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Allow adjusting the number of DNS records in a response... 

Based on work done by @fusiondog in #1583, extend the concept to use an integer instead of a boolean.

Fixes: #1583 && #1481
This commit is contained in:
Sean Chittenden 2016-02-11 23:58:48 -08:00
parent 6b665d3ddb
commit d2745081f3
8 changed files with 190 additions and 38 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
command/agent/command.go
View File

@ -189,6 +189,11 @@ func (c *Command) readConfig() *Config {
}
}
// Verify DNS settings
if config.DNSConfig.UDPAnswerLimit < 1 {
c.Ui.Error(fmt.Sprintf("dns_config.udp_answer_limit %d too low, must always be greater than zero", config.DNSConfig.UDPAnswerLimit))
}
if config.EncryptKey != "" {
if _, err := config.EncryptBytes(); err != nil {
c.Ui.Error(fmt.Sprintf("Invalid encryption key: %s", err))

26
command/agent/config.go
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@ -77,13 +77,16 @@ type DNSConfig struct {
// returned by default for UDP.
EnableTruncate bool `mapstructure:"enable_truncate"`
// EnableSingleton is used to override default behavior
// of DNS and return only a single host in a round robin
// DNS service request rather than all healthy service
// members. This is a work around for systems using
// getaddrinfo using rule 9 sorting from RFC3484 which
// breaks round robin DNS.
EnableSingleton bool `mapstructure:"enable_singleton"`
// UDPAnswerLimit is used to limit the maximum number of DNS Resource
// Records returned in the ANSWER section of a DNS response. This is
// not normally useful and will be limited based on the querying
// protocol, however systems that implemented §6 Rule 9 in RFC3484
// may want to set this to 1 in order to achieve round-robin DNS.
// RFC3484 sorts answers in a deterministic order, which defeats the
// purpose of round-robin DNS. This RFC has been obsoleted by
// RFC6724, however a large number of Linux hosts using glibc(3)
// implemented §6 Rule 9 (e.g. CentOS 5-6, Debian Squeeze, etc).
UDPAnswerLimit int `mapstructure:"udp_answer_limit"`
// MaxStale is used to bound how stale of a result is
// accepted for a DNS lookup. This can be used with
@ -535,7 +538,8 @@ func DefaultConfig() *Config {
Server: 8300,
},
DNSConfig: DNSConfig{
MaxStale: 5 * time.Second,
UDPAnswerLimit: 3,
MaxStale: 5 * time.Second,
},
Telemetry: Telemetry{
StatsitePrefix: "consul",
@ -1135,12 +1139,12 @@ func MergeConfig(a, b *Config) *Config {
if b.DNSConfig.AllowStale {
result.DNSConfig.AllowStale = true
}
if b.DNSConfig.UDPAnswerLimit != 0 {
result.DNSConfig.UDPAnