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dns.go
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dns.go
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package agent
import (
"encoding/hex"
"fmt"
"log"
"net"
"strings"
"sync/atomic"
"time"
"regexp"
metrics "github.com/armon/go-metrics"
radix "github.com/armon/go-radix"
"github.com/coredns/coredns/plugin/pkg/dnsutil"
cachetype "github.com/hashicorp/consul/agent/cache-types"
"github.com/hashicorp/consul/agent/config"
"github.com/hashicorp/consul/agent/consul"
"github.com/hashicorp/consul/agent/structs"
"github.com/hashicorp/consul/api"
"github.com/hashicorp/consul/ipaddr"
"github.com/hashicorp/consul/lib"
"github.com/miekg/dns"
)
const (
// UDP can fit ~25 A records in a 512B response, and ~14 AAAA
// records. Limit further to prevent unintentional configuration
// abuse that would have a negative effect on application response
// times.
maxUDPAnswerLimit = 8
maxRecurseRecords = 5
maxRecursionLevelDefault = 3
// Increment a counter when requests staler than this are served
staleCounterThreshold = 5 * time.Second
defaultMaxUDPSize = 512
MaxDNSLabelLength = 63
)
var InvalidDnsRe = regexp.MustCompile(`[^A-Za-z0-9\\-]+`)
type dnsSOAConfig struct {
Refresh uint32 // 3600 by default
Retry uint32 // 600
Expire uint32 // 86400
Minttl uint32 // 0
}
type dnsConfig struct {
AllowStale bool
Datacenter string
EnableTruncate bool
MaxStale time.Duration
UseCache bool
CacheMaxAge time.Duration
NodeName string
NodeTTL time.Duration
OnlyPassing bool
RecursorTimeout time.Duration
Recursors []string
SegmentName string
UDPAnswerLimit int
ARecordLimit int
NodeMetaTXT bool
SOAConfig dnsSOAConfig
// TTLRadix sets service TTLs by prefix, eg: "database-*"
TTLRadix *radix.Tree
// TTLStict sets TTLs to service by full name match. It Has higher priority than TTLRadix
TTLStrict map[string]time.Duration
DisableCompression bool
}
// DNSServer is used to wrap an Agent and expose various
// service discovery endpoints using a DNS interface.
type DNSServer struct {
*dns.Server
agent *Agent
mux *dns.ServeMux
domain string
altDomain string
logger *log.Logger
// config stores the config as an atomic value (for hot-reloading). It is always of type *dnsConfig
config atomic.Value
// recursorEnabled stores whever the recursor handler is enabled as an atomic flag.
// the recursor handler is only enabled if recursors are configured. This flag is used during config hot-reloading
recursorEnabled uint32
}
func NewDNSServer(a *Agent) (*DNSServer, error) {
// Make sure domains are FQDN, make them case insensitive for ServeMux
domain := dns.Fqdn(strings.ToLower(a.config.DNSDomain))
altDomain := dns.Fqdn(strings.ToLower(a.config.DNSAltDomain))
srv := &DNSServer{
agent: a,
domain: domain,
altDomain: altDomain,
logger: a.logger,
}
cfg, err := GetDNSConfig(a.config)
if err != nil {
return nil, err
}
srv.config.Store(cfg)
return srv, nil
}
// GetDNSConfig takes global config and creates the config used by DNS server
func GetDNSConfig(conf *config.RuntimeConfig) (*dnsConfig, error) {
cfg := &dnsConfig{
AllowStale: conf.DNSAllowStale,
ARecordLimit: conf.DNSARecordLimit,
Datacenter: conf.Datacenter,
EnableTruncate: conf.DNSEnableTruncate,
MaxStale: conf.DNSMaxStale,
NodeName: conf.NodeName,
NodeTTL: conf.DNSNodeTTL,
OnlyPassing: conf.DNSOnlyPassing,
RecursorTimeout: conf.DNSRecursorTimeout,
SegmentName: conf.SegmentName,
UDPAnswerLimit: conf.DNSUDPAnswerLimit,
NodeMetaTXT: conf.DNSNodeMetaTXT,
DisableCompression: conf.DNSDisableCompression,
UseCache: conf.DNSUseCache,
CacheMaxAge: conf.DNSCacheMaxAge,
SOAConfig: dnsSOAConfig{
Expire: conf.DNSSOA.Expire,
Minttl: conf.DNSSOA.Minttl,
Refresh: conf.DNSSOA.Refresh,
Retry: conf.DNSSOA.Retry,
},
}
if conf.DNSServiceTTL != nil {
cfg.TTLRadix = radix.New()
cfg.TTLStrict = make(map[string]time.Duration)
for key, ttl := range conf.DNSServiceTTL {
// All suffix with '*' are put in radix
// This include '*' that will match anything
if strings.HasSuffix(key, "*") {
cfg.TTLRadix.Insert(key[:len(key)-1], ttl)
} else {
cfg.TTLStrict[key] = ttl
}
}
}
for _, r := range conf.DNSRecursors {
ra, err := recursorAddr(r)
if err != nil {
return nil, fmt.Errorf("Invalid recursor address: %v", err)
}
cfg.Recursors = append(cfg.Recursors, ra)
}
return cfg, nil
}
// GetTTLForService Find the TTL for a given service.
