I am using latest version of s3cmd 1.5.2. As per this post, 1.5.0-alpha2 supports IAM Roles, so I am assuming this must be supported in 1.5.2 as well. I added "security_token" in s3cfg file as mentioned in this post. But I am still getting error "ERROR: S3 error: The AWS Access Key Id you provided does not exist in our records." Am I doing something wrong or this version doesn't support IAM Roles?
I figured out the answer myself. After diving into the s3cmd code, found out that instead of adding "security_token" as mentioned in the post and other sources, we need to add "access_token" in the s3cfg file. If you are using s3cmd on a cluster associated with a role then there is no need to pass any s3cfg file as well. All releases from 1.5.0-alpha2 and above support IAM Roles.