Error registering: NoCredentialProviders: no valid providers in chain ECS agent error

It was a problem with trust relationships in the role as the role should include ec2. Unfortunately the error message was not all that helpful.

Example of trust relationship:

{
  "Version": "2008-10-17",
  "Statement": [
    {
      "Action": "sts:AssumeRole",
      "Principal": {
        "Service": ["ecs.amazonaws.com", "ec2.amazonaws.com"]
      },
      "Effect": "Allow"
    }
  ]
}