// return ttl, true if found, 0, false otherwise
func (cfg *dnsConfig) GetTTLForService(service string) (time.Duration, bool) {
if cfg.TTLStrict != nil {
ttl, ok := cfg.TTLStrict[service]
if ok {
return ttl, true
}
}
if cfg.TTLRadix != nil {
_, ttlRaw, ok := cfg.TTLRadix.LongestPrefix(service)
if ok {
return ttlRaw.(time.Duration), true
}
}
return 0, false
}
func (d *DNSServer) ListenAndServe(network, addr string, notif func()) error {
cfg := d.config.Load().(*dnsConfig)
d.mux = dns.NewServeMux()
d.mux.HandleFunc("arpa.", d.handlePtr)
d.mux.HandleFunc(d.domain, d.handleQuery)
if d.altDomain != "" {
d.mux.HandleFunc(d.altDomain, d.handleQuery)
}
d.toggleRecursorHandlerFromConfig(cfg)
d.Server = &dns.Server{
Addr: addr,
Net: network,
Handler: d.mux,
NotifyStartedFunc: notif,
}
if network == "udp" {
d.UDPSize = 65535
}
return d.Server.ListenAndServe()
}
// toggleRecursorHandlerFromConfig enables or disables the recursor handler based on config idempotently
func (d *DNSServer) toggleRecursorHandlerFromConfig(cfg *dnsConfig) {
shouldEnable := len(cfg.Recursors) > 0
if shouldEnable && atomic.CompareAndSwapUint32(&d.recursorEnabled, 0, 1) {
d.mux.HandleFunc(".", d.handleRecurse)
d.logger.Println("[DEBUG] dns: recursor enabled")
return
}
if !shouldEnable && atomic.CompareAndSwapUint32(&d.recursorEnabled, 1, 0) {
d.mux.HandleRemove(".")
d.logger.Println("[DEBUG] dns: recursor disabled")
return
}
}
// ReloadConfig hot-reloads the server config with new parameters under config.RuntimeConfig.DNS*
func (d *DNSServer) ReloadConfig(newCfg *config.RuntimeConfig) error {
cfg, err := GetDNSConfig(newCfg)
if err != nil {
return err
}
d.config.Store(cfg)
d.toggleRecursorHandlerFromConfig(cfg)
return nil
}
// setEDNS is used to set the responses EDNS size headers and
// possibly the ECS headers as well if they were present in the
// original request
func setEDNS(request *dns.Msg, response *dns.Msg, ecsGlobal bool) {
// Enable EDNS if enabled
if edns := request.IsEdns0(); edns != nil {
// cannot just use the SetEdns0 function as we need to embed
// the ECS option as well
ednsResp := new(dns.OPT)
ednsResp.Hdr.Name = "."
