Start OpenVPN inside network namespace

vpnns_up.sh

#!/bin/bash
sudo ip netns add vpn
sudo ip netns exec vpn ip addr add 127.0.0.1/8 dev lo
sudo ip netns exec vpn ip link set lo up
sudo ip link add vpn0 type veth peer name vpn1
sudo ip link set vpn0 up
sudo ip link set vpn1 netns vpn up
sudo ip addr add 10.10.10.1/24 dev vpn0
sudo ip netns exec vpn ip addr add 10.10.10.2/24 dev vpn1
sudo ip netns exec vpn ip route add 37.59.63.23 via 10.10.10.1 dev vpn1
sudo ip netns exec vpn ip route add default via 10.10.10.254 dev vpn1 
sudo iptables -A INPUT ! -i vpn0 -s 10.10.10.0/24 -j DROP
sudo iptables -t nat -A POSTROUTING -s 10.10.10.0/24 -o en+ -j MASQUERADE
sudo sysctl  -q net.ipv4.ip_forward=1
sudo mkdir  -p /etc/netns/vpn
echo "nameserver 8.8.8.8" |sudo tee /etc/netns/vpn/resolv.conf
sudo ip netns exec vpn /usr/sbin/openvpn --daemon --writepid /run/openvpn/vpn.pid --cd /etc/openvpn/ --config vpn.conf