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A dockerized DNS server and load balancer with automatic discovery

dalidock is a container providing the following services:

  • DNS server, using dnsmasq
  • HTTP and TCP load balancer, using haproxy
  • service discovery, using the dalidock daemon

Services can be discovered from:

  • docker containers
  • libvirt virtual machines

Table of Contents

Usage

Run the container

dalidock can be configured using environment variables:

Variable Default Description
DNS_WILDCARD false Enable DNS wildcard records by default
DNS_DOMAIN local Domain to append to DNS records to register
LB_DOMAIN local Domain to append to reverse-proxy DNS records to register
USE_AD_BLOCKER false Override hosts using https://github.com/StevenBlack/hosts
DOCKER_SOCKET unix:///var/run/docker.sock Docker daemon socket
LIBVIRT_SOCKET /var/run/libvirt/libvirt-sock Libvirt daemon socket
LIBVIRT_IP_TIMEOUT 30.0 Timeout for dalidock to detect a VM's IP address
UPSTREAM_NAMESERVER none Nameserver to use when NetworkManager config is empty 
docker run \
    --detach \
    --name dalidock \
    --hostname dalidock \
    --restart=unless-stopped \
    --net bridge \
    --log-opt max-size=50m \
    --log-opt max-file=3 \
    --volume /var/run/docker.sock:/var/run/docker.sock:ro \
    --cap-add NET_ADMIN \
    --publish 172.17.0.1:53:53/udp \
    --publish 80:80 \
    --env DNS_DOMAIN=my.local.env \
    --env LB_DOMAIN=my.local.env \
    lionelnicolas/dalidock

Make your host uses dalidock as a DNS server

If your system uses NetworkManager, /etc/resolv.conf is probably a symlink pointing to a file generated by NetworkManager. So you'll first need to remove that symlink and recreate /etc/resolv.conf. Then replace its content with:

search my.local.env
domain my.local.env
nameserver 172.17.0.1

Uses NetworkManager's data for upstream DNS servers

If your system uses NetworkManager, /run/NetworkManager/resolv.conf contains the DNS server addresses got from network configuration (DHCP, manual ...)

dalidock can handle wifi/ethernet/VPN connection switches by watching this file, and tell dnsmasq to reload and use "new" upstream servers.

If you want to use that feature, you'll just need to map this directory when starting the dalidock container:

    --volume /run/NetworkManager:/run/NetworkManager:ro

Custom SSL certificates

Embedded haproxy load balancer is loading SSL certificates from /run/haproxy/certs. If that directory is empty or non-existing, the container's entrypoint will generate a self-signed one to make haproxy able to listen on SSL.

If you want to use your own certificates, you could map that directory like:

    --volume /opt/ssl/pems:/run/haproxy/certs

Files contained in that directory must be in the PEM format.

See https://www.haproxy.com/blog/haproxy-ssl-termination/ for more information.

Supported labels

dalidock use labels to configure DNS and load balancing.

Label Value format Description
dns.wildcard true, false Enable wildcard for created DNS records
dns.domain my.domain Override domain to append to created DNS records
dns.aliases server-alias1,other-hostname Add DNS aliases to created hostname DNS record
lb.domain my.loadbalanced.domain Override domain to append to load-balancer DNS records
lb.http ${HOSTNAME}:${BACKEND_PORT} Add HTTP reverse-proxy entry to haproxy
lb.tcp ${HOSTNAME}:${FRONTEND_PORT}:${BACKEND_PORT} Add TCP frontend entry to haproxy

See examples below for more explanations.

Register containers

Default values

when starting a new container, both name and hostname will be registered in the DNS. So if you start a container using:

docker run \
    -it \
    --name qwerty \
    --hostname asdfgh \
    ubuntu

Then, the following DNS records will be available:

qwerty.                   0   IN   A   172.17.0.7
asdfgh.                   0   IN   A   172.17.0.7
qwerty.my.local.env.      0   IN   A   172.17.0.7
asdfgh.my.local.env.      0   IN   A   172.17.0.7
7.0.17.172.in-addr.arpa.  0   IN   PTR asdfgh.my.local.env.

Override DNS domain

docker run \
    -it \
    --name qwerty \
    --hostname asdfgh \
    --label dns.domain=other.fqdn \
    ubuntu

Then, the following DNS records will be available:

qwerty.                   0   IN   A   172.17.0.7
asdfgh.                   0   IN   A   172.17.0.7
qwerty.other.fqdn.        0   IN   A   172.17.0.7
asdfgh.other.fqdn.        0   IN   A   172.17.0.7
7.0.17.172.in-addr.arpa.  0   IN   PTR asdfgh.other.fqdn.

Add DNS aliases

docker run \
    -it \
    --name qwerty \
    --hostname asdfgh \
    --label dns.domain=other.fqdn \
    --label dns.aliases=alias1,alias2,otheralias \
    ubuntu

Then, the following DNS records will be available:

qwerty.                   0   IN   A   172.17.0.7
asdfgh.                   0   IN   A   172.17.0.7
alias1.                   0   IN   A   172.17.0.7
alias2.                   0   IN   A   172.17.0.7
otheralias.               0   IN   A   172.17.0.7
qwerty.other.fqdn.        0   IN   A   172.17.0.7
asdfgh.other.fqdn.        0   IN   A   172.17.0.7
alias1.other.fqdn.        0   IN   A   172.17.0.7
alias2.other.fqdn.        0   IN   A   172.17.0.7
otheralias.other.fqdn.    0   IN   A   172.17.0.7
7.0.17.172.in-addr.arpa.  0   IN   PTR asdfgh.other.fqdn.