ednsResp.Hdr.Rrtype = dns.TypeOPT
ednsResp.SetUDPSize(edns.UDPSize())
// Setup the ECS option if present
if subnet := ednsSubnetForRequest(request); subnet != nil {
subOp := new(dns.EDNS0_SUBNET)
subOp.Code = dns.EDNS0SUBNET
subOp.Family = subnet.Family
subOp.Address = subnet.Address
subOp.SourceNetmask = subnet.SourceNetmask
if c := response.Rcode; ecsGlobal || c == dns.RcodeNameError || c == dns.RcodeServerFailure || c == dns.RcodeRefused || c == dns.RcodeNotImplemented {
// reply is globally valid and should be cached accordingly
subOp.SourceScope = 0
} else {
// reply is only valid for the subnet it was queried with
subOp.SourceScope = subnet.SourceNetmask
}
ednsResp.Option = append(ednsResp.Option, subOp)
}
response.Extra = append(response.Extra, ednsResp)
}
}
// recursorAddr is used to add a port to the recursor if omitted.
func recursorAddr(recursor string) (string, error) {
// Add the port if none
START:
_, _, err := net.SplitHostPort(recursor)
if ae, ok := err.(*net.AddrError); ok && ae.Err == "missing port in address" {
recursor = ipaddr.FormatAddressPort(recursor, 53)
goto START
}
if err != nil {
return "", err
}
// Get the address
addr, err := net.ResolveTCPAddr("tcp", recursor)
if err != nil {
return "", err
}
// Return string
return addr.String(), nil
}
// handlePtr is used to handle "reverse" DNS queries
func (d *DNSServer) handlePtr(resp dns.ResponseWriter, req *dns.Msg) {
q := req.Question[0]
defer func(s time.Time) {
metrics.MeasureSinceWithLabels([]string{"dns", "ptr_query"}, s,
[]metrics.Label{{Name: "node", Value: d.agent.config.NodeName}})
d.logger.Printf("[DEBUG] dns: request for %v (%v) from client %s (%s)",
q, time.Since(s), resp.RemoteAddr().String(),
resp.RemoteAddr().Network())
}(time.Now())
cfg := d.config.Load().(*dnsConfig)
// Setup the message response
m := new(dns.Msg)
m.SetReply(req)
m.Compress = !cfg.DisableCompression
m.Authoritative = true
m.RecursionAvailable = (len(cfg.Recursors) > 0)
// Only add the SOA if requested
if req.Question[0].Qtype == dns.TypeSOA {
d.addSOA(cfg, m)
}
datacenter := d.agent.config.Datacenter
// Get the QName without the domain suffix
qName := strings.ToLower(dns.Fqdn(req.Question[0].Name))
args := structs.DCSpecificRequest{
Datacenter: datacenter,
QueryOptions: structs.QueryOptions{
Token: d.agent.tokens.UserToken(),
AllowStale: cfg.AllowStale,
},
}
var out structs.IndexedNodes
// TODO: Replace ListNodes with an internal RPC that can do the filter
// server side to avoid transferring the entire node list.
if err := d.agent.RPC("Catalog.ListNodes", &args, &out); err == nil {
for _, n := range out.Nodes {
arpa, _ := dns.ReverseAddr(n.Address)
if arpa == qName {
ptr := &dns.PTR{
Hdr: dns.RR_Header{Name: q.Name, Rrtype: dns.TypePTR, Class: dns.ClassINET, Ttl: 0},
Ptr: fmt.Sprintf("%s.node.%s.%s", n.Node, datacenter, d.domain),
}
m.Answer = append(m.Answer, ptr)
break
}
}
}
// only look into the services if we didn't find a node
if len(m.Answer) == 0 {
// lookup the service address
serviceAddress := dnsutil.ExtractAddressFromReverse(qName)
sargs := structs.ServiceSpecificRequest{
Datacenter: datacenter,
QueryOptions: structs.QueryOptions{
Token: d.agent.tokens.UserToken(),
