Add readme and migrate to alpine

Dockerfile

@@ -1,8 +1,9 @@
-FROM stackbrew/ubuntu:16.04
-MAINTAINER Oliver Soell "oliver@timelinelabs.com"
+FROM alpine:3.3
+MAINTAINER Vince Tse <thelazyenginerd@gmail.com>
 
-RUN apt-get update -qq
-RUN apt-get install -y python-boto python-requests
+RUN apk update
+RUN apk upgrade
+RUN apk add py-boto py-requests
 
 ADD bin/route53-presence /bin/route53-presence
 

README.md

@@ -1,4 +1,65 @@
-route53-presence
-================
+# vincetse/route53-presence
 
-Docker container which registers the local ec2 instance into route53
+Docker container which registers the local EC2 instance into Route53.
+
+This is a fork of [timelinelabs/docker-route53-presence](https://github.com/timelinelabs/docker-route53-presence) which doesn't have a Docker Hub repo.  I have updated the script so that it can handle hostnames with 3rd-level domains (i.e. host.subdomain.example.com).  I have sent a [pull request](https://github.com/timelinelabs/docker-route53-presence/pull/1) to get the change incorporated, but decided to roll on my own given that repo hasn't been updated since March 2014.
+
+```
+docker run --rm timelinelabs/docker-route53-presence -h
+usage: route53-presence [-h] [--ttl TTL] [--local] hostname
+
+Register or unregister a name in Route53.
+
+positional arguments:
+  hostname    fqdn to manipulate
+
+optional arguments:
+  -h, --help  show this help message and exit
+  --ttl TTL   ttl in seconds, default 600
+  --local     use local IP instead of public
+```
+
+## Example Usage
+
+```
+# Passing AWS keys as environment variables
+docker run --name route53-presence  \
+    -e AWS_ACCESS_KEY=XXX \
+    -e AWS_SECRET_KEY=XXX \
+    vincetse/route53-presence \
+        --ttl=300 \
+        host.subdomain.example.com
+
+# Omitting AWS keys if the EC2 instance has a role that allows Route 53 actions. See below.
+docker run --name route53-presence  \
+    vincetse/route53-presence \
+        --ttl=300 \
+        host.subdomain.example.com
+```
+
+## AWS IAM Role
+
+The AWS credentials can be omitted if the host has a valid IAM role that allows for the following permissions:
+
+```
+{
+    "Version": "2012-10-17",
+    "Statement": [
+        {
+            "Effect": "Allow",
+            "Action": [
+                "route53:GetHostedZone",
+                "route53:ChangeResourceRecordSets"
+            ],
+            "Resource": "arn:aws:route53:::hostedzone/<ZONEID>"
+        },
+        {
+            "Effect": "Allow",
+            "Action": [
+                "route53:ListHostedZones"
+            ],
+            "Resource": "*"
+        }
+    ]
+}
+```