Sending AWS EC2 RestAPI using Postman returns error

Question

I am trying to send a EC2 RestAPI (DescribeInstances) using Postman application. I created a user in IAM in AWS. I generated a AccessKeyId and SecretKey for that particular user, and gave the user "AmazonEC2FullAccess" policy (all EC2 access). I used the following steps in Postman to send the ResAPI:

• "Get" operation, set End Point to https://ec2.amazonaws.com/?Action=DescribeInstances

• In the "Authorization" Tab, selected "AWS Signature" and set the following fields:

  • AccessKey = ACCESSKEYEXAMPLE
  • SecretKey = SECRETKEYEXAMPLE
  • AWS Region = us-west-1
  • Service Name = ec2

• Click on "Update Request", which ends up generating 3 Headers. I used the info from the generated Headers to modify the endpoint as follows:

https://ec2.amazonaws.com/?Action=DescribeInstances&Version=2016-11-15&X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=ACCESSKEYEXAMPLE/20170913/us-west-1/ec2/aws4_request&X-Amz-Date=20170913T013055Z&X-Amz-SignedHeaders=content-type&X-Amz-Signature=amzsignaturesamplegenerated

• "Content-Type" header is set to "application/x-www-form-urlencoded", and deleted X-Amz-Date and Authorization headers.

When I sent the RestAPI by clicking on "Send", I get the following error response: Status : "401 Unauthorized" AuthFailureAWS was not able to validate the provided access credentials4bc49d04-2115-4b95-8af5-5ac879ac5df3

The error seems to suggest a malformed RestAPI as opposed to an unauthorized access. Tried different variations, very confused. Any help would be highly appreciated.

Thank you, Ahmed.

Answer 1

Just to complement @chriscatfr answer, here is a screenshot how to set postman parameters to query for instances in us-east-1 region:

Answer 2

I just found the solution to the same issue. Your URL should be:

https://ec2.us-west-1.amazonaws.com/?Action=DescribeInstances&Version=2016-11-15

It didn't work until I added &Version=2016-11-15 and the region.

This AWS Documentation page says that Version is mandatory