Cloudwatch datasource error

Hi everyone!

I am using Grafana v6.0.1.
For some reason Cloudwatch datasource test fails with following error:

Here is grafana.log output:

t=2019-03-14T09:12:55+0000 lvl=eror msg="Metric request error" logger=context userId=1 orgId=1 uname=admin error="Failed to call ec2:getAwsConfig, InvalidParameter: 1 validation error(s) found.\n- minimum field size of 20, AssumeRoleInput.RoleArn.\n"

AWS Role is configured with required policy:

            "Sid": "AllowReadingMetricsFromCloudWatch",
            "Effect": "Allow",
            "Action": [
            "Resource": "*"

Listing metrics using aws cli works fine but Grafana fails to setup cloudwatch datasource.

I’m getting the same UI and log error for Grafana v6.2.5 (6082d19)

Can list metrics from the EC2 cli with aws cli.

Created policy per