AllowStale: cfg.AllowStale,
},
ServiceAddress: serviceAddress,
}
var sout structs.IndexedServiceNodes
if err := d.agent.RPC("Catalog.ServiceNodes", &sargs, &sout); err == nil {
for _, n := range sout.ServiceNodes {
if n.ServiceAddress == serviceAddress {
ptr := &dns.PTR{
Hdr: dns.RR_Header{Name: q.Name, Rrtype: dns.TypePTR, Class: dns.ClassINET, Ttl: 0},
Ptr: fmt.Sprintf("%s.service.%s", n.ServiceName, d.domain),
}
m.Answer = append(m.Answer, ptr)
break
}
}
}
}
// nothing found locally, recurse
if len(m.Answer) == 0 {
d.handleRecurse(resp, req)
return
}
// ptr record responses are globally valid
setEDNS(req, m, true)
// Write out the complete response
if err := resp.WriteMsg(m); err != nil {
d.logger.Printf("[WARN] dns: failed to respond: %v", err)
}
}
// handleQuery is used to handle DNS queries in the configured domain
func (d *DNSServer) handleQuery(resp dns.ResponseWriter, req *dns.Msg) {
q := req.Question[0]
defer func(s time.Time) {
metrics.MeasureSinceWithLabels([]string{"dns", "domain_query"}, s,
[]metrics.Label{{Name: "node", Value: d.agent.config.NodeName}})
d.logger.Printf("[DEBUG] dns: request for name %v type %v class %v (took %v) from client %s (%s)",
q.Name, dns.Type(q.Qtype), dns.Class(q.Qclass), time.Since(s), resp.RemoteAddr().String(),
resp.RemoteAddr().Network())
}(time.Now())
// Switch to TCP if the client is
network := "udp"
if _, ok := resp.RemoteAddr().(*net.TCPAddr); ok {
network = "tcp"
}
cfg := d.config.Load().(*dnsConfig)
// Setup the message response
m := new(dns.Msg)
m.SetReply(req)
m.Compress = !cfg.DisableCompression
m.Authoritative = true
m.RecursionAvailable = (len(cfg.Recursors) > 0)
ecsGlobal := true
switch req.Question[0].Qtype {
case dns.TypeSOA:
ns, glue := d.nameservers(cfg, req.IsEdns0() != nil, maxRecursionLevelDefault)
m.Answer = append(m.Answer, d.soa(cfg))
m.Ns = append(m.Ns, ns...)
m.Extra = append(m.Extra, glue...)
m.SetRcode(req, dns.RcodeSuccess)
case dns.TypeNS:
ns, glue := d.nameservers(cfg, req.IsEdns0() != nil, maxRecursionLevelDefault)
m.Answer = ns
m.Extra = glue
m.SetRcode(req, dns.RcodeSuccess)
case dns.TypeAXFR:
m.SetRcode(req, dns.RcodeNotImplemented)
default:
ecsGlobal = d.dispatch(network, resp.RemoteAddr(), req, m)
}
setEDNS(req, m, ecsGlobal)
// Write out the complete response
if err := resp.WriteMsg(m); err != nil {
d.logger.Printf("[WARN] dns: failed to respond: %v", err)
}
}
func (d *DNSServer) soa(cfg *dnsConfig) *dns.SOA {
return &dns.SOA{
Hdr: dns.RR_Header{
Name: d.domain,
Rrtype: dns.TypeSOA,
Class: dns.ClassINET,
// Has to be consistent with MinTTL to avoid invalidation
Ttl: cfg.SOAConfig.Minttl,
},
Ns: "ns." + d.domain,
Serial: uint32(time.Now().Unix()),
Mbox: "hostmaster." + d.domain,
Refresh: cfg.SOAConfig.Refresh,
Retry: cfg.SOAConfig.Retry,
Expire: cfg.SOAConfig.Expire,
Minttl: cfg.SOAConfig.Minttl,
}
}
// addSOA is used to add an SOA record to a message for the given domain
func (d *DNSServer) addSOA(cfg *dnsConfig, msg *dns.Msg) {
msg.Ns = append(msg.Ns, d.soa(cfg))
}
// nameservers returns the names and ip addresses of up to three random servers
// in the current cluster which serve as authoritative name servers for zone.
