dnstap

Source

dnstap enables logging to dnstap.

Description

dnstap is a flexible, structured binary log format for DNS software; see https://dnstap.info. With this plugin you make CoreDNS output dnstap logging.

Every message is sent to the socket as soon as it comes in, the dnstap plugin has a buffer of 10000 messages, above that number dnstap messages will be dropped (this is logged).

Syntax

dnstap SOCKET [full] [writebuffer] [queue] {
  [identity IDENTITY]
  [version VERSION]
  [extra EXTRA]
  [skipverify]
}

SOCKET is the socket (path) supplied to the dnstap command line tool.
full to include the wire-format DNS message.
IDENTITY to override the identity of the server. Defaults to the hostname.
VERSION to override the version field. Defaults to the CoreDNS version.
EXTRA to define “extra” field in dnstap payload, metadata replacement available here.
skipverify to skip tls verification during connection. Default to be secure

Examples

Log information about client requests and responses to /tmp/dnstap.sock.

dnstap /tmp/dnstap.sock

Log information about client requests and responses and tcp write buffer is 1024Mb and queue is 204810000.

dnstap /tmp/dnstap.sock full 1024 2048

Log information including the wire-format DNS message about client requests and responses to /tmp/dnstap.sock.

dnstap unix:///tmp/dnstap.sock full

Log to a remote endpoint.

dnstap tcp://127.0.0.1:6000 full

Log to a remote endpoint by FQDN.

dnstap tcp://example.com:6000 full

Log to a socket, overriding the default identity and version.

dnstap /tmp/dnstap.sock {
  identity my-dns-server1
  version MyDNSServer-1.2.3
}

Log to a socket, customize the “extra” field in dnstap payload. You may use metadata provided by other plugins in the extra field.

forward . 8.8.8.8
metadata
dnstap /tmp/dnstap.sock {
  extra "upstream: {/forward/upstream}"
}

Log to a remote TLS endpoint.

dnstap tls://127.0.0.1:6000 full {
  skipverify
}

You can use dnstap more than once to define multiple taps. The following logs information including the wire-format DNS message about client requests and responses to /tmp/dnstap.sock, and also sends client requests and responses without wire-format DNS messages to a remote FQDN.

dnstap /tmp/dnstap.sock full
dnstap tcp://example.com:6000

Command Line Tool

Dnstap has a command line tool that can be used to inspect the logging. The tool can be found at GitHub: https://github.com/dnstap/golang-dnstap. It’s written in Go.

The following command listens on the given socket and decodes messages to stdout.

$ dnstap -u /tmp/dnstap.sock

The following command listens on the given socket and saves message payloads to a binary dnstap-format log file.

$ dnstap -u /tmp/dnstap.sock -w /tmp/test.dnstap

Listen for dnstap messages on port 6000.

$ dnstap -l 127.0.0.1:6000

Using Dnstap in your plugin

In your setup function, collect and store a list of all dnstap plugins loaded in the config:

x :=  &ExamplePlugin{}

c.OnStartup(func() error {
    if taph := dnsserver.GetConfig(c).Handler("dnstap"); taph != nil {
        for tapPlugin, ok := taph.(*dnstap.Dnstap); ok; tapPlugin, ok = tapPlugin.Next.(*dnstap.Dnstap) {
            x.tapPlugins = append(x.tapPlugins, tapPlugin)
        }
    }
    return nil
})

And then in your plugin:

import (
  "github.com/coredns/coredns/plugin/dnstap/msg"
  "github.com/coredns/coredns/request"

  tap "github.com/dnstap/golang-dnstap"
)

func (x ExamplePlugin) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
    for _, tapPlugin := range x.tapPlugins {
        q := new(msg.Msg)
        msg.SetQueryTime(q, time.Now())
        msg.SetQueryAddress(q, w.RemoteAddr())
        if tapPlugin.IncludeRawMessage {
            buf, _ := r.Pack() // r has been seen packed/unpacked before, this should not fail
            q.QueryMessage = buf
        }
        msg.SetType(q, tap.Message_CLIENT_QUERY)
        
        // if no metadata interpretation is needed, just send the message
        tapPlugin.TapMessage(q)

        // OR: to interpret the metadata in "extra" field, give more context info
        tapPlugin.TapMessageWithMetadata(ctx, q, request.Request{W: w, Req: query})
    }
    // ...
}