donutdns

Block online ads by intercepting DNS queries

Project Overview

The github.com/shoenig/donutdns module provides a CoreDNS plugin as well as a standalone executable DNS server that can be used to block DNS queries to domains used by online advertisers, trackers, scammers, and crypto miners. The project is meant to be a simpler alternative to the venerable Pi-Hole. In particular, donutdns is easy to run as a non-root Docker container with little to no configuration.

sample logs

[INFO] plugin/donutdns: BLOCK query (A) for www.google-analytics.com.
[INFO] plugin/donutdns: BLOCK query (A) for www-google-analytics.l.google.com.
[INFO] plugin/donutdns: BLOCK query (AAAA) for stats.wp.com.
[INFO] plugin/donutdns: BLOCK query (A) for www.googletagservices.com.
[INFO] plugin/donutdns: BLOCK query (A) for tpc.googlesyndication.com.
[INFO] plugin/donutdns: BLOCK query (A) for c.amazon-adsystem.com.
[INFO] plugin/donutdns: BLOCK query (AAAA) for static.ads-twitter.com.

Domain Block/Allow Lists

The default set of blocked domains are retrieved from the source lists in sources.json. These lists are compiled and maintained by volunteers; see their respective headers for more information about terms of use and other metadata. Thank you to those who contribute to these domain block lists.

The blocking of the default set of domains can be disabled by setting DONUT_DNS_NO_DEFAULT=1.

Additional domains can be blocked by donutdns by setting any of the DONUT_DNS_BLOCK, DONUT_DNS_BLOCK_FILE, DONUT_DNS_BLOCK_DIR environment variables.

Likewise, domains can be explicitly allowed by setting the DONUT_DNS_ALLOW, DONUT_DNS_ALLOW_FILE, DONUT_DNS_ALLOW_DIR environment variables. The allow lists take precedense over the block lists.

For nasty companies like Facebook with dynamic subdomains, donutdns supports blocking domains by suffix matching. By setting any of the DONUT_DNS_SUFFIX, DONUT_DNS_SUFFIX_FILE, DONUT_DNS_SUFFIX_DIR any query matching the given suffix(es) will be blocked.

Getting Started

donutdns can be used as a CoreDNS Plugin or standalone DNS Server.

Install

The donutdns standalone DNS Server is written in Go.

Pre-compiled binaries are available for download from the Releases page.

Docker images are available from Docker Hub.

With the Go toolchain, donutdns standalone can be compiled and installed in one step:

go install github.com/shoenig/donutdns@latest

DNS Server

The donutdns executable uses environment variables for configuration.

Environment Variable	Description	Default
DONUT_DNS_PORT	The port to listen on	5301
DONUT_DNS_NO_DEBUG	Disable CoreDNS debug logging	unset
DONUT_DNS_NO_LOG	Disable CoreDNS logging	unset
DONUT_DNS_ALLOW	Comma separated list of domains to NOT block	unset
DONUT_DNS_ALLOW_FILE	File with list of domains to NOT block	unset
DONUT_DNS_ALLOW_DIR	Directory with one or more files of list of domains to NOT block	unset
DONUT_DNS_BLOCK	Comma separated list of domains to block	unset
DONUT_DNS_BLOCK_FILE	File with list of domains to block	unset
DONUT_DNS_BLOCK_DIR	Directory with one or more files of list of domains to block	unset
DONUT_DNS_SUFFIX	Comma separated list of domains to block by suffix	unset
DONUT_DNS_SUFFIX_FILE	File with list of domains to block by suffix	unset
DONUT_DNS_SUFFIX_DIR	Directory with one or more files of list of domains to block by suffix	unset
DONUT_DNS_NO_DEFAULTS	Disable blocking of default domain block lists	unset
DONUT_DNS_UPSTREAM_1	Fallback DNS Server for non-blocked queries	1.1.1.1
DONUT_DNS_UPSTREAM_2	Fallback DNS Server for non-blocked queries	1.0.0.1
DONUT_DNS_UPSTREAM_NAME	Fallback DNS Server TLS name	cloudflare-dns.com

CoreDNS Plugin

The donutdns CoreDNS plugin is configured using the donutdns block in a standard CoreConfig configuration file.

