as your browser.
aws sts get-caller-identityRun this in the same credential context as the failing CLI request. A successful result identifies the caller; it does not prove that caller can access a bucket, decrypt data or modify a resource. If the error comes from an application, your own terminal's result is not proof of the application's identity. Redact account identifiers before sharing diagnostic notes publicly.
Describe one request precisely
| Evidence | Question to answer |
|---|---|
| Principal | Which user, role or session actually made the request? |
| Action | Which API operation failed, rather than which console page was open? |
| Resource | Which exact resource was requested, and who owns it? |
| Context | What region, tags or other relevant condition values accompanied the request? |
| Error | Does the message name a policy type or identify an explicit denial? |
AWS distinguishes an explicit denial from the absence of an applicable permission. Its troubleshooting documentation also warns that an error may identify only one denying policy type even when several apply. Treat the message as a starting point, not a complete inventory of everything that needs checking.
Separate grants from limiting controls
An applicable explicit Deny takes precedence over an Allow. For identity-policy permissions constrained by a permissions boundary, the action must fit within both. Organization policies and session policies can introduce additional restrictions. Which policies apply depends on the request; do not reduce every case to adding together all the Allow statements you can find.
A permissions boundary limits what identity-based policies can grant; it does not grant access by itself. Resource-based policies require particular care: grants to an IAM role ARN and grants directly to a role-session ARN can interact differently with implicit denies. Check the principal type against AWS's boundaries documentation before applying a simplified intersection rule.
Work through a bounded example
Imagine a lab role trying to read one object. The relevant identity policy allows the requested action on that object. The role has a permissions boundary that does not allow that action. There is no resource-based grant to the role or session, and no other applicable control changes this example. Under those stated assumptions, the identity policy cannot grant effective access outside the boundary.
Your study answer should name the boundary and explain why another identity-policy Allow would not fix this case. Then state the next decision: ask the authorized owner whether the task is intended to be permitted. That is different from assuming the boundary is a mistake. If the scenario later introduces a direct resource-based grant, revisit the analysis rather than reusing the original answer.
Use simulation as a check, not a guarantee
The IAM policy simulator evaluates policy inputs without performing the requested service operation. This makes it useful for comparing an intended grant with a restrictive control. Supply the relevant policies, action, resource and condition values. AWS documents differences between simulator results and live behavior, so a simulated Allow is not a guarantee that the real request will succeed.
- Predict the result before running the simulation and name the policy responsible.
- Compare the result with your prediction. Record missing context instead of silently changing the assumptions.
- In an authorized lab, test only the intended operation and record the actual result.
- Confirm that an operation which should remain forbidden is still denied.
Turn the diagnosis into a useful revision note
Use four lines: request, decisive evidence, conclusion, and what would change the conclusion. A note that says 'permissions issue' is too vague to help next week. A note that identifies the principal and limiting control gives you something concrete to test on a different scenario.
Use the AWS SAA-C03 study guide for the wider preparation plan, then review secure-architecture practice. Treat a correct practice answer as a prompt to explain the policy interaction, not as proof that you can diagnose every AWS authorization failure.