func (d *DNSServer) nameservers(cfg *dnsConfig, edns bool, maxRecursionLevel int) (ns []dns.RR, extra []dns.RR) {
out, err := d.lookupServiceNodes(cfg, d.agent.config.Datacenter, structs.ConsulServiceName, "", false, maxRecursionLevel)
if err != nil {
d.logger.Printf("[WARN] dns: Unable to get list of servers: %s", err)
return nil, nil
}
if len(out.Nodes) == 0 {
d.logger.Printf("[WARN] dns: no servers found")
return
}
// shuffle the nodes to randomize the output
out.Nodes.Shuffle()
for _, o := range out.Nodes {
name, addr, dc := o.Node.Node, o.Node.Address, o.Node.Datacenter
if InvalidDnsRe.MatchString(name) {
d.logger.Printf("[WARN] dns: Skipping invalid node %q for NS records", name)
continue
}
fqdn := name + ".node." + dc + "." + d.domain
fqdn = dns.Fqdn(strings.ToLower(fqdn))
// NS record
nsrr := &dns.NS{
Hdr: dns.RR_Header{
Name: d.domain,
Rrtype: dns.TypeNS,
Class: dns.ClassINET,
Ttl: uint32(cfg.NodeTTL / time.Second),
},
Ns: fqdn,
}
ns = append(ns, nsrr)
glue, meta := d.formatNodeRecord(cfg, nil, addr, fqdn, dns.TypeANY, cfg.NodeTTL, edns, maxRecursionLevel, cfg.NodeMetaTXT)
extra = append(extra, glue...)
if meta != nil && cfg.NodeMetaTXT {
extra = append(extra, meta...)
}
// don't provide more than 3 servers
if len(ns) >= 3 {
return
}
}
return
}
// dispatch is used to parse a request and invoke the correct handler
func (d *DNSServer) dispatch(network string, remoteAddr net.Addr, req, resp *dns.Msg) (ecsGlobal bool) {
return d.doDispatch(network, remoteAddr, req, resp, maxRecursionLevelDefault)
}
// doDispatch is used to parse a request and invoke the correct handler.
// parameter maxRecursionLevel will handle whether recursive call can be performed
func (d *DNSServer) doDispatch(network string, remoteAddr net.Addr, req, resp *dns.Msg, maxRecursionLevel int) (ecsGlobal bool) {
ecsGlobal = true
// By default the query is in the default datacenter
datacenter := d.agent.config.Datacenter
// Get the QName without the domain suffix
qName := strings.ToLower(dns.Fqdn(req.Question[0].Name))
qName = d.trimDomain(qName)
// Split into the label parts
labels := dns.SplitDomainName(qName)
// Provide a flag for remembering whether the datacenter name was parsed already.
var dcParsed bool
cfg := d.config.Load().(*dnsConfig)
// The last label is either "node", "service", "query", "_<protocol>", or a datacenter name
PARSE:
n := len(labels)
if n == 0 {
goto INVALID
}
// If this is a SRV query the "service" label is optional, we add it back to use the
// existing code-path.
if req.Question[0].Qtype == dns.TypeSRV && strings.HasPrefix(labels[n-1], "_") {
labels = append(labels, "service")
n = n + 1
}
switch kind := labels[n-1]; kind {
case "service":
if n == 1 {
goto INVALID
}
// Support RFC 2782 style syntax
if n == 3 && strings.HasPrefix(labels[n-2], "_") && strings.HasPrefix(labels[n-3], "_") {
// Grab the tag since we make nuke it if it's tcp
tag := labels[n-2][1:]
// Treat _name._tcp.service.consul as a default, no need to filter on that tag
if tag == "tcp" {
tag = ""
}
// _name._tag.service.consul
d.serviceLookup(cfg, network, datacenter, labels[n-3][1:], tag, false, req, resp, maxRecursionLevel)
// Consul 0.3 and prior format for SRV queries
} else {
// Support "." in the label, re-join all the parts
tag := ""
if n >= 3 {
tag = strings.Join(labels[:n-2], ".")
