open-consul/agent/dns.go

1259 lines
36 KiB
Go

package agent
import (
"encoding/hex"
"fmt"
"log"
"net"
"strings"
"sync/atomic"
"time"
"regexp"
"github.com/armon/go-metrics"
"github.com/hashicorp/consul/agent/config"
"github.com/hashicorp/consul/agent/consul"
"github.com/hashicorp/consul/agent/structs"
"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
// 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 dnsConfig struct {
AllowStale bool
Datacenter string
EnableTruncate bool
MaxStale time.Duration
NodeName string
NodeTTL time.Duration
OnlyPassing bool
RecursorTimeout time.Duration
SegmentName string
ServiceTTL map[string]time.Duration
UDPAnswerLimit int
ARecordLimit int
}
// DNSServer is used to wrap an Agent and expose various
// service discovery endpoints using a DNS interface.
type DNSServer struct {
*dns.Server
agent *Agent
config *dnsConfig
domain string
recursors []string
logger *log.Logger
// disableCompression is the config.DisableCompression flag that can
// be safely changed at runtime. It always contains a bool and is
// initialized with the value from config.DisableCompression.
disableCompression atomic.Value
}
func NewDNSServer(a *Agent) (*DNSServer, error) {
var recursors []string
for _, r := range a.config.DNSRecursors {
ra, err := recursorAddr(r)
if err != nil {
return nil, fmt.Errorf("Invalid recursor address: %v", err)
}
recursors = append(recursors, ra)
}
// Make sure domain is FQDN, make it case insensitive for ServeMux
domain := dns.Fqdn(strings.ToLower(a.config.DNSDomain))
dnscfg := GetDNSConfig(a.config)
srv := &DNSServer{
agent: a,
config: dnscfg,
domain: domain,
logger: a.logger,
recursors: recursors,
}
srv.disableCompression.Store(a.config.DNSDisableCompression)
return srv, nil
}
func GetDNSConfig(conf *config.RuntimeConfig) *dnsConfig {
return &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,
ServiceTTL: conf.DNSServiceTTL,
UDPAnswerLimit: conf.DNSUDPAnswerLimit,
}
}
func (d *DNSServer) ListenAndServe(network, addr string, notif func()) error {
mux := dns.NewServeMux()
mux.HandleFunc("arpa.", d.handlePtr)
mux.HandleFunc(d.domain, d.handleQuery)
if len(d.recursors) > 0 {
mux.HandleFunc(".", d.handleRecurse)
}
d.Server = &dns.Server{
Addr: addr,
Net: network,
Handler: mux,
NotifyStartedFunc: notif,
}
if network == "udp" {
d.UDPSize = 65535
}
return d.Server.ListenAndServe()
}
// 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 = fmt.Sprintf("%s:%d", 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{"consul", "dns", "ptr_query"}, s,
[]metrics.Label{{Name: "node", Value: d.agent.config.NodeName}})
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())
// Setup the message response
m := new(dns.Msg)
m.SetReply(req)
m.Compress = !d.disableCompression.Load().(bool)
m.Authoritative = true
m.RecursionAvailable = (len(d.recursors) > 0)
// Only add the SOA if requested
if req.Question[0].Qtype == dns.TypeSOA {
d.addSOA(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: d.config.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
}
}
}
// nothing found locally, recurse
if len(m.Answer) == 0 {
d.handleRecurse(resp, req)
return
}
// Enable EDNS if enabled
if edns := req.IsEdns0(); edns != nil {
m.SetEdns0(edns.UDPSize(), false)
}
// 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{"consul", "dns", "domain_query"}, s,
[]metrics.Label{{Name: "node", Value: d.agent.config.NodeName}})
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"
}
// Setup the message response
m := new(dns.Msg)
m.SetReply(req)
m.Compress = !d.disableCompression.Load().(bool)
m.Authoritative = true
m.RecursionAvailable = (len(d.recursors) > 0)
switch req.Question[0].Qtype {
case dns.TypeSOA:
ns, glue := d.nameservers(req.IsEdns0() != nil)
m.Answer = append(m.Answer, d.soa())
m.Ns = append(m.Ns, ns...)
