coredns/middleware/kubernetes/handler.go

package kubernetes

import (
	"errors"
	"strings"

	"github.com/coredns/coredns/middleware"
	"github.com/coredns/coredns/middleware/pkg/dnsutil"
	"github.com/coredns/coredns/request"

	"github.com/miekg/dns"
	"golang.org/x/net/context"
)

// ServeDNS implements the middleware.Handler interface.
func (k Kubernetes) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
	state := request.Request{W: w, Req: r}
	if state.QClass() != dns.ClassINET {
		return dns.RcodeServerFailure, middleware.Error(k.Name(), errors.New("can only deal with ClassINET"))
	}

	m := new(dns.Msg)
	m.SetReply(r)
	m.Authoritative, m.RecursionAvailable, m.Compress = true, true, true
	// Check that query matches one of the zones served by this middleware,
	// otherwise delegate to the next in the pipeline.
	zone := middleware.Zones(k.Zones).Matches(state.Name())
	if zone == "" {
		if state.Type() != "PTR" {
			return middleware.NextOrFailure(k.Name(), k.Next, ctx, w, r)
		}
		// If this is a PTR request, and the request is in a defined
		// pod/service cidr range, process the request in this middleware,
		// otherwise pass to next middleware.
		if !k.isRequestInReverseRange(state.Name()) {
			return middleware.NextOrFailure(k.Name(), k.Next, ctx, w, r)
		}
		// Set the zone to this specific request.
		zone = state.Name()
	}
	records, extra, _, err := k.routeRequest(zone, state)

	// Check for Autopath search eligibility
	if k.AutoPath.Enabled && k.IsNameError(err) && (state.QType() == dns.TypeA || state.QType() == dns.TypeAAAA) {
		p := k.findPodWithIP(state.IP())
		for p != nil {
			name, path, ok := splitSearch(zone, state.QName(), p.Namespace)
			if !ok {
				break
			}
			if (dns.CountLabel(name) - 1) < k.AutoPath.NDots {
				break
			}
			origQName := state.QName()
			// Search "svc.cluster.local." and "cluster.local."
			for i := 0; i < 2; i++ {
				path = strings.Join(dns.SplitDomainName(path)[1:], ".")
				newstate := state.NewWithQuestion(strings.Join([]string{name, path}, "."), state.QType())
				records, extra, _, err = k.routeRequest(zone, newstate)
				if !k.IsNameError(err) && len(records) > 0 {
					records = append(records, nil)
					copy(records[1:], records)
					records[0] = newCNAME(origQName, records[0].Header().Name, records[0].Header().Ttl)
					break
				}
			}
			if !k.IsNameError(err) {
				break
			}
			// Try host search path (if set) in the next middleware
			apw := NewAutoPathWriter(w, r)
			for _, hostsearch := range k.AutoPath.HostSearchPath {
				newstate := state.NewWithQuestion(strings.Join([]string{name, hostsearch}, "."), state.QType())
				rcode, nextErr := middleware.NextOrFailure(k.Name(), k.Next, ctx, apw, newstate.Req)
				if apw.Sent {
					return rcode, nextErr
				}
			}
			// Search . in this middleware
			newstate := state.NewWithQuestion(strings.Join([]string{name, "."}, ""), state.QType())
			records, extra, _, err = k.routeRequest(zone, newstate)
			if !k.IsNameError(err) && len(records) > 0 {
				records = append(records, nil)
				copy(records[1:], records)
				records[0] = newCNAME(origQName, records[0].Header().Name, records[0].Header().Ttl)
				break
			}
			// Search . in the next middleware
			apw.Rcode = k.AutoPath.OnNXDOMAIN
			newstate = state.NewWithQuestion(strings.Join([]string{name, "."}, ""), state.QType())
			r = newstate.Req
			rcode, nextErr := middleware.NextOrFailure(k.Name(), k.Next, ctx, apw, r)
			if !apw.Sent && nextErr == nil {
				r = dnsutil.Dedup(r)
				state.SizeAndDo(r)
				r, _ = state.Scrub(r)
				apw.ForceWriteMsg(r)
			}
			return rcode, nextErr
		}
	}

	if k.IsNameError(err) {
		if k.Fallthrough {
			return middleware.NextOrFailure(k.Name(), k.Next, ctx, w, r)
		}
		// Make err nil when returning here, so we don't log spam for NXDOMAIN.
		return middleware.BackendError(&k, zone, dns.RcodeNameError, state, nil /*debug*/, nil /* err */, middleware.Options{})
	}
	if err != nil {
		return dns.RcodeServerFailure, err
	}

	if len(records) == 0 {
		return middleware.BackendError(&k, zone, dns.RcodeSuccess, state, nil /*debug*/, nil, middleware.Options{})
	}

	m.Answer = append(m.Answer, records...)
	m.Extra = append(m.Extra, extra...)

	m = dnsutil.Dedup(m)
	state.SizeAndDo(m)
	m, _ = state.Scrub(m)
	w.WriteMsg(m)
	return dns.RcodeSuccess, nil
}

func newCNAME(name string, target string, ttl uint32) *dns.CNAME {
	// TODO factor this out and put in dnsutil
	return &dns.CNAME{Hdr: dns.RR_Header{Name: name, Rrtype: dns.TypeCNAME, Class: dns.ClassINET, Ttl: ttl}, Target: dns.Fqdn(target)}
}

func (k *Kubernetes) routeRequest(zone string, state request.Request) (records []dns.RR, extra []dns.RR, debug []dns.RR, err error) {
	switch state.Type() {
	case "A":
		records, _, err = middleware.A(k, zone, state, nil, middleware.Options{})
	case "AAAA":
		records, _, err = middleware.AAAA(k, zone, state, nil, middleware.Options{})
	case "TXT":
		records, _, err = middleware.TXT(k, zone, state, middleware.Options{})
	case "CNAME":
		records, _, err = middleware.CNAME(k, zone, state, middleware.Options{})
	case "PTR":
		records, _, err = middleware.PTR(k, zone, state, middleware.Options{})
	case "MX":
		records, extra, _, err = middleware.MX(k, zone, state, middleware.Options{})
	case "SRV":
		records, extra, _, err = middleware.SRV(k, zone, state, middleware.Options{})
	case "SOA":
		records, _, err = middleware.SOA(k, zone, state, middleware.Options{})
	case "NS":
		if state.Name() == zone {
			records, extra, _, err = middleware.NS(k, zone, state, middleware.Options{})
			break
		}
		fallthrough
	default:
		// Do a fake A lookup, so we can distinguish between NODATA and NXDOMAIN
		_, _, err = middleware.A(k, zone, state, nil, middleware.Options{})
	}
	return records, extra, nil, err
}

// Name implements the Handler interface.
func (k Kubernetes) Name() string { return "kubernetes" }