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.