Changed creation of AWS Session object

[spaghettifunk]

@rusenask I see some potential issues in the design of the https://github.com/keel-hq/keel/tree/master/extension/credentialshelper/aws. The major issue is in the fact that the method GetCredentials(...) has a dependency on the aws.Session object. By instantiating this object inside this method, I cannot test it locally because I cannot set up the region and endpoint (for accessing a local service such as moto or localstack). I tried few ways but it's either very ugly or I break the CredentialsHelper interface.

What I am not happy with, is the fact that I cannot make a proper unit-test without either make it very ugly or breaking the interface. Using a bit more Dependency Injection for this type of issue would benefit the code base I believe.

I'm 100% sure that you (or whoever) had very good reasons to design it that way but I would be happy to contribute in re-thinking a little bit the design of the interface 😄

Anyway, I tested this version in our production cluster. I post here also the policy we have to use to make it work properly

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "ecr:*",
                "ec2:*"
            ],
            "Resource": "*"
        }
    ]
}

For some reasons, without the ec2:* it doesn't work at all. There is something in the ECR aws-sdk-go (I haven't investigate due to lack of time) that has a dependency on EC2 policy. I tried many different policies and this one is the only one that works.

It solves #425

[rusenask]

Hi, I agree that it's not a nice interface to test against. Maybe https://github.com/keel-hq/keel/blob/master/extension/credentialshelper/aws/aws.go#L31 could be moved into https://github.com/keel-hq/keel/blob/master/cmd/keel/main.go package where it's assembled and registered?

There was no good reason to do it either :) I am not using aws personally so can't do much testing either on it.

[spaghettifunk]

I give it a go, otherwise do you think we can merge it as it is? If not, I will try to re-define the way credentials are passed and see if I can manage to have a better local tests 😄

[rusenask]

Could you please also create a PR for https://github.com/keel-hq/keel.sh/tree/master/docs#polling-with-aws-ecr with some help on how to configure AWS (probably that policy JSON)