Configure deployment to EKS

[robert-bo-davis]

This PR adds support for EKS.

To deploy to EKS, you should have api_server and kubernetes_certificate secrets set in drone. If drone is deploying from outside of AWS, you should also have an aws_access_key_id, aws_secret_access_key secret. An AWS_DEFAULT_REGION environmental variable should also be set for the deployment.

pipeline
  helm_deploy:
    image: quay.io/ipedrazas/drone-helm
    chart: ./charts/my-chart
    release: ${DRONE_BRANCH}
    values: image.tag=${DRONE_BRANCH}-${DRONE_COMMIT_SHA:0:7}
    prefix: STAGING
    namespace: staging
    eks_cluster: my-eks-cluster
    environment:
      - AWS_DEFAULT_REGION=us-east-1

    secrets: [ aws_access_key_id, aws_secret_access_key, api_server, kubernetes_certificate ]

fixes #78

[ipedrazas]

Hey, thanks for this contribution. Could you add a quick test to verify that the new var doesn't break anything?

thanks!

[robert-bo-davis]

Some very basic test have been and support for specifying a role ARN has been added. Thanks!