Enable wildcard DNS

docker run \
    -it \
    --name qwerty \
    --hostname asdfgh \
    --label dns.wildcard=true \
    ubuntu

Then, the following DNS records will be available:

qwerty.                   0   IN   A   172.17.0.7
asdfgh.                   0   IN   A   172.17.0.7
*.qwerty.                 0   IN   A   172.17.0.7
*.asdfgh.                 0   IN   A   172.17.0.7
qwerty.my.local.env.      0   IN   A   172.17.0.7
asdfgh.my.local.env.      0   IN   A   172.17.0.7
*.qwerty.my.local.env.    0   IN   A   172.17.0.7
*.asdfgh.my.local.env.    0   IN   A   172.17.0.7
7.0.17.172.in-addr.arpa.  0   IN   PTR asdfgh.my.local.env.

Add an HTTP reverse-proxy entry in haproxy

docker run \
    -it \
    --name tomcat-server \
    --hostname tomcat-server \
    --label lb.http=tomcat:8080 \
    tomcat:8.0

This will create an haproxy frontend matching http://tomcat.*, and redirect traffic to port 8080 of the tomcat-server container.

Then, the following DNS records will be available:

tomcat-server.              0   IN   A   172.17.0.7
tomcat-server.my.local.env. 0   IN   A   172.17.0.7
tomcat.                     0   IN   A   172.17.0.2
tomcat.my.local.env.        0   IN   A   172.17.0.2
7.0.17.172.in-addr.arpa.    0   IN   PTR tomcat-server.my.local.env.

If you start another container with label lb.http=tomcat:8080, traffic will be balanced to both containers (dalidock will simply add the new container to the existing haproxy backend).

lb.http label can take comma-separated list of HOST:PORT.

Add an HTTP reverse-proxy entry in haproxy (and override DNS domain)

docker run \
    -it \
    --name tomcat-server \
    --hostname tomcat-server \
    --label lb.http=tomcat:8080 \
    --label lb.domain=frontend.srv \
    tomcat:8.0

This will create an haproxy frontend matching http://tomcat.*, and redirect traffic to port 8080 of the tomcat-server container.

Then, the following DNS records will be available:

tomcat-server.              0   IN   A   172.17.0.7
tomcat-server.my.local.env. 0   IN   A   172.17.0.7
tomcat.                     0   IN   A   172.17.0.2
tomcat.frontend.srv.        0   IN   A   172.17.0.2
7.0.17.172.in-addr.arpa.    0   IN   PTR tomcat-server.my.local.env.

lb.http label can take comma-separated list of HOST:PORT.

Add a TCP frontend in haproxy

docker run \
    -it \
    --name redis-server \
    --hostname redis-server \
    --label lb.tcp=redis:1234:6379 \
    --label lb.domain=data.srv \
    redis

This will create a TCP haproxy frontend listening on port 1234, and redirect traffic to port 6379 of the redis-server container.

Then, the following DNS records will be available:

redis-server.               0   IN   A   172.17.0.7
redis-server.my.local.env.  0   IN   A   172.17.0.7
redis.                      0   IN   A   172.17.0.2
redis.data.srv.             0   IN   A   172.17.0.2
7.0.17.172.in-addr.arpa.    0   IN   PTR redis-server.my.local.env.

If you start another container with label lb.tcp=redis:1234:6379, traffic will be balanced to both containers (dalidock will simply add the new container to the existing haproxy backend).

lb.tcp label can take comma-separated list of HOST:FRONTEND_PORT:BACKEND_PORT.

Register libvirt-based virtual machines

Prerequisites

You'll need to ensure that dalidock has access to the libvirt daemon socket, by adding that volume mapping when starting the container:

--volume /var/run/libvirt:/var/run/libvirt:ro

IP address detection

dalidock will try to detect the VM's IP address when the Started event is detected. If no IP address is found after LIBVIRT_IP_TIMEOUT, then the VM will be ignored.

Please note that this detection will only work if either:

  1. VM primary network interface is configured as DHCP, and is using libvirt-managed DHCP server (dnsmasq)
  2. Qemu guest agent is enabled in libvirt, and running in the VM

As soon as the IP address is detected, the following DNS record will be available:

${VM_NAME}.${DNS_DOMAIN}.   0   IN   A   ${VM_IP_ADDRESS}

Labels

Libvirt doesn't have labels, so dalidock use metadata instead, which needs to be set in the virtual machine XML description. This can be achieved by editing the XML with virsh edit my-vm-to-discover, or by using the virsh metadata command:

With libvirt, dalidock works using the same labels as for containers.

For example, to enable wildcard DNS on a virtual machine, you can use:

virsh metadata my-vm-to-discover \
	--config \
	--uri http://github.com/lionelnicolas/dalidock \
	--key dalidock \
	--set '<labels dns.wildcard="true"/>'

Or to add reverse-proxy entries:

virsh metadata my-vm-to-discover \
	--config \
	--uri http://github.com/lionelnicolas/dalidock \
	--key dalidock \
	--set '<labels lb.http="tomcat:8080" lb.domain="frontend.srv"/>'

Build

In order to build this container image instead of using the one on the Docker Hub, you can use the following command from the root directory of this repository:

docker build -t lionelnicolas/dalidock .

License

This is licensed under the Apache License, Version 2.0. Please see LICENSE for the full license text.

Copyright 2016-2020 Lionel Nicolas