m.Extra = append(m.Extra, glue...)
m.SetRcode(req, dns.RcodeSuccess)
case dns.TypeNS:
ns, glue := d.nameservers(req.IsEdns0() != nil)
m.Answer = ns
m.Extra = glue
m.SetRcode(req, dns.RcodeSuccess)
case dns.TypeAXFR:
m.SetRcode(req, dns.RcodeNotImplemented)
default:
d.dispatch(network, resp.RemoteAddr(), req, m)
}
// Handle EDNS
if edns := req.IsEdns0(); edns != nil {
m.SetEdns0(edns.UDPSize(), false)
}
// 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() *dns.SOA {
return &dns.SOA{
Hdr: dns.RR_Header{
Name: d.domain,
Rrtype: dns.TypeSOA,
Class: dns.ClassINET,
Ttl: 0,
},
Ns: "ns." + d.domain,
Serial: uint32(time.Now().Unix()),
// todo(fs): make these configurable
Mbox: "hostmaster." + d.domain,
Refresh: 3600,
Retry: 600,
Expire: 86400,
Minttl: 0,
}
}
// addSOA is used to add an SOA record to a message for the given domain
func (d *DNSServer) addSOA(msg *dns.Msg) {
msg.Ns = append(msg.Ns, d.soa())
}
// 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(edns bool) (ns []dns.RR, extra []dns.RR) {
out, err := d.lookupServiceNodes(d.agent.config.Datacenter, structs.ConsulServiceName, "")
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(d.config.NodeTTL / time.Second),
},
Ns: fqdn,
}
ns = append(ns, nsrr)
glue := d.formatNodeRecord(nil, addr, fqdn, dns.TypeANY, d.config.NodeTTL, edns)
extra = append(extra, glue...)
// 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) {
// 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 = strings.TrimSuffix(qName, d.domain)
// Split into the label parts
labels := dns.SplitDomainName(qName)
// Provide a flag for remembering whether the datacenter name was parsed already.
var dcParsed bool
// 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 labels[n-1] {
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(network, datacenter, labels[n-3][1:], tag, req, resp)
// 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(network, datacenter, labels[n-2], tag, req, resp)
}
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(network, datacenter, node, req, resp)
case "query":
if n == 1 {
goto INVALID
}
// Allow a "." in the query name, just join all the parts.
query := strings.Join(labels[:n-1], ".")
d.preparedQueryLookup(network, datacenter, query, remoteAddr, req, resp)
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(d.config.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(d.config.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(resp)
resp.SetRcode(req, dns.RcodeNameError)
}
// nodeLookup is used to handle a node query
func (d *DNSServer) nodeLookup(network, datacenter, node string, req, resp *dns.Msg) {
// 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: d.config.AllowStale,
},
}
var out structs.IndexedNodeServices
RPC:
if err := d.agent.RPC("Catalog.NodeServices", &args, &out); err != nil {
d.logger.Printf("[ERR] dns: rpc error: %v", err)
resp.SetRcode(req, dns.RcodeServerFailure)
return
}
// Verify that request is not too stale, redo the request
if args.AllowStale {
if out.LastContact > d.config.MaxStale {
args.AllowStale = false
d.logger.Printf("[WARN] dns: Query results too stale, re-requesting")
goto RPC
} else if out.LastContact > staleCounterThreshold {
metrics.IncrCounter([]string{"consul", "dns", "stale_queries"}, 1)
metrics.IncrCounter([]string{"dns", "stale_queries"}, 1)
}
}
// If we have no address, return not found!
if out.NodeServices == nil {
d.addSOA(resp)
resp.SetRcode(req, dns.RcodeNameError)
return
}
// Add the node record
n := out.NodeServices.Node
edns := req.IsEdns0() != nil
addr := d.agent.TranslateAddress(datacenter, n.Address, n.TaggedAddresses)
records := d.formatNodeRecord(out.NodeServices.Node, addr, req.Question[0].Name, qType, d.config.NodeTTL, edns)
if records != nil {
resp.Answer = append(resp.Answer, records...)
