add README for running CA on AWS

cluster-autoscaler/cloudprovider/aws/README.md

@@ -0,0 +1,79 @@
+# Cluster Autoscaler on AWS 
+The cluster autoscaler on AWS scales worker nodes within an autoscaling group. It will run as a `Deployment` in your cluster. This README will go over some of the necessary steps required to get the cluster autoscaler up and running. 
+
+## Kubernetes Version 
+Cluster autoscaler must run on v1.3.0 or greater. 
+
+## Permissions 
+The worker running the cluster autoscaler will need access to certain resources and actions:
+```json
+{
+    "Version": "2012-10-17",
+    "Statement": [
+        {
+            "Effect": "Allow",
+            "Action": [
+                "autoscaling:DescribeAutoScalingGroups",
+                "autoscaling:DescribeAutoScalingInstances",
+                "autoscaling:SetDesiredCapacity",
+                "autoscaling:TerminateInstanceInAutoScalingGroup"
+            ],
+            "Resource": "*"
+        }
+    ]
+}
+```
+Unfortunately AWS does not support ARNs for autoscaling groups yet so you must use "*" as the resource.
+
+## Deployment Specification
+Your deployment configuration should look something like this:
+```yaml
+---
+apiVersion: extensions/v1beta1
+kind: Deployment
+metadata:
+  name: cluster-autoscaler
+  labels:
+    app: cluster-autoscaler
+spec:
+  replicas: 1
+  selector:
+    matchLabels:
+      app: cluster-autoscaler
+  template:
+    metadata:
+      labels:
+        app: cluster-autoscaler
+    spec:
+      containers:
+        - image: {{ YOUR IMAGE HERE }}
+          name: cluster-autoscaler
+          resources:
+            limits:
+              cpu: 100m
+              memory: 300Mi
+            requests:
+              cpu: 100m
+              memory: 300Mi
+          command:
+            - ./cluster-autoscaler
+            - -v=4
+            - --cloud-provider=aws
+            - --skip-nodes-with-local-storage=false
+            - --nodes={{ ASG MIN e.g. 1 }}:{{ASG MAX e.g. 5}}:{{ASG NAME e.g. k8s-worker-asg}}
+          env:
+            - name: AWS_REGION
+              value: us-east-1
+          volumeMounts:
+            - name: ssl-certs
+              mountPath: /etc/ssl/certs/ca-certificates.crt
+              readOnly: true
+          imagePullPolicy: "Always"
+      volumes:
+        - name: ssl-certs
+          hostPath:
+            path: "/etc/ssl/certs/ca-certificates.crt"
+```
+Note: 
+- the `/etc/ssl/certs/ca-certificates.crt` should exist by default on your ec2 instance.
+- at the time of writing this, cluster autoscaler is unaware of availability zones, the availability zone of the instance should be configured by the autoscaling group. Although autoscaling groups can contain instances in multiple availability zones, the autoscaling group should span 1 availability zone for the cluster autoscaler to work.