356 lines
8.4 KiB
Go
356 lines
8.4 KiB
Go
package agent
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import (
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"fmt"
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"github.com/hashicorp/consul/consul/structs"
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"github.com/miekg/dns"
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"io"
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"log"
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"net"
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"strings"
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"time"
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)
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const (
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testQuery = "_test.consul."
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consulDomain = "consul."
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)
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// DNSServer is used to wrap an Agent and expose various
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// service discovery endpoints using a DNS interface.
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type DNSServer struct {
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agent *Agent
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dnsHandler *dns.ServeMux
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dnsServer *dns.Server
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domain string
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logger *log.Logger
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}
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// NewDNSServer starts a new DNS server to provide an agent interface
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func NewDNSServer(agent *Agent, logOutput io.Writer, domain, bind string) (*DNSServer, error) {
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// Make sure domain is FQDN
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domain = dns.Fqdn(domain)
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// Construct the DNS components
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mux := dns.NewServeMux()
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// Setup the server
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server := &dns.Server{
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Addr: bind,
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Net: "udp",
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Handler: mux,
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UDPSize: 65535,
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}
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// Create the server
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srv := &DNSServer{
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agent: agent,
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dnsHandler: mux,
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dnsServer: server,
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domain: domain,
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logger: log.New(logOutput, "", log.LstdFlags),
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}
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// Register mux handlers, always handle "consul."
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mux.HandleFunc(domain, srv.handleQuery)
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if domain != consulDomain {
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mux.HandleFunc(consulDomain, srv.handleTest)
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}
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// Async start the DNS Server, handle a potential error
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errCh := make(chan error, 1)
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go func() {
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err := server.ListenAndServe()
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srv.logger.Printf("[ERR] dns: error starting server: %v", err)
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errCh <- err
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}()
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// Check the server is running, do a test lookup
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checkCh := make(chan error, 1)
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go func() {
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// This is jank, but we have no way to edge trigger on
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// the start of our server, so we just wait and hope it is up.
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time.Sleep(50 * time.Millisecond)
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m := new(dns.Msg)
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m.SetQuestion(testQuery, dns.TypeANY)
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c := new(dns.Client)
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in, _, err := c.Exchange(m, bind)
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if err != nil {
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checkCh <- err
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return
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}
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if len(in.Answer) == 0 {
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checkCh <- fmt.Errorf("no response to test message")
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return
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}
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close(checkCh)
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}()
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// Wait for either the check, listen error, or timeout
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select {
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case e := <-errCh:
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return srv, e
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case e := <-checkCh:
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return srv, e
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case <-time.After(time.Second):
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return srv, fmt.Errorf("timeout setting up DNS server")
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}
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return srv, nil
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}
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// handleQUery is used to handle DNS queries in the configured domain
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func (d *DNSServer) handleQuery(resp dns.ResponseWriter, req *dns.Msg) {
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q := req.Question[0]
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defer func(s time.Time) {
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d.logger.Printf("[DEBUG] dns: request for %v (%v)", q, time.Now().Sub(s))
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}(time.Now())
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// Check if this is potentially a test query
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if q.Name == testQuery {
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d.handleTest(resp, req)
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return
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}
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// Setup the message response
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m := new(dns.Msg)
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m.SetReply(req)
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m.Authoritative = true
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d.addSOA(d.domain, m)
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defer resp.WriteMsg(m)
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// Dispatch the correct handler
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d.dispatch(req, m)
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}
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// handleTest is used to handle DNS queries in the ".consul." domain
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func (d *DNSServer) handleTest(resp dns.ResponseWriter, req *dns.Msg) {
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q := req.Question[0]
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defer func(s time.Time) {
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d.logger.Printf("[DEBUG] dns: request for %v (%v)", q, time.Now().Sub(s))
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}(time.Now())
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if !(q.Qtype == dns.TypeANY || q.Qtype == dns.TypeTXT) {
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return
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}
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if q.Name != testQuery {
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return
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}
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// Always respond with TXT "ok"
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m := new(dns.Msg)
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m.SetReply(req)
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m.Authoritative = true
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header := dns.RR_Header{Name: q.Name, Rrtype: dns.TypeTXT, Class: dns.ClassINET, Ttl: 0}
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txt := &dns.TXT{header, []string{"ok"}}
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m.Answer = append(m.Answer, txt)
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d.addSOA(consulDomain, m)
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resp.WriteMsg(m)
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}
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// addSOA is used to add an SOA record to a message for the given domain
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func (d *DNSServer) addSOA(domain string, msg *dns.Msg) {
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soa := &dns.SOA{
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Hdr: dns.RR_Header{
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Name: domain,
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Rrtype: dns.TypeSOA,
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Class: dns.ClassINET,
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Ttl: 0,
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},
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Ns: "ns." + domain,
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Mbox: "postmaster." + domain,
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Serial: uint32(time.Now().Unix()),
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Refresh: 3600,
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Retry: 600,
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Expire: 86400,
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Minttl: 0,
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}
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msg.Ns = append(msg.Ns, soa)
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}
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// dispatch is used to parse a request and invoke the correct handler
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func (d *DNSServer) dispatch(req, resp *dns.Msg) {
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// By default the query is in the default datacenter
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datacenter := d.agent.config.Datacenter
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// Get the QName without the domain suffix
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qName := dns.Fqdn(req.Question[0].Name)
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qName = strings.TrimSuffix(qName, d.domain)
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// Split into the label parts
