coredns/plugin/dnstap/README.md

dnstap

Name

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] {
  [identity IDENTITY]
  [version VERSION]
}

• 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.

Examples

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

dnstap /tmp/dnstap.sock

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
}

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 {
        if tapPlugin, ok := taph.(dnstap.Dnstap); ok {
            x.tapPlugins = append(x.tapPlugins, &tapPlugin)
        }
    }
    return nil
})

And then in your plugin:

import (
  github.com/coredns/coredns/plugin/dnstap/msg
  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)
        tapPlugin.TapMessage(q)
    }
    // ...
}

See Also

The website dnstap.info has info on the dnstap protocol. The forward plugin's dnstap.go uses dnstap to tap messages sent to an upstream.