ssm-tunnel-updown.dns-example

#!/bin/bash -e

# Simple up-down script that can set DNS servers for domains
# resolvable over the SSM Tunnel link.
# For example if you have a Private VPC Route53 zone you can
# make it resolvable by your laptop with this script.

# Requires 'update-systemd-resolved' in $PATH. Download it from
# https://github.com/jonathanio/update-systemd-resolved

# It is called with these parameters:
#   {status} {device-name} {local-ip} {remote-ip} [{route} ...]
# Where {status} will be: 'up' or 'down'.

## Update these two variables to your needs

DNS_SERVERS="172.31.0.2"
DNS_DOMAINS="example.com vpc-only.example.com"

## Nothing to configure below here

if [ "$1" != "up" ]; then
    # Only handle 'up' events. The config will be auto-cleared
    # when the interface goes down.
    exit 0
fi

# Set OpenVPN-style variables
export script_type="up"
export dev="$2"

# Build the foreign_option_X variables
IDX=1
for DNS_SERVER in ${DNS_SERVERS}; do
    export foreign_option_${IDX}="dhcp-option DNS ${DNS_SERVER}"
    IDX=$((IDX + 1))
done

for DNS_DOMAIN in ${DNS_DOMAINS}; do
    export foreign_option_${IDX}="dhcp-option DOMAIN-ROUTE ${DNS_DOMAIN}"
    IDX=$((IDX + 1))
done

exec update-systemd-resolved