#vpn gateway

Recently, we had an usecase where we need to route certain traffic from  the machines in VPC public subnet through VPN gateway.It took quite a bit of time to understand how to do this as AWS VPC documentation doesn't specify much about selective routing in Public Subnet instead use cases of using either internet gateway or vpn gateway on subnets.

Once you have a successful VPN Gateway established and attached to your AWS VPC, you can just add traffic that you want to route through VPN Gateway by adding specific routes in the Routing Table of your public subnet.

Lets say you want to route traffic to specific ip address like 122.64.64.65, 122.64.64.66, 122.61.64.78, 122.64.62.79 through your VPN gateway then you can just add these routes to the routing table and select your VPN gateway for it. Also if you know the CIDR of your network (192.168.10.1/16) outside VPC then can just route traffic to that network through VPN gateway and let the rest of the traffic flow through Internet Gateway.

So entries in your public subnet routing table will look like :

10.0.0.0/24 ==> Local  (Traffic within your VPC subnets) 0.0.0.0/0 ==> igw-xxxxxxxx  (Rest of the traffic over Internet gateway) 192.168.10.1/16 ==> vgw-xxxxxxxx (Specific traffic to VPN gateway)