}
// tag[.tag].name.service.consul
d.serviceLookup(cfg, network, datacenter, labels[n-2], tag, false, req, resp, maxRecursionLevel)
}
case "connect":
if n == 1 {
goto INVALID
}
// name.connect.consul
d.serviceLookup(cfg, network, datacenter, labels[n-2], "", true, req, resp, maxRecursionLevel)
case "node":
if n == 1 {
goto INVALID
}
// Allow a "." in the node name, just join all the parts
node := strings.Join(labels[:n-1], ".")
d.nodeLookup(cfg, network, datacenter, node, req, resp, maxRecursionLevel)
case "query":
if n == 1 {
goto INVALID
}
// Allow a "." in the query name, just join all the parts.
query := strings.Join(labels[:n-1], ".")
ecsGlobal = false
d.preparedQueryLookup(cfg, network, datacenter, query, remoteAddr, req, resp, maxRecursionLevel)
case "addr":
if n != 2 {
goto INVALID
}
switch len(labels[0]) / 2 {
// IPv4
case 4:
ip, err := hex.DecodeString(labels[0])
if err != nil {
goto INVALID
}
resp.Answer = append(resp.Answer, &dns.A{
Hdr: dns.RR_Header{
Name: qName + d.domain,
Rrtype: dns.TypeA,
Class: dns.ClassINET,
Ttl: uint32(cfg.NodeTTL / time.Second),
},
A: ip,
})
// IPv6
case 16:
ip, err := hex.DecodeString(labels[0])
if err != nil {
goto INVALID
}
resp.Answer = append(resp.Answer, &dns.AAAA{
Hdr: dns.RR_Header{
Name: qName + d.domain,
Rrtype: dns.TypeAAAA,
Class: dns.ClassINET,
Ttl: uint32(cfg.NodeTTL / time.Second),
},
AAAA: ip,
})
}
default:
// https://github.com/hashicorp/consul/issues/3200
//
// Since datacenter names cannot contain dots we can only allow one
// label between the query type and the domain to be the datacenter name.
// Since the datacenter name is optional and the parser strips off labels at the end until it finds a suitable
// query type label we return NXDOMAIN when we encounter another label
// which could be the datacenter name.
//
// If '.consul' is the domain then
// * foo.service.dc.consul is OK
// * foo.service.dc.stuff.consul is not OK
if dcParsed {
goto INVALID
}
dcParsed = true
// Store the DC, and re-parse
datacenter = labels[n-1]
labels = labels[:n-1]
goto PARSE
}
return
INVALID:
d.logger.Printf("[WARN] dns: QName invalid: %s", qName)
d.addSOA(cfg, resp)
resp.SetRcode(req, dns.RcodeNameError)
return
}
func (d *DNSServer) trimDomain(query string) string {
longer := d.domain
shorter := d.altDomain
if len(shorter) > len(longer) {
longer, shorter = shorter, longer
}
if strings.HasSuffix(query, longer) {
return strings.TrimSuffix(query, longer)
}
return strings.TrimSuffix(query, shorter)
}
// nodeLookup is used to handle a node query
func (d *DNSServer) nodeLookup(cfg *dnsConfig, network, datacenter, node string, req, resp *dns.Msg, maxRecursionLevel int) {
// Only handle ANY, A, AAAA, and TXT type requests
qType := req.Question[0].Qtype
if qType != dns.TypeANY && qType != dns.TypeA && qType != dns.TypeAAAA && qType != dns.TypeTXT {
return
}
// Make an RPC request
args := &structs.NodeSpecificRequest{
Datacenter: datacenter,
Node: node,
QueryOptions: structs.QueryOptions{
Token: d.agent.tokens.UserToken(),
AllowStale: cfg.AllowStale,
},
}
out, err := d.lookupNode(cfg, args)
if err != nil {
d.logger.Printf("[ERR] dns: rpc error: %v", err)
resp.SetRcode(req, dns.RcodeServerFailure)
return
}
// If we have no address, return not found!
if out.NodeServices == nil {
d.addSOA(cfg, resp)
resp.SetRcode(req, dns.RcodeNameError)
return
}
generateMeta := false
metaInAnswer := false
if qType == dns.TypeANY || qType == dns.TypeTXT {
generateMeta = true
metaInAnswer = true
} else if cfg.NodeMetaTXT {
generateMeta = true
}
// Add the node record
n := out.NodeServices.Node
edns := req.IsEdns0() != nil
addr := d.agent.TranslateAddress(datacenter, n.Address, n.TaggedAddresses)
records, meta := d.formatNodeRecord(cfg, out.NodeServices.Node, addr, req.Question[0].Name, qType, cfg.NodeTTL, edns, maxRecursionLevel, generateMeta)
if records != nil {
resp.Answer = append(resp.Answer, records...)
