Update system script, readme, and configuration

README.md

@@ -1,7 +1,34 @@
 # mock-ec2-metadata [![Build Status](https://travis-ci.org/NYTimes/mock-ec2-metadata.svg?branch=master)](https://travis-ci.org/NYTimes/mock-ec2-metadata)
 
 
-A simple service to mock the ec2 metadata service.
+A simple service (written in [go](https://golang.org/) using [gizmo](https://github.com/NYTimes/gizmo)) to mock the ec2 metadata service. This is usefully for development images (like vagrant or packer) that require Instance base IAM permission or other metadata information.
+
+For example, [cob](https://github.com/henrysher/cob) and [s3-iam](https://github.com/seporaitis/yum-s3-iam) can both use s3 as a yum repo. Both of these systems rely on the instances the proper credentials to have authorization to the s3 repos that yum uses.
+
+
+The metadata service normal listens on a special private ip address `169.254.169.254`. This is a special address that will not exist on your system. One option is to bind an alias to the loopback iterface. This can be done with the following command:
+
+```console
+/sbin/ifconfig lo:1 inet 169.254.169.254 netmask 255.255.255.255 up
+```
+
+Many services assume that use the metadata service uses a default port 80 and do not allow configuration or override. A simple IP talbes rule and IP forwarding can get around that, as follows:
+
+```console
+$ echo 1 > /proc/sys/net/ipv4/ip_forward
+$ iptables -t nat -A OUTPUT -p tcp -d 169.254.169.254/32 --dport 80  -j DNAT --to-destination 169.254.169.254:8111
+$ service iptables save
+```
+
+## Configuration
+All configuration is contained in either `./mock-ec2-metadata-config.json` or `/etc/mock-ec2-metadata-config.json`, the former overriding the latter.
+
+Currently the support URLs for the metadata service are:
+* http://169.254.169.154/latest/meta-data/latest/
+* http://169.254.169.154/latest/meta-data/latest/meta-data/hostname
+* http://169.254.169.154/latest/meta-data/latest/instance-id
+* http://169.254.169.154/latest/meta-data/latest/instance-type
+* http://169.254.169.154/latest/meta-data/latest/iam/security-credentials
 
 ## Getting started
 

main.go

@@ -13,7 +13,7 @@ func main() {
 
 	if _, err := os.Stat("./mock-ec2-metadata-config.json"); err == nil {
   		config.LoadJSONFile("./mock-ec2-metadata-config.json", &cfg)
-	} else if _, err := os.Stat("/etc/config.json"); err == nil  {
+	} else if _, err := os.Stat("/etc/mock-ec2-metadata-config.json"); err == nil  {
 		config.LoadJSONFile("/etc/mock-ec2-metadata-config.json", &cfg)
 	} else {
 		server.Log.Fatal("unable to locate config file")

systemd/mock-ec2-metadata.service

@@ -5,6 +5,7 @@ After=network.target
 [Service]
 Type=simple
 ExecStart=/usr/local/bin/mock-ec2-metadata
+Restart=always
 
 [Install]
 WantedBy=multi-user.target