plugin/nomad: Add a Nomad plugin (#7467)

Signed-off-by: Olli Janatuinen <olli.janatuinen@gmail.com>

plugin/nomad/nomad.go

@@ -0,0 +1,158 @@
+package nomad
+
+import (
+	"context"
+	"fmt"
+	"net"
+
+	"github.com/coredns/coredns/plugin"
+	"github.com/coredns/coredns/plugin/metrics"
+	"github.com/coredns/coredns/plugin/pkg/dnsutil"
+	clog "github.com/coredns/coredns/plugin/pkg/log"
+	"github.com/coredns/coredns/request"
+
+	"github.com/hashicorp/nomad/api"
+	"github.com/miekg/dns"
+)
+
+const pluginName = "nomad"
+
+var (
+	log        = clog.NewWithPlugin(pluginName)
+	defaultTTL = 30
+)
+
+type Nomad struct {
+	Next plugin.Handler
+
+	ttl     uint32
+	Zone    string
+	clients []*api.Client
+	current int
+}
+
+func (n *Nomad) Name() string {
+	return pluginName
+}
+
+func (n Nomad) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
+	state := request.Request{W: w, Req: r}
+	qname, originalQName, err := processQName(state.Name(), n.Zone)
+	if err != nil {
+		return plugin.NextOrFailure(n.Name(), n.Next, ctx, w, r)
+	}
+
+	namespace, serviceName, err := extractNamespaceAndService(qname)
+	if err != nil {
+		return plugin.NextOrFailure(n.Name(), n.Next, ctx, w, r)
+	}
+
+	m, header := initializeMessage(state, n.ttl)
+
+	svcRegistrations, _, err := fetchServiceRegistrations(n, serviceName, namespace)
+	if err != nil {
+		log.Warning(err)
+		return handleServiceLookupError(w, m, ctx, namespace)
+	}
+
+	if len(svcRegistrations) == 0 {
+		return handleResponseError(n, w, m, originalQName, n.ttl, ctx, namespace, err)
+	}
+
+	if err := addServiceResponses(m, svcRegistrations, header, state.QType(), originalQName, n.ttl); err != nil {
+		return handleResponseError(n, w, m, originalQName, n.ttl, ctx, namespace, err)
+	}
+
+	err = w.WriteMsg(m)
+	requestSuccessCount.WithLabelValues(metrics.WithServer(ctx), namespace).Inc()
+	return dns.RcodeSuccess, err
+}
+
+func processQName(qname, zone string) (string, string, error) {
+	original := dns.Fqdn(qname)
+	base, err := dnsutil.TrimZone(original, dns.Fqdn(zone))
+	return base, original, err
+}
+
+func extractNamespaceAndService(qname string) (string, string, error) {
+	qnameSplit := dns.SplitDomainName(qname)
+	if len(qnameSplit) < 2 {
+		return "", "", fmt.Errorf("invalid query name")
+	}
+	return qnameSplit[1], qnameSplit[0], nil
+}
+
+func initializeMessage(state request.Request, ttl uint32) (*dns.Msg, dns.RR_Header) {
+	m := new(dns.Msg)
+	m.SetReply(state.Req)
+	m.Authoritative, m.Compress, m.Rcode = true, true, dns.RcodeSuccess
+
+	header := dns.RR_Header{
+		Name:   state.QName(),
+		Rrtype: state.QType(),
+		Class:  dns.ClassINET,
+		Ttl:    ttl,
+	}
+
+	return m, header
+}
+
+func fetchServiceRegistrations(n Nomad, serviceName, namespace string) ([]*api.ServiceRegistration, *api.QueryMeta, error) {
+	log.Debugf("Looking up record for svc: %s namespace: %s", serviceName, namespace)
+	nc, err := n.getClient()
+	if err != nil {
+		return nil, nil, err
+	}
+	return nc.Services().Get(serviceName, (&api.QueryOptions{Namespace: namespace}))
+}
+
+func handleServiceLookupError(w dns.ResponseWriter, m *dns.Msg, ctx context.Context, namespace string) (int, error) {
+	m.Rcode = dns.RcodeSuccess
+	err := w.WriteMsg(m)
+	requestFailedCount.WithLabelValues(metrics.WithServer(ctx), namespace).Inc()
+	return dns.RcodeServerFailure, err
+}
+
+func addServiceResponses(m *dns.Msg, svcRegistrations []*api.ServiceRegistration, header dns.RR_Header, qtype uint16, originalQName string, ttl uint32) error {
+	for _, s := range svcRegistrations {
+		addr := net.ParseIP(s.Address)
+		if addr == nil {
+			return fmt.Errorf("error parsing IP address")
+		}
+
+		switch qtype {
+		case dns.TypeA:
+			if addr.To4() == nil {
+				continue
+			}
+			addARecord(m, header, addr)
+		case dns.TypeAAAA:
+			if addr.To4() != nil {
+				continue
+			}
+			addAAAARecord(m, header, addr)
+		case dns.TypeSRV:
+			err := addSRVRecord(m, s, header, originalQName, addr, ttl)
+			if err != nil {
+				return err
+			}
+		default:
+			m.Rcode = dns.RcodeNotImplemented
+			return fmt.Errorf("query type not implemented")
+		}
+	}
+	return nil
+}
+
+func handleResponseError(n Nomad, w dns.ResponseWriter, m *dns.Msg, originalQName string, ttl uint32, ctx context.Context, namespace string, err error) (int, error) {
+	m.Rcode = dns.RcodeNameError
+	m.Answer = append(m.Answer, createSOARecord(originalQName, ttl, n.Zone))
+
+	if writeErr := w.WriteMsg(m); writeErr != nil {
+		return dns.RcodeServerFailure, fmt.Errorf("write message error: %w", writeErr)
+	}
+
+	requestFailedCount.WithLabelValues(metrics.WithServer(ctx), namespace).Inc()
+
+	return dns.RcodeSuccess, err
+}