}
}
// 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 an A, AAAA, TXT or CNAME record
func (d *DNSServer) formatNodeRecord(node *structs.Node, addr, qName string, qType uint16, ttl time.Duration, edns bool) (records []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(cnRec.Target)
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 && (qType == dns.TypeANY || qType == dns.TypeTXT) {
for key, value := range node.Meta {
txt := value
if !strings.HasPrefix(strings.ToLower(key), "rfc1035-") {
txt = encodeKVasRFC1464(key, value)
}
records = append(records, &dns.TXT{
Hdr: dns.RR_Header{
Name: qName,
Rrtype: dns.TypeTXT,
Class: dns.ClassINET,
Ttl: uint32(ttl / time.Second),
},
Txt: []string{txt},
})
}
}
return records
}
// 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
}
// 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 := 65533 // 64k - 2 bytes
// In order to compute properly, we have to avoid compress first
compressed := resp.Compress
resp.Compress = false
// 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)
// Beyond 2500 records, performance gets bad
// Limit the number of records at once, anyway, it won't fit in 64k
// For SRV Records, the max is around 500 records, for A, less than 2k
truncateAt := 2048
if req.Question[0].Qtype == dns.TypeSRV {
truncateAt = 640
}
if len(resp.Answer) > truncateAt {
resp.Answer = resp.Answer[:truncateAt]
}
if hasExtra {
index = make(map[string]dns.RR, len(resp.Extra))
indexRRs(resp.Extra, index)
}
truncated := false
// This enforces the given limit on 64k, the max limit for DNS messages
for len(resp.Answer) > 0 && resp.Len() > maxSize {
truncated = true
resp.Answer = resp.Answer[:len(resp.Answer)-1]
if hasExtra {
syncExtra(index, resp)
}
}
if truncated {
d.logger.Printf("[DEBUG] dns: TCP answer to %v too large truncated recs:=%d/%d, size:=%d/%d",
req.Question,
len(resp.Answer), originalNumRecords, resp.Len(), originalSize)
}
// Restore compression if any
resp.Compress = compressed
return truncated
}
// trimUDPResponse makes sure a UDP response is not longer than allowed by RFC
// 1035. Enforce an arbitrary limit that can be further ratcheted down by
// config, and then make sure the response doesn't exceed 512 bytes. Any extra
// records will be trimmed along with answers.
func trimUDPResponse(req, resp *dns.Msg, udpAnswerLimit int) (trimmed bool) {
numAnswers := len(resp.Answer)
hasExtra := len(resp.Extra) > 0
maxSize := defaultMaxUDPSize
// Update to the maximum edns size
if edns := req.IsEdns0(); edns != nil {
if size := edns.UDPSize(); size > uint16(maxSize) {
maxSize = int(size)
}
}
// We avoid some function calls and allocations by only handling the
// extra data when necessary.
var index map[string]dns.RR
if hasExtra {
index = make(map[string]dns.RR, len(resp.Extra))
indexRRs(resp.Extra, index)
}
// This cuts UDP responses to a useful but limited number of responses.
maxAnswers := lib.MinInt(maxUDPAnswerLimit, udpAnswerLimit)
if maxSize == defaultMaxUDPSize && numAnswers > maxAnswers {
resp.Answer = resp.Answer[:maxAnswers]
if hasExtra {
syncExtra(index, resp)
}
}
// This enforces the given limit on the number bytes. The default is 512 as
// per the RFC, but EDNS0 allows for the user to specify larger sizes. Note
// that we temporarily switch to uncompressed so that we limit to a response
// that will not exceed 512 bytes uncompressed, which is more conservative and
// will allow our responses to be compliant even if some downstream server
// uncompresses them.