}
if meta != nil && metaInAnswer && generateMeta {
resp.Answer = append(resp.Answer, meta...)
} else if meta != nil && cfg.NodeMetaTXT {
resp.Extra = append(resp.Extra, meta...)
}
}
func (d *DNSServer) lookupNode(cfg *dnsConfig, args *structs.NodeSpecificRequest) (*structs.IndexedNodeServices, error) {
var out structs.IndexedNodeServices
useCache := cfg.UseCache
RPC:
if useCache {
raw, _, err := d.agent.cache.Get(cachetype.NodeServicesName, args)
if err != nil {
return nil, err
}
reply, ok := raw.(*structs.IndexedNodeServices)
if !ok {
// This should never happen, but we want to protect against panics
return nil, fmt.Errorf("internal error: response type not correct")
}
out = *reply
} else {
if err := d.agent.RPC("Catalog.NodeServices", &args, &out); err != nil {
return nil, err
}
}
// Verify that request is not too stale, redo the request
if args.AllowStale {
if out.LastContact > cfg.MaxStale {
args.AllowStale = false
useCache = false
d.logger.Printf("[WARN] dns: Query results too stale, re-requesting")
goto RPC
} else if out.LastContact > staleCounterThreshold {
metrics.IncrCounter([]string{"dns", "stale_queries"}, 1)
}
}
return &out, nil
}
// encodeKVasRFC1464 encodes a key-value pair according to RFC1464
func encodeKVasRFC1464(key, value string) (txt string) {
// For details on these replacements c.f. https://www.ietf.org/rfc/rfc1464.txt
key = strings.Replace(key, "`", "``", -1)
key = strings.Replace(key, "=", "`=", -1)
// Backquote the leading spaces
leadingSpacesRE := regexp.MustCompile("^ +")
numLeadingSpaces := len(leadingSpacesRE.FindString(key))
key = leadingSpacesRE.ReplaceAllString(key, strings.Repeat("` ", numLeadingSpaces))
// Backquote the trailing spaces
trailingSpacesRE := regexp.MustCompile(" +$")
numTrailingSpaces := len(trailingSpacesRE.FindString(key))
key = trailingSpacesRE.ReplaceAllString(key, strings.Repeat("` ", numTrailingSpaces))
value = strings.Replace(value, "`", "``", -1)
return key + "=" + value
}
// formatNodeRecord takes a Node and returns the RRs associated with that node
//
// The return value is two slices. The first slice is the main answer slice (containing the A, AAAA, CNAME) RRs for the node
// and the second slice contains any TXT RRs created from the node metadata. It is up to the caller to determine where the
// generated RRs should go and if they should be used at all.
func (d *DNSServer) formatNodeRecord(cfg *dnsConfig, node *structs.Node, addr, qName string, qType uint16, ttl time.Duration, edns bool, maxRecursionLevel int, generateMeta bool) (records, meta []dns.RR) {
// Parse the IP
ip := net.ParseIP(addr)
var ipv4 net.IP
if ip != nil {
ipv4 = ip.To4()
}
switch {
case ipv4 != nil && (qType == dns.TypeANY || qType == dns.TypeA):
records = append(records, &dns.A{
Hdr: dns.RR_Header{
Name: qName,
Rrtype: dns.TypeA,
Class: dns.ClassINET,
Ttl: uint32(ttl / time.Second),
},
A: ip,
})
case ip != nil && ipv4 == nil && (qType == dns.TypeANY || qType == dns.TypeAAAA):
records = append(records, &dns.AAAA{
Hdr: dns.RR_Header{
Name: qName,
Rrtype: dns.TypeAAAA,
Class: dns.ClassINET,
Ttl: uint32(ttl / time.Second),
},
AAAA: ip,
})
case ip == nil && (qType == dns.TypeANY || qType == dns.TypeCNAME ||
qType == dns.TypeA || qType == dns.TypeAAAA || qType == dns.TypeTXT):
// Get the CNAME
cnRec := &dns.CNAME{
Hdr: dns.RR_Header{
Name: qName,
Rrtype: dns.TypeCNAME,
Class: dns.ClassINET,
Ttl: uint32(ttl / time.Second),
},
Target: dns.Fqdn(addr),
}
records = append(records, cnRec)
// Recurse