Minimal donutdns plugin configuration. defaults can be set to true or false to enable or disable the use of default domain block lists.

donutdns {
  defaults true
}

This configuration uses block_file to explicitly block a set of domains listed in a file on local disk.

donutdns {
  defaults false
  block_file /etc/blocked-domains.txt
}

This configuration uses block and allow to explicitly block and allow certain domains.

donutdns {
  defaults true
  block facebook.com,www.facebook.com,m.facebook.com,fb.com
  allow example.com
}

When using donutdns as a CoreDNS plugin, the fallthrough behavior must be configured as desired using one or more other plugins. To recreate the same recursive behavior as the standalone executable, use the forward plugin.

forward . 1.1.1.1 1.0.0.1 {
  tls_servername cloudflare-dns.com
}

Custom block file

The file format for block_file or DONUT_DNS_BLOCK_FILE is simply a newline delimited list of domains. Empty lines and lines beginning with # are always ignored. All other lines are scanned with a regular expression to find the first plausible domain name in the line. social-media.list contains an example file for blocking facebook, instagram, and whatsapp.

# An example block list
example.com
www.example.com

Subcommands

check

Use the check command to simulate whether a DNS query would be blocked or allowed.

Usage: donutdns check [-quiet] [-defaults] <domain>

-quiet will suppress verbose debug logging output

-defaults will activate the built-in block lists (which is slow)

Run

as an executable

With no configuration, donutdns will use the built-in domain block lists by default.

$ donutdns

Use the environment variables described above to configure things.

$ DONUT_DNS_PORT=5533 DONUT_DNS_NO_DEBUG=1 donutdns

as a systemd unit

The donutdns.service file provides an example Systemd Service Unit file for running donutdns via systemd.

● donutdns.service - Block ads, trackers, and malicioius sites using DonutDNS.
     Loaded: loaded (/etc/systemd/system/donutdns.service; enabled; preset: enabled)
     Active: active (running) since Sun 2023-02-12 05:09:45 UTC; 13s ago
   Main PID: 8117 (donutdns)
      Tasks: 17 (limit: 18269)
     Memory: 36.1M (max: 42.0M available: 5.8M)
        CPU: 1.428s
     CGroup: /system.slice/donutdns.service
             └─8117 /opt/bin/donutdns

# A minimal unit file, see donutdns.service for more.

[Unit]
Description=Block ads, trackers, and malicioius sites using DonutDNS.

[Service]
Type=simple
User=nobody
ExecStart=/opt/bin/donutdns
Environment=DONUT_DNS_PORT=53
Environment=DONUT_DNS_SUFFIX_DIR=/etc/blocklists.d
MemoryMax=128M
CPUWeight=90

[Install]
WantedBy=multi-user.target

Typically this file would be created at /etc/systemd/system/donutdns.service.

Configure systemd to run the new service.

sudo systemctl daemon-reload           # update systemd configurations
sudo systemctl enable donutdns.service # enable donutdns service in systemd
sudo systemctl start donutdns          # start donutdns service in systemd
sudo systemctl status donutdns         # inspect status of donutdns service in systemd

bind to port 53

When running as non-root user, we must set CAP_NET_BIND on the donutdns binary.

sudo setcap CAP_NET_BIND_service+eip /opt/bin/donutdns

as a docker container

donutdns is available from Docker Hub

This will run the donutdns Docker container as the nobody user, mapping traffic from port 53.

docker run --rm -p 53:5301 -u nobody shoenig/donutdns:v0.3.2

as a Nomad job

using docker driver

job "donutdns" {
  datacenters = ["dc1"]

  group "donut" {
    network {
      mode = "bridge"
      port "dns" {
        static       = 53
        to           = 5301
        host_network = "public"
      }
    }

    task "dns" {
      driver = "docker"
      user   = "nobody"

      resources {
        cpu    = 120
        memory = 64
        disk   = 128
      }

      env {
        DONUT_DNS_NO_DEBUG   = 1
        DONUT_DNS_BLOCK_FILE = "/local/blocks.txt"
      }

      config {
        image = "shoenig/donutdns:v0.3.2"
      }

      template {
        destination = "local/blocks.txt"
        change_mode = "restart"
        perms       = "644"
        data        = <<EOH
# [example]
example.com
www.example.com
EOH
      }
    }
  }
}

Troubleshooting

Certain systems (looking at you RHEL/CentOS) make running a useable DNS server particularly difficult. On my homelab CentOS 9 system I had to disable ipv6 at the kernel level, disable SELinux, and disable firewalld. You may need to do something similar (ideally updating rules rather than disabling things) on your system.

ubuntu 22.04

Need to disable systemd-resolved first, which binds to :53 out of the box.

sudo systemctl disable systemd-resolved
sudo systemctl stop systemd-resolved

Contributing

The github.com/shoenig/donutdns module is always improving with new features and bug fixes. For contributing such bug fixes and new features please file an issue.

License

The github.com/shoenig/donutdns module is open source under the BSD-3-Clause license.