Terraform - Remove the need for region specific reference data (#1962)

* Dynamically retrieve aws_bastion_ami latest reference by querying AWS rather than hard coded

* Dynamically retrieve the list of availability_zones instead of needing to have them hard coded

* Limit availability zones to first 2, using slice extrapolation function

* Replace the need for hardcoded variable "aws_cluster_ami" by the data provided by Terraform

* Move ami choosing to vars, so people don't need to edit create infrastructure if they want another vendor image (as suggested by @atoms)

* Make name of the data block agnostic of distribution, given there are more than one distribution supported

* Add documentation about other distros being supported and what to change in which location to make these changes

contrib/terraform/aws/README.md

@@ -24,7 +24,7 @@ export AWS_DEFAULT_REGION="zzz"
 ```
 - Rename `contrib/terraform/aws/terraform.tfvars.example` to `terraform.tfvars`
 
-- Update `contrib/terraform/aws/terraform.tfvars` with your data
+- Update `contrib/terraform/aws/terraform.tfvars` with your data. By default, the Terraform scripts use CoreOS as base image. If you want to change this behaviour, see note "Using other distrib than CoreOs" below.
 - Allocate a new AWS Elastic IP. Use this for your `loadbalancer_apiserver_address` value (below)
 - Create an AWS EC2 SSH Key
 - Run with `terraform apply --var-file="credentials.tfvars"` or `terraform apply` depending if you exported your AWS credentials
@@ -36,18 +36,72 @@ terraform apply -var-file=credentials.tfvars -var 'loadbalancer_apiserver_addres
 
 - Terraform automatically creates an Ansible Inventory file called `hosts` with the created infrastructure in the directory `inventory`
 
-- Ansible will automatically generate an ssh config file for your bastion hosts. To connect to hosts with ssh using bastion host use generated ssh-bastion.conf. 
+- Ansible will automatically generate an ssh config file for your bastion hosts. To connect to hosts with ssh using bastion host use generated ssh-bastion.conf.
   Ansible automatically detects bastion and changes ssh_args  
 ```commandline
-ssh -F ./ssh-bastion.conf user@$ip 
+ssh -F ./ssh-bastion.conf user@$ip
 ```
 
 - Once the infrastructure is created, you can run the kubespray playbooks and supply inventory/hosts with the `-i` flag.
 
 Example (this one assumes you are using CoreOS)
 ```commandline
-ansible-playbook -i ./inventory/hosts ./cluster.yml -e ansible_ssh_user=core -e bootstrap_os=coreos -b --become-user=root --flush-cache 
+ansible-playbook -i ./inventory/hosts ./cluster.yml -e ansible_ssh_user=core -e bootstrap_os=coreos -b --become-user=root --flush-cache
 ```
+***Using other distrib than CoreOs***
+If you want to use another distribution than CoreOS, you can modify the search filters of the 'data "aws_ami" "distro"' in variables.tf.
+
+For example, to use:
+- Debian Jessie, replace 'data "aws_ami" "distro"' in variables.tf with
+data "aws_ami" "distro" {
+  most_recent = true
+
+  filter {
+    name   = "name"
+    values = ["debian-jessie-amd64-hvm-*"]
+  }
+
+  filter {
+    name   = "virtualization-type"
+    values = ["hvm"]
+  }
+
+  owners = ["379101102735"]
+}
+
+- Ubuntu 16.04, replace 'data "aws_ami" "distro"' in variables.tf with
+data "aws_ami" "distro" {
+  most_recent = true
+
+  filter {
+    name   = "name"
+    values = ["ubuntu/images/hvm-ssd/ubuntu-xenial-16.04-amd64-*"]
+  }
+
+  filter {
+    name   = "virtualization-type"
+    values = ["hvm"]
+  }
+
+  owners = ["099720109477"]
+}
+
+- Centos 7, replace 'data "aws_ami" "distro"' in variables.tf with
+data "aws_ami" "distro" {
+  most_recent = true
+
+  filter {
+    name   = "name"
+    values = ["dcos-centos7-*"]
+  }
+
+  filter {
+    name   = "virtualization-type"
+    values = ["hvm"]
+  }
+
+  owners = ["688023202711"]
+}
 
 **Troubleshooting**