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labels := dns.SplitDomainName(qName)
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// The last label is either "node", "service" or a datacenter name
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PARSE:
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if len(labels) == 0 {
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goto INVALID
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}
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switch labels[len(labels)-1] {
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case "service":
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// Handle lookup with and without tag
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switch len(labels) {
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case 2:
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d.serviceLookup(datacenter, labels[0], "", req, resp)
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case 3:
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d.serviceLookup(datacenter, labels[1], labels[0], req, resp)
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default:
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goto INVALID
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}
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case "node":
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if len(labels) != 2 {
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goto INVALID
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}
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d.nodeLookup(datacenter, labels[0], req, resp)
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default:
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// Store the DC, and re-parse
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datacenter = labels[len(labels)-1]
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labels = labels[:len(labels)-1]
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goto PARSE
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}
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return
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INVALID:
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d.logger.Printf("[WARN] dns: QName invalid: %s", qName)
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resp.SetRcode(req, dns.RcodeNameError)
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}
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// nodeLookup is used to handle a node query
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func (d *DNSServer) nodeLookup(datacenter, node string, req, resp *dns.Msg) {
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// Only handle ANY and A type requests
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qType := req.Question[0].Qtype
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if qType != dns.TypeANY && qType != dns.TypeA {
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return
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}
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// Make an RPC request
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args := structs.NodeServicesRequest{
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Datacenter: datacenter,
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Node: node,
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}
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var out structs.NodeServices
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if err := d.agent.RPC("Catalog.NodeServices", &args, &out); err != nil {
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d.logger.Printf("[ERR] dns: rpc error: %v", err)
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resp.SetRcode(req, dns.RcodeServerFailure)
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return
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}
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// If we have no address, return not found!
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if out.Address == "" {
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resp.SetRcode(req, dns.RcodeNameError)
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return
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}
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// Parse the IP
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ip := net.ParseIP(out.Address)
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if ip == nil {
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d.logger.Printf("[ERR] dns: failed to parse IP %v for %v", out.Address, node)
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resp.SetRcode(req, dns.RcodeServerFailure)
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return
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}
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// Format A record
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aRec := &dns.A{
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Hdr: dns.RR_Header{
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Name: req.Question[0].Name,
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Rrtype: dns.TypeA,
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Class: dns.ClassINET,
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Ttl: 0,
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},
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A: ip,
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}
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// Add the response
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resp.Answer = append(resp.Answer, aRec)
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}
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// serviceLookup is used to handle a service query
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func (d *DNSServer) serviceLookup(datacenter, service, tag string, req, resp *dns.Msg) {
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// Make an RPC request
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args := structs.ServiceNodesRequest{
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Datacenter: datacenter,
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ServiceName: service,
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ServiceTag: tag,
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TagFilter: tag != "",
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}
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var out structs.ServiceNodes
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if err := d.agent.RPC("Catalog.ServiceNodes", &args, &out); err != nil {
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d.logger.Printf("[ERR] dns: rpc error: %v", err)
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resp.SetRcode(req, dns.RcodeServerFailure)
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return
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}
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// If we have no nodes, return not found!
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if len(out) == 0 {
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resp.SetRcode(req, dns.RcodeNameError)
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return
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}
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// Add various responses depending on the request
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qType := req.Question[0].Qtype
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if qType == dns.TypeANY || qType == dns.TypeA {
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d.serviceARecords(out, req, resp)
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}
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if qType == dns.TypeANY || qType == dns.TypeSRV {
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d.serviceSRVRecords(datacenter, out, req, resp)
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}
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}
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// serviceARecords is used to add the A records for a service lookup
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func (d *DNSServer) serviceARecords(nodes structs.ServiceNodes, req, resp *dns.Msg) {
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for _, node := range nodes {
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ip := net.ParseIP(node.Address)
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if ip == nil {
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d.logger.Printf("[ERR] dns: failed to parse IP %v for %v", node.Address, node.Node)
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continue
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}
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aRec := &dns.A{
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Hdr: dns.RR_Header{
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Name: req.Question[0].Name,
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Rrtype: dns.TypeA,
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Class: dns.ClassINET,
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Ttl: 0,
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},
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A: ip,
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}
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resp.Answer = append(resp.Answer, aRec)
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}
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}
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// serviceARecords is used to add the SRV records for a service lookup
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func (d *DNSServer) serviceSRVRecords(dc string, nodes structs.ServiceNodes, req, resp *dns.Msg) {
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for _, node := range nodes {
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srvRec := &dns.SRV{
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Hdr: dns.RR_Header{
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Name: req.Question[0].Name,
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Rrtype: dns.TypeSRV,
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Class: dns.ClassINET,
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Ttl: 0,
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},
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Priority: 1,
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Weight: 1,
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Port: uint16(node.ServicePort),
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Target: fmt.Sprintf("%s.node.%s.%s", node.Node, dc, d.domain),
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}
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resp.Answer = append(resp.Answer, srvRec)
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ip := net.ParseIP(node.Address)
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if ip == nil {
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d.logger.Printf("[ERR] dns: failed to parse IP %v for %v", node.Address, node.Node)
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continue
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}
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aRec := &dns.A{
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Hdr: dns.RR_Header{
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Name: srvRec.Target,
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Rrtype: dns.TypeA,
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Class: dns.ClassINET,
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Ttl: 0,
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},
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A: ip,
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}
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resp.Extra = append(resp.Extra, aRec)
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}
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}
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