Add README for aws_domain_redirect.

Author: jareware

aws_domain_redirect/README.md

@@ -0,0 +1,37 @@
+# aws_domain_redirect
+
+Creates the necessary resources on AWS to implement an HTTP redirect from a domain (e.g. `redir.example.com`) to a given URL (e.g. `https://www.futurice.com/careers/women-who-code-helsinki`). Useful for creating human-friendly shortcuts for deeper links into a site, or for dynamic links (e.g. `download.example.com` always pointing to your latest release).
+
+Implementing this on AWS actually requires quite a few resources:
+
+- DNS records on [Route 53](https://aws.amazon.com/route53/)
+- A [CloudFront](https://aws.amazon.com/cloudfront/) distribution for SSL termination, for allowing secure redirection over HTTPS
+- An SSL certificate for the distribution from [ACM](https://aws.amazon.com/certificate-manager/)
+- An [S3](https://aws.amazon.com/s3/) bucket with the relevant [redirect rules](https://docs.aws.amazon.com/AmazonS3/latest/dev/how-to-page-redirect.html#advanced-conditional-redirects)
+
+Luckily, this module encapsulates this configuration quite neatly.
+
+## Example
+
+Assuming you have the [AWS provider](https://www.terraform.io/docs/providers/aws/index.html) set up, and a DNS zone for `example.com` configured on Route 53:
+
+```tf
+# "To use an ACM Certificate with CloudFront, you must request or import the certificate in the US East (N. Virginia) region."
+# https://docs.aws.amazon.com/acm/latest/userguide/acm-services.html
+# https://www.terraform.io/docs/configuration/providers.html#multiple-provider-instances
+provider "aws" {
+  alias                   = "acm_provider" # the aws_domain_redirect module expects an "aws" provider with this alias to be present
+  shared_credentials_file = "./aws.key"    # make sure you customize this to match your regular AWS provider config
+  region                  = "us-east-1"    # this is the important bit, due to the aforementioned limitation of AWS regions and ACM
+}
+
+module "my_redirect" {
+  # Check for updates at: https://github.com/futurice/terraform-utils/compare/v3.0...master
+  source = "git::ssh://[email protected]/futurice/terraform-utils.git//aws_domain_redirect?ref=v3.0"
+
+  redirect_domain = "go.example.com"
+  redirect_url    = "https://www.futurice.com/careers/"
+}
+```
+
+Applying this **will take a very long time**, because both ACM and especially CloudFront are quite slow to update. After that, both `http://go.example.com` and `https://go.example.com` should redirect clients to `https://www.futurice.com/careers/`.