compress := resp.Compress
resp.Compress = false
for len(resp.Answer) > 0 && resp.Len() > maxSize {
resp.Answer = resp.Answer[:len(resp.Answer)-1]
if hasExtra {
syncExtra(index, resp)
}
}
resp.Compress = compress
return len(resp.Answer) < numAnswers
}
// trimDNSResponse will trim the response for UDP and TCP
func (d *DNSServer) trimDNSResponse(network string, req, resp *dns.Msg) (trimmed bool) {
if network != "tcp" {
trimmed = trimUDPResponse(req, resp, d.config.UDPAnswerLimit)
} else {
trimmed = d.trimTCPResponse(req, resp)
}
// Flag that there are more records to return in the UDP response
if trimmed && d.config.EnableTruncate {
resp.Truncated = true
}
return trimmed
}
// lookupServiceNodes returns nodes with a given service.
func (d *DNSServer) lookupServiceNodes(datacenter, service, tag string) (structs.IndexedCheckServiceNodes, error) {
args := structs.ServiceSpecificRequest{
Datacenter: datacenter,
ServiceName: service,
ServiceTag: tag,
TagFilter: tag != "",
QueryOptions: structs.QueryOptions{
Token: d.agent.tokens.UserToken(),
AllowStale: d.config.AllowStale,
},
}
var out structs.IndexedCheckServiceNodes
if err := d.agent.RPC("Health.ServiceNodes", &args, &out); err != nil {
return structs.IndexedCheckServiceNodes{}, err
}
if args.AllowStale && out.LastContact > staleCounterThreshold {
metrics.IncrCounter([]string{"consul", "dns", "stale_queries"}, 1)
metrics.IncrCounter([]string{"dns", "stale_queries"}, 1)
}
// redo the request the response was too stale
if args.AllowStale && out.LastContact > d.config.MaxStale {
args.AllowStale = false
d.logger.Printf("[WARN] dns: Query results too stale, re-requesting")
if err := d.agent.RPC("Health.ServiceNodes", &args, &out); err != nil {
return structs.IndexedCheckServiceNodes{}, err
}
}
// Filter out any service nodes due to health checks
out.Nodes = out.Nodes.Filter(d.config.OnlyPassing)
return out, nil
}
// serviceLookup is used to handle a service query
func (d *DNSServer) serviceLookup(network, datacenter, service, tag string, req, resp *dns.Msg) {
out, err := d.lookupServiceNodes(datacenter, service, tag)
if err != nil {
d.logger.Printf("[ERR] dns: rpc error: %v", err)
resp.SetRcode(req, dns.RcodeServerFailure)
return
}
// If we have no nodes, return not found!
if len(out.Nodes) == 0 {
d.addSOA(resp)
resp.SetRcode(req, dns.RcodeNameError)
return
}
// Perform a random shuffle
out.Nodes.Shuffle()
// Determine the TTL
var ttl time.Duration
if d.config.ServiceTTL != nil {
var ok bool
ttl, ok = d.config.ServiceTTL[service]
if !ok {
ttl = d.config.ServiceTTL["*"]
}
}
// Add various responses depending on the request
qType := req.Question[0].Qtype
if qType == dns.TypeSRV {
d.serviceSRVRecords(datacenter, out.Nodes, req, resp, ttl)
} else {
d.serviceNodeRecords(datacenter, out.Nodes, req, resp, ttl)
}
d.trimDNSResponse(network, req, resp)
// If the answer is empty and the response isn't truncated, return not found
if len(resp.Answer) == 0 && !resp.Truncated {
d.addSOA(resp)
return
}
}
func ednsSubnetForRequest(req *dns.Msg) *dns.EDNS0_SUBNET {
// IsEdns0 returns the EDNS RR if present or nil otherwise
edns := req.IsEdns0()
if edns == nil {
return nil
}
for _, o := range edns.Option {
if subnet, ok := o.(*dns.EDNS0_SUBNET); ok {
return subnet
}
}
return nil
}
// preparedQueryLookup is used to handle a prepared query.
