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cb29b2b Aug 30, 2013
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Site to site (office to Amazon VPC)

Amazon Virtual Private Cloud (Amazon VPC) lets you provision a logically isolated section of the Amazon Web Services (AWS) cloud where you can launch AWS resources in a virtual network that you define. You have complete control over your virtual networking environment, including selection of your own IP address range, creation of subnets, and configuration of route tables and network gateways.

Creating and configuring a VPC can be a daunting and complex task, so we've created a cloudformation template (see contrib) which automatically creates a VPC, internet gateway, public and private subnets, security groups, launches a TurnKey OpenVPN NAT instance preseeded with the server profile and configuration, allocates and associates an elasticip to the OpenVPN instance and configures routing.

Topology

office                                                                 vpc
172.16.0.0/16                                                  10.0.0.0/16
+--------------+-----------+                  +---------+----------------+
|              | openvpn   | <=> internet <=> | openvpn |                |
|              +-----------+                  +---------+                |
| dmz                      |                  |               subnet_pub |
| 172.16.0.0/24            |                  |              10.0.0.0/24 |
+--------------------------+                  +--------------------------+
| lan                      |                  |               subnet_pvt |
| 172.16.1.0/24            |                  |              10.0.1.0/24 |
+--------------------------+                  +--------------------------+

Assumptions and objectives

It's assumed the office network (excluding openvpn) is already configured.

Our objective is to create the VPC, 2 OpenVPN servers (one acting as a server, the other as a client), and have computers in the office LAN connect seamlessly and securely via the VPN to servers in the VPC private subnet.

Step 1: Setup VPC with TurnKey OpenVPN (server)

The easiest way to setup and configure the VPC including OpenVPN is to use the cloudformation template (see contrib for other alternatives).

Note that the TurnKey OpenVPN server profile will need to be configured with the following:

  • Email address for the OpenVPN server key (e.g., admin@example.com)
  • FQDN of server reachable by clients (e.g., vpn.example.com)
  • CIDR subnet behind server for clients to reach (e.g., 10.0.1.0/24)

The FQDN should be configured to point to the elastic IP of the OpenVPN server, which is displayed once the CFM stack is created.

Finally, you can launch servers in the private subnet. When doing so, the security group for the private subnet instances (created during VPC creation) should be specified.

Step 2: Install TurnKey OpenVPN in Office DMZ (client)

Once installation is complete, the server will reboot. On first boot it will prompt for the OpenVPN profile to use, in which case client should be selected.

Step 3: Create a profile for the Office OpenVPN client

The office OpenVPN client needs to authenticate to the VPC OpenVPN server. To do this, create a profile on the server for the client and restart the service:

$ ssh root@vpn.example.com

$ openvpn-addclient -h
  Syntax: openvpn-addclient client-name client-email [private-subnet]
  Generate keys and configuration for a new client

  Arguments:

      client-name         Unique name for client
      client-email        Client email address
      private-subnet      CIDR subnet behind client (optional)

$ openvpn-addclient office office@example.com 172.16.1.0/24
  INFO: generated /etc/openvpn/easy-rsa/keys/office.ovpn

$ /etc/init.d/openvpn restart

Step 4: Securely transfer the client profile to the Office OpenVPN client

The profile includes secret information, so it should be transfered to the client via an encrypted channel, such as RSYNC over SSH or SCP:

SRC: vpn.example.com:/etc/openvpn/easy-rsa/keys/office.ovpn
DST: dmz-openvpn:/etc/openvpn/office-to-vpc.conf

Note that in the above example the profile extension has changed from ovpn to conf so the connection will be created at server boot by the openvpn initscript.

Lastly, start the VPN connection:

$ /etc/init.d/openvpn start

You should now be able to connect from the office OpenVPN server to servers in the VPC private subnet, for example:

$ ssh root@10.0.1.x

For computers on the office LAN to transparently use the VPN connection, routing needs to be configured to direct 10.0.0.0/24 to the OpenVPN client.

Step 5: Mobile device (optional)

For example sake, lets say that Joe needs access to the servers on the VPC private subnet when he is on the go via his mobile device.

The first thing to do is create a profile:

$ ssh root@vpn.example.com

$ openvpn-client joe-mobile joe@example.com
  INFO: generated /etc/openvpn/easy-rsa/keys/joe-mobile.ovpn

Next, the profile needs to be securely imported into Joe's mobile device. Unfortunately, it does not support encrypted email, nor does it have an SD card slot.

For cases like this, TurnKey OpenVPN supports auto-expiring obfuscated URLs for downloading client profiles via a web browser using HTTPS:

$ /var/www/openvpn/bin/addprofile joe-mobile
  URL: https://vpn.example.com/profiles/hjsd763hshj762hshj287.../

The obfuscated URLs are long and error prone (not to mention a pain) to be entered manually. To combat this, the profile URL displays a QR code that can be scanned by a mobile device.

OK, back to Joe. The administrator could either visit the link himself and print out the QR code for Joe, or securely send Joe the link to visit himself.

Once Joe has the QR code (and has installed the OpenVPN app for either Android or iOS), can scan the QR code with his mobile device and download the profile which will be automatically imported into the app.

Note that once a profile has been downloaded, it will automatically be deleted from the OpenVPN web server by an hourly cron job.

Lastly, if Joe misplaces his mobile device the certificate can be revoked:

$ source /etc/openvpn/easy-rsa/vars
$ /etc/openvpn/easy-rsa/revoke-full joe-mobile