pptpd

The Point-to-Point Tunneling Protocol is a method for implementing virtual private networks. PPTP uses a control channel over TCP and a GRE tunnel operating to encapsulate PPP packets.

docker-compose.yml

pptpd:
  image: vimagick/pptpd
  volumes:
    - ./pptpd.conf:/etc/pptpd.conf
    - ./pptpd-options:/etc/ppp/pptpd-options
    - ./chap-secrets:/etc/ppp/chap-secrets
  privileged: true
  restart: always

server

$ modprobe nf_conntrack_pptp nf_nat_pptp
$ docker-compose up -d

You need to config firewall:

To let PPTP tunnel maintenance traffic, allow port 1723/tcp.
To let PPTP tunneled data to pass through router, allow proto gre.
Set net.ipv4.ip_forward=1
Set DEFAULT_FORWARD_POLICY=ACCEPT