func (d *DNSServer) preparedQueryLookup(network, datacenter, query string, remoteAddr net.Addr, req, resp *dns.Msg) {
// Execute the prepared query.
args := structs.PreparedQueryExecuteRequest{
Datacenter: datacenter,
QueryIDOrName: query,
QueryOptions: structs.QueryOptions{
Token: d.agent.tokens.UserToken(),
AllowStale: d.config.AllowStale,
},
// Always pass the local agent through. In the DNS interface, there
// is no provision for passing additional query parameters, so we
// send the local agent's data through to allow distance sorting
// relative to ourself on the server side.
Agent: structs.QuerySource{
Datacenter: d.agent.config.Datacenter,
Segment: d.agent.config.SegmentName,
Node: d.agent.config.NodeName,
},
}
subnet := ednsSubnetForRequest(req)
if subnet != nil {
args.Source.Ip = subnet.Address.String()
} else {
switch v := remoteAddr.(type) {
case *net.UDPAddr:
args.Source.Ip = v.IP.String()
case *net.TCPAddr:
args.Source.Ip = v.IP.String()
case *net.IPAddr:
args.Source.Ip = v.IP.String()
}
}
// TODO (slackpad) - What's a safe limit we can set here? It seems like
// with dup filtering done at this level we need to get everything to
// match the previous behavior. We can optimize by pushing more filtering
// into the query execution, but for now I think we need to get the full
// response. We could also choose a large arbitrary number that will
// likely work in practice, like 10*maxUDPAnswerLimit which should help
// reduce bandwidth if there are thousands of nodes available.
var out structs.PreparedQueryExecuteResponse
RPC:
if err := d.agent.RPC("PreparedQuery.Execute", &args, &out); err != nil {
// If they give a bogus query name, treat that as a name error,
// not a full on server error. We have to use a string compare
// here since the RPC layer loses the type information.
if err.Error() == consul.ErrQueryNotFound.Error() {
d.addSOA(resp)
resp.SetRcode(req, dns.RcodeNameError)
return
}
d.logger.Printf("[ERR] dns: rpc error: %v", err)
resp.SetRcode(req, dns.RcodeServerFailure)
return
}
// Verify that request is not too stale, redo the request.
if args.AllowStale {
if out.LastContact > d.config.MaxStale {
args.AllowStale = false
d.logger.Printf("[WARN] dns: Query results too stale, re-requesting")
goto RPC
} else if out.LastContact > staleCounterThreshold {
metrics.IncrCounter([]string{"consul", "dns", "stale_queries"}, 1)
metrics.IncrCounter([]string{"dns", "stale_queries"}, 1)
}
}
// Determine the TTL. The parse should never fail since we vet it when
// the query is created, but we check anyway. If the query didn't
// specify a TTL then we will try to use the agent's service-specific
// TTL configs.
var ttl time.Duration
if out.DNS.TTL != "" {
var err error
ttl, err = time.ParseDuration(out.DNS.TTL)
if err != nil {
d.logger.Printf("[WARN] dns: Failed to parse TTL '%s' for prepared query '%s', ignoring", out.DNS.TTL, query)
}
} else if d.config.ServiceTTL != nil {
var ok bool
ttl, ok = d.config.ServiceTTL[out.Service]
if !ok {
ttl = d.config.ServiceTTL["*"]
}
}
// If we have no nodes, return not found!
if len(out.Nodes) == 0 {
d.addSOA(resp)
resp.SetRcode(req, dns.RcodeNameError)
return
}
// Add various responses depending on the request.
qType := req.Question[0].Qtype
if qType == dns.TypeSRV {
d.serviceSRVRecords(out.Datacenter, out.Nodes, req, resp, ttl)
} else {
d.serviceNodeRecords(out.Datacenter, out.Nodes, req, resp, ttl)
}
d.trimDNSResponse(network, req, resp)
// If the answer is empty and the response isn't truncated, return not found
if len(resp.Answer) == 0 && !resp.Truncated {
d.addSOA(resp)
return
}
}
// serviceNodeRecords is used to add the node records for a service lookup
func (d *DNSServer) serviceNodeRecords(dc string, nodes structs.CheckServiceNodes, req, resp *dns.Msg, ttl time.Duration) {
qName := req.Question[0].Name
qType := req.Question[0].Qtype
handled := make(map[string]struct{})
edns := req.IsEdns0() != nil
count := 0
for _, node := range nodes {
// Start with the translated address but use the service address,
// if specified.
addr := d.agent.TranslateAddress(dc, node.Node.Address, node.Node.TaggedAddresses)
if node.Service.Address != "" {
addr = node.Service.Address
}
// If the service address is a CNAME for the service we are looking
// for then use the node address.
if qName == strings.TrimSuffix(addr, ".")+"." {
addr = node.Node.Address
}
// Avoid duplicate entries, possible if a node has
// the same service on multiple ports, etc.
if _, ok := handled[addr]; ok {
continue
}
handled[addr] = struct{}{}
// Add the node record
records := d.formatNodeRecord(node.Node, addr, qName, qType, ttl, edns)
if records != nil {
resp.Answer = append(resp.Answer, records...)
count++
if count == d.config.ARecordLimit {
// We stop only if greater than 0 or we reached the limit
return
}
}
}
}
// serviceARecords is used to add the SRV records for a service lookup
func (d *DNSServer) serviceSRVRecords(dc string, nodes structs.CheckServiceNodes, req, resp *dns.Msg, ttl time.Duration) {
handled := make(map[string]struct{})
edns := req.IsEdns0() != nil
for _, node := range nodes {
// Avoid duplicate entries, possible if a node has
// the same service the same port, etc.
tuple := fmt.Sprintf("%s:%s:%d", node.Node.Node, node.Service.Address, node.Service.Port)
if _, ok := handled[tuple]; ok {
continue
}
handled[tuple] = struct{}{}
// Add the SRV record
srvRec := &dns.SRV{
Hdr: dns.RR_Header{
Name: req.Question[0].Name,
Rrtype: dns.TypeSRV,
Class: dns.ClassINET,
Ttl: uint32(ttl / time.Second),
},
Priority: 1,
Weight: 1,
Port: uint16(node.Service.Port),
Target: fmt.Sprintf("%s.node.%s.%s", node.Node.Node, dc, d.domain),
}
resp.Answer = append(resp.Answer, srvRec)
// Start with the translated address but use the service address,
// if specified.
addr := d.agent.TranslateAddress(dc, node.Node.Address, node.Node.TaggedAddresses)
if node.Service.Address != "" {
addr = node.Service.Address
}
// Add the extra record
records := d.formatNodeRecord(node.Node, addr, srvRec.Target, dns.TypeANY, ttl, edns)
if len(records) > 0 {
// Use the node address if it doesn't differ from the service address
if addr == node.Node.Address {
resp.Extra = append(resp.Extra, records...)