more := d.resolveCNAME(cfg, cnRec.Target, maxRecursionLevel)
extra := 0
MORE_REC:
for _, rr := range more {
switch rr.Header().Rrtype {
case dns.TypeCNAME, dns.TypeA, dns.TypeAAAA, dns.TypeTXT:
records = append(records, rr)
extra++
if extra == maxRecurseRecords && !edns {
break MORE_REC
}
}
}
}
if node != nil && generateMeta {
for key, value := range node.Meta {
txt := value
if !strings.HasPrefix(strings.ToLower(key), "rfc1035-") {
txt = encodeKVasRFC1464(key, value)
}
meta = append(meta, &dns.TXT{
Hdr: dns.RR_Header{
Name: qName,
Rrtype: dns.TypeTXT,
Class: dns.ClassINET,
Ttl: uint32(ttl / time.Second),
},
Txt: []string{txt},
})
}
}
return records, meta
}
// indexRRs populates a map which indexes a given list of RRs by name. NOTE that
// the names are all squashed to lower case so we can perform case-insensitive
// lookups; the RRs are not modified.
func indexRRs(rrs []dns.RR, index map[string]dns.RR) {
for _, rr := range rrs {
name := strings.ToLower(rr.Header().Name)
if _, ok := index[name]; !ok {
index[name] = rr
}
}
}
// syncExtra takes a DNS response message and sets the extra data to the most
// minimal set needed to cover the answer data. A pre-made index of RRs is given
// so that can be re-used between calls. This assumes that the extra data is
// only used to provide info for SRV records. If that's not the case, then this
// will wipe out any additional data.
func syncExtra(index map[string]dns.RR, resp *dns.Msg) {
extra := make([]dns.RR, 0, len(resp.Answer))
resolved := make(map[string]struct{}, len(resp.Answer))
for _, ansRR := range resp.Answer {
srv, ok := ansRR.(*dns.SRV)
if !ok {
continue
}
// Note that we always use lower case when using the index so
// that compares are not case-sensitive. We don't alter the actual
// RRs we add into the extra section, however.
target := strings.ToLower(srv.Target)
RESOLVE:
if _, ok := resolved[target]; ok {
continue
}
resolved[target] = struct{}{}
extraRR, ok := index[target]
if ok {
extra = append(extra, extraRR)
if cname, ok := extraRR.(*dns.CNAME); ok {
target = strings.ToLower(cname.Target)
goto RESOLVE
}
}
}
resp.Extra = extra
}
// dnsBinaryTruncate find the optimal number of records using a fast binary search and return
// it in order to return a DNS answer lower than maxSize parameter.
func dnsBinaryTruncate(resp *dns.Msg, maxSize int, index map[string]dns.RR, hasExtra bool) int {
originalAnswser := resp.Answer
startIndex := 0
endIndex := len(resp.Answer) + 1
for endIndex-startIndex > 1 {
median := startIndex + (endIndex-startIndex)/2
resp.Answer = originalAnswser[:median]
if hasExtra {
syncExtra(index, resp)
}
aLen := resp.Len()
if aLen <= maxSize {
if maxSize-aLen < 10 {
// We are good, increasing will go out of bounds
return median
}
startIndex = median
} else {
endIndex = median
}
}
return startIndex
}
// trimTCPResponse limit the MaximumSize of messages to 64k as it is the limit
// of DNS responses
func (d *DNSServer) trimTCPResponse(req, resp *dns.Msg) (trimmed bool) {
hasExtra := len(resp.Extra) > 0
// There is some overhead, 65535 does not work
maxSize := 65523 // 64k - 12 bytes DNS raw overhead
// We avoid some function calls and allocations by only handling the
// extra data when necessary.
var index map[string]dns.RR
originalSize := resp.Len()
originalNumRecords := len(resp.Answer)
// It is not possible to return more than 4k records even with compression
// Since we are performing binary search it is not a big deal, but it
// improves a bit performance, even with binary search
truncateAt := 4096