So this is how I made it work! First of all, I moved to work with Bind instead of Unbound ( inspired by this video here
Bind Server config
//
// named.conf
//
// Provided by Red Hat bind package to configure the ISC BIND named(8) DNS
// server as a caching only nameserver (as a localhost DNS resolver only).
//
// See /usr/share/doc/bind*/sample/ for example named configuration files.
//
options {
directory "/var/named";
dump-file "/var/named/data/cache_dump.db";
statistics-file "/var/named/data/named_stats.txt";
memstatistics-file "/var/named/data/named_mem_stats.txt";
dnssec-enable no;
dnssec-validation no;
allow-query { any;};
allow-recursion { any;};
forward only;
forwarders { 172.31.0.2; }; # This is my VPC internal DNS Server
};
logging {
channel default_debug {
file "data/named.run";
severity dynamic;
};
};
zone "." IN {
type hint;
file "named.ca";
};
include "/etc/named.rfc1912.zones";
include "/etc/named.root.key";
Now make sure to push to your VPN clients the IP of the DNS server you installed ( in this case its the Bind server )
OpenVPN Server config
port 1194 #- change the port you want
proto udp #- protocol can be tcp or udp
dev tun
tun-mtu 1500
tun-mtu-extra 32
mssfix 1450
ca /etc/openvpn/easy-rsa/2.0/keys/ca.crt
cert /etc/openvpn/easy-rsa/2.0/keys/server.crt
key /etc/openvpn/easy-rsa/2.0/keys/server.key
dh /etc/openvpn/easy-rsa/2.0/keys/dh2048.pem
server 10.8.0.0 255.255.255.0
push "redirect-gateway def1"
push "dhcp-option DNS <IP_OF_SERVER_RUNNING_BOTH_OPENVPN_AND_BIND>" # This line push your DNS server to be used by the VPN clients
keepalive 5 30
comp-lzo
persist-key
persist-tun
status server-tcp.log
verb 3
Apparently, VPN clients running on top of linux need "some help" putting the "new" DNS server into use with the following config (see the last lines in the config, get the scripts from here):
VPN Client config
##############################################
# Client-side OpenVPN 2.0 config file #
# for connecting to multi-client server. #
# #
# This configuration can be used by multiple #
# clients, however each client should have #
# its own cert and key files. #
# #
# On Windows, you might want to rename this #
# file so it has a .ovpn extension #
##############################################
# Specify that we are a client and that we
# will be pulling certain config file directives
# from the server.
client
# Use the same setting as you are using on
# the server.
# On most systems, the VPN will not function
# unless you partially or fully disable
# the firewall for the TUN/TAP interface.
;dev tap
dev tun
# Windows needs the TAP-Win32 adapter name
# from the Network Connections panel
# if you have more than one. On XP SP2,
# you may need to disable the firewall
# for the TAP adapter.
;dev-node MyTap
# Are we connecting to a TCP or
# UDP server? Use the same setting as
# on the server.
;proto tcp
proto udp
# The hostname/IP and port of the server.
# You can have multiple remote entries
# to load balance between the servers.
remote <IP_OF_SERVER_RUNNING_BOTH_OPENVPN_AND_BIND> 1194
;remote my-server-2 1194
# Choose a random host from the remote
# list for load-balancing. Otherwise
# try hosts in the order specified.
;remote-random
# Keep trying indefinitely to resolve the
# host name of the OpenVPN server. Very useful
# on machines which are not permanently connected
# to the internet such as laptops.
resolv-retry infinite
# Most clients don't need to bind to
# a specific local port number.
nobind
# Downgrade privileges after initialization (non-Windows only)
;user nobody
;group nobody
# Try to preserve some state across restarts.
persist-key
persist-tun
# If you are connecting through an
# HTTP proxy to reach the actual OpenVPN
# server, put the proxy server/IP and
# port number here. See the man page
# if your proxy server requires
# authentication.
;http-proxy-retry # retry on connection failures
;http-proxy [proxy server] [proxy port #]
# Wireless networks often produce a lot
# of duplicate packets. Set this flag
# to silence duplicate packet warnings.
;mute-replay-warnings
# SSL/TLS parms.
# See the server config file for more
# description. It's best to use
# a separate .crt/.key file pair
# for each client. A single ca
# file can be used for all clients.
ca /Users/myusername/name_of_my_ca.crt
cert /Users/myusername/name_of_my_client.crt
key /Users/myusername/name_of_my_client.key
# Verify server certificate by checking
# that the certicate has the nsCertType
# field set to "server". This is an
# important precaution to protect against
# a potential attack discussed here:
# http://openvpn.net/howto.html#mitm
#
# To use this feature, you will need to generate
# your server certificates with the nsCertType
# field set to "server". The build-key-server
# script in the easy-rsa folder will do this.
;ns-cert-type server
# If a tls-auth key is used on the server
# then every client must also have the key.
;tls-auth ta.key 1
# Select a cryptographic cipher.
# If the cipher option is used on the server
# then you must also specify it here.
;cipher x
# Enable compression on the VPN link.
# Don't enable this unless it is also
# enabled in the server config file.
comp-lzo
# Set log file verbosity.
verb 3
# Silence repeating messages
;mute 20
# This updates the resolvconf with dns settings
setenv PATH /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
script-security 2
up /etc/openvpn/update-resolv-conf.sh
down /etc/openvpn/update-resolv-conf.sh
down-pre
Now once your VPN server and Bind server are properly set up with the above your VPN clients ( your private mac/office computers on-premise etc ) , while connected to the VPN server, are capable not only to ssh private IPs but also resolve internal AWS hostnames in the VPC e.g ip-172-31-0-63.us-west-1.compute.internal
EDIT:
The following helps to create a single file to setup a VPN client, useful for mobile devices.
All-in-one VPN Client config
client
dev tun
proto udp
remote PUBLIC_IP 1194
tls-version-min 1.2
tls-cipher <CIPHERS>
cipher AES-256-CBC
auth SHA512
resolv-retry infinite
auth-retry none
nobind
persist-key
persist-tun
remote-cert-tls server
comp-lzo
verb 3
tls-client
<ca>
...
</ca>
<cert>
...
</cert>
<key>
...
</key>
<tls-auth>
...
</tls-auth>