} else {
// If it differs from the service address, give a special response in the
// 'addr.consul' domain with the service IP encoded in it. We have to do
// this because we can't put an IP in the target field of an SRV record.
switch record := records[0].(type) {
// IPv4
case *dns.A:
addr := hex.EncodeToString(record.A)
// Take the last 8 chars (4 bytes) of the encoded address to avoid junk bytes
srvRec.Target = fmt.Sprintf("%s.addr.%s.%s", addr[len(addr)-(net.IPv4len*2):], dc, d.domain)
record.Hdr.Name = srvRec.Target
resp.Extra = append(resp.Extra, record)
// IPv6
case *dns.AAAA:
srvRec.Target = fmt.Sprintf("%s.addr.%s.%s", hex.EncodeToString(record.AAAA), dc, d.domain)
record.Hdr.Name = srvRec.Target
resp.Extra = append(resp.Extra, record)
// Something else (probably a CNAME; just add the records).
default:
resp.Extra = append(resp.Extra, records...)
}
}
}
}
}
// handleRecurse is used to handle recursive DNS queries
func (d *DNSServer) handleRecurse(resp dns.ResponseWriter, req *dns.Msg) {
q := req.Question[0]
network := "udp"
defer func(s time.Time) {
d.logger.Printf("[DEBUG] dns: request for %v (%s) (%v) from client %s (%s)",
q, network, time.Since(s), resp.RemoteAddr().String(),
resp.RemoteAddr().Network())
}(time.Now())
// Switch to TCP if the client is
if _, ok := resp.RemoteAddr().(*net.TCPAddr); ok {
network = "tcp"
}
// Recursively resolve
c := &dns.Client{Net: network, Timeout: d.config.RecursorTimeout}
var r *dns.Msg
var rtt time.Duration
var err error
for _, recursor := range d.recursors {
r, rtt, err = c.Exchange(req, recursor)
if err == nil || err == dns.ErrTruncated {
// Compress the response; we don't know if the incoming
// response was compressed or not, so by not compressing
// we might generate an invalid packet on the way out.
r.Compress = !d.disableCompression.Load().(bool)
// Forward the response
d.logger.Printf("[DEBUG] dns: recurse RTT for %v (%v)", q, rtt)
if err := resp.WriteMsg(r); err != nil {
d.logger.Printf("[WARN] dns: failed to respond: %v", err)
}
return
}
d.logger.Printf("[ERR] dns: recurse failed: %v", err)
}
// If all resolvers fail, return a SERVFAIL message
d.logger.Printf("[ERR] dns: all resolvers failed for %v from client %s (%s)",
q, resp.RemoteAddr().String(), resp.RemoteAddr().Network())
m := &dns.Msg{}
m.SetReply(req)
m.Compress = !d.disableCompression.Load().(bool)
m.RecursionAvailable = true
m.SetRcode(req, dns.RcodeServerFailure)
if edns := req.IsEdns0(); edns != nil {
m.SetEdns0(edns.UDPSize(), false)
}
resp.WriteMsg(m)
}
// resolveCNAME is used to recursively resolve CNAME records
func (d *DNSServer) resolveCNAME(name string) []dns.RR {
// If the CNAME record points to a Consul address, resolve it internally
// Convert query to lowercase because DNS is case insensitive; d.domain is
// already converted
if strings.HasSuffix(strings.ToLower(name), "."+d.domain) {
req := &dns.Msg{}
resp := &dns.Msg{}
req.SetQuestion(name, dns.TypeANY)
d.dispatch("udp", nil, req, resp)
return resp.Answer
}
// Do nothing if we don't have a recursor
if len(d.recursors) == 0 {
return nil
}
// Ask for any A records
m := new(dns.Msg)
m.SetQuestion(name, dns.TypeA)
// Make a DNS lookup request
c := &dns.Client{Net: "udp", Timeout: d.config.RecursorTimeout}
var r *dns.Msg
var rtt time.Duration
var err error
for _, recursor := range d.recursors {
r, rtt, err = c.Exchange(m, recursor)
if err == nil {
d.logger.Printf("[DEBUG] dns: cname recurse RTT for %v (%v)", name, rtt)
return r.Answer
}
d.logger.Printf("[ERR] dns: cname recurse failed for %v: %v", name, err)
}
d.logger.Printf("[ERR] dns: all resolvers failed for %v", name)
return nil
}