dnsbl-exporter - The DNS Block List Exporter

This is a server (aka Prometheus-compatible exporter) which checks the configured hosts against various DNSBL (DNS Block Lists), sometimes referred to as RBLs.

Should you accept this mission, your task is to scrape /metrics using Prometheus to create graphs, alerts, and so on.

This is (still) pretty early software. But I happily accept all kinds of feedback - bug reports, PRs, code, docs, ... :)

Using

Configuration

See rbls.ini and targets.ini files in this repository. The files follow the Nagios format as this exporter is meant to be a drop-in replacement so you can factor out Nagios, one (simple) step at a time. :-)

Otherwise:

$ dnsbl-exporter -h
...
--config.dns-resolver value  IP address of the resolver to use. (default: "127.0.0.1:53")
--config.rbls value          Configuration file which contains RBLs (default: "./rbls.ini")
--config.targets value       Configuration file which contains the targets to check. (default: "./targets.ini")
--config.domain-based        RBLS are domain instead of IP based blocklists (default: false)
--web.listen-address value   Address to listen on for web interface and telemetry. (default: ":9211")
--web.telemetry-path value   Path under which to expose metrics. (default: "/metrics")
--log.debug                  Enable more output in the logs, otherwise INFO.
--log.output value           Destination of our logs: stdout, stderr (default: "stdout")
--help, -h                   show help
--version, -V                Print the version information.

Running

1. Go to release and grab a release for your platform.
2. Get rbls.ini and put it next to the binary.
3. Get targets.ini, and customize. Or use the defaults.
4. ./dnsbl-exporter

Go to http://127.0.0.1:9211/ in your browser.

Container

Docker/OCI images are available in the container registry:

$ docker pull ghcr.io/luzilla/dnsbl_exporter:vX.Y.Z
...

Please note: latest is not provided.

The images expect target.ini and rbls.ini in the following location:

/

Either start the container and supply the contents, or build your own image:

docker run \
    --rm \
    -e DNSBL_EXP_RESOLVER=your.resolver:53 \
    -p 9211:9211 \
    -v ./conf:/etc/dnsbl-exporter \
    ghcr.io/luzilla/dnsbl_exporter:vA.B.C

FROM ghcr.io/luzilla/dnsbl_exporter:vA.B.C

ADD my-target.ini /target.ini
ADD my-rbls.ini /rbls.ini

Helm

Additionally, a helm chart is provided to run the exporter on Kubernetes.

To get started quickly, an unbound container is installed into the pod alongside the exporter. This unbound acts as a local DNS server to send queries to. You may turn this off with unbound.enabled=false and provide your own resolver (via config.resolver: an.ip.address:port).

To configure the chart, copy chart/values.yaml to values.local.yaml and edit the file; for example, to turn off the included unbound and to supply your own resolver, set your own images and last but not least: supply your own targets and RBLs.

The sources for the helm chart are in chart, to install it, you can inspect the Chart.yaml for the version, check the helm chart repository or check out artifact hub.

The following command creates a dnsbl-exporter release which is installed into a namespace called my-namespace:

helm upgrade --install \
    --namespace my-namespace \
    -f ./chart/values.yaml \
    -f ./values.local.yaml \
    dnsbl-exporter oci://ghcr.io/luzilla/charts/dnsbl-exporter --version 0.1.0

Querying

The individual configured servers and their status are represented by a gauge:

luzilla_rbls_ips_blacklisted{hostname="mail.gmx.net",ip="212.227.17.168",rbl="ix.dnsbl.manitu.net"} 0

This represent the server's hostname and the DNSBL in question. 0 (zero) for unlisted and 1 (one) for listed. Requests to the DNSBL happen in real-time and are not cached. Take this into account and use accordingly.

If the exporter is configured for DNS based blocklists, the ip label represents the return code of the blocklist.

If you happen to be listed — inspect the exporter's logs as they will contain a reason.

Alerting

The following example alerts use the scraped metrics from this exporter.

prometheus

alerts:
  groups:
  - name: dnsbl-exporter
    rules:
    - alert: DnsblRblListed
      expr: luzilla_rbls_ips_blacklisted > 0
      for: 15m
      labels:
        severity: critical
      annotations:
        description: Domain {{ $labels.hostname }} ({{ $labels.ip }}) listed at {{ $labels.rbl }}
        summary: Domain listed at RBL
        runbook_url: https://example.org/wiki/runbooks

For more details, see the Prometheus documentation.

Prometheus Operator

apiVersion: monitoring.coreos.com/v1
kind: PrometheusRule
metadata:
  name: dnsbl-rules
spec:
  groups:
  - name: dnsbl
    rules:
      - alert: DnsblRblListed
        expr: luzilla_rbls_ips_blacklisted > 0
        for: 15m
        labels:
          severity: critical
        annotations:
          description: '{{ $labels.hostname }} ({{ $labels.ip }}) has been blacklisted in {{ $labels.rbl }} for more than 15 minutes.'
          summary: 'Endpoint {{ $labels.hostname }} is blacklisted'

For more details, see the Prometheus Operator documentation.

Caveat

In order to use the exporter, a proper DNS resolver is needed. Proper means: not Google, not Cloudflare, nor OpenDNS or Quad9 etc.. Instead use a resolver like Unbound and turn off forwarding.

To test on OSX, follow these steps:

$ brew install unbound
...
$ sudo unbound -d -vvvv

(And leave the Terminal open — there will be ample queries and data for you to see and learn from.)

An alternative to Homebrew is to use Docker; an example image is provided in this repository, it contains a working configuration — ymmv.

docker run -p 53:5353/udp ghcr.io/luzilla/unbound:v0.7.0-rc3

Verify Unbound is working and resolution is working:

 $ dig +short @127.0.0.1 spamhaus.org
192.42.118.104

Use /etc/resolv.conf

Use system as a value and the exporter will pick the first resolver from /etc/resolv.conf.

Adequate permissions need to be set by yourself so the exporter can read the file.

• --config.dns-resolver=system
• DNSBL_EXP_RESOLVER=system

License / Author

This code is Apache 2.0 licensed.

For questions, comments or anything else, please get in touch.

Releasing

(This is for myself, since I tend to forget things.)

1. git tag -a x.y.z
2. git push --tags
3. GitHub Actions/GoReleaser will build a pretty release