Short guide on how to set up a Docker container as a DHCP server

docker-dhcpd.md

Setting up a Docker container as a DHCP server

In this guide I’ve tested a number of different commands and configurations using Docker to run a container with dhcpd (+macvlan driver) to serve my clients in my home network. In the end i’ll migrate from my Windows 2012 R2 Server running DHCP to a much more lightweight Docker container (7.42 MB in total). Wow.

My home environment:

• Firewall (Juniper)
  • I’m running IP helper for bootp which in this case means that i relay DHCP requests from various VLANs into one where i've placed my Windows 2012 R2 server. This is also where my container will live. See the FW configuration below:

forwarding-options {
	helpers {
		bootp {
			description "Global DHCP relay service";
			server 10.0.99.6;
			maximum-hop-count 4;
			interface {
				ge-0/0/x.XX;
				ge-0/0/x.XX;
			}
		}
	}
}

• ESXi v6.5
  • Running a VM (Debian Jessie) where I’ve installed Docker. The VM have two network interfaces assigned to it, one in a “DMZ” zone and one which I will trunk all VLANs to via ESXi and a port group with VLAN id 4095 (trunk all VLANs).
  • On the port group that will be used for trunking VLANs i had to enable Promiscuous mode via the Security-settings.

Dockerfile

FROM alpine:latest
RUN set -xe \
	&& apk add --update --no-progress dhcp \
	&& rm -rf /var/cache/apk/*
RUN ["touch", "/var/lib/dhcp/dhcpd.leases"]
CMD ["/usr/sbin/dhcpd", "-4", "-f", "-d", "--no-pid", "-cf", "/etc/dhcp/dhcpd.conf"]

docker-compose.yml

version: '3'

services:
    dhcpd:
        build: .
        restart: unless-stopped
        networks:
            internal_network:
                ipv4_address: 10.0.99.6

        volumes:
            - ./dhcpd.conf:/etc/dhcp/dhcpd.conf

networks:
    internal_network:
        external:
            name: macvlan0

Configuring Docker and running container

1. Create a VLAN interface on the Docker host and give it an address in the subnet

iface ens192.99 inet static
  address 10.0.99.5
  netmask 255.255.255.0

2. Create a network using the macvlan driver.

docker network create -d macvlan --subnet=10.0.99.0/24 --gateway=10.0.99.1 -o parent=ens192.30 macvlan0

3. Here's the Docker container repo: docker-dhcpd
4. My dhcpd.conf that have worked for me, remember that i'm using a DHCP relay between the client and server

authoritative;

default-lease-time 86400;
max-lease-time 86400;

# This is a workaround to let this dhcpd server serve requests to other subnets
# then it's own.
# If this is not present then the dhcpd daemon will throw an error and exit.
subnet 10.0.99.0 netmask 255.255.255.0 {
}

# This is my WLAN subnet
subnet 10.0.100.0 netmask 255.255.255.0 {
	option routers 10.0.100.1;
	option subnet-mask 255.255.255.0;
	range 10.0.100.150 10.0.100.200;
	option broadcast-address 10.0.100.255;
	option domain-name-servers 8.8.8.8, 8.8.4.4;
}

5. Build the Docker image (from within project directory)

docker build . -t dhcpd

6. Run the container

docker run -d --restart unless-stopped --ip 10.0.99.6 --net=macvlan0 dhcpd

or simply

docker-compose up -d

7. Copy the dhcpd.lease file from the container to your local filesystem to check if you have any active leases

docker cp <Container ID>:/var/lib/dhcp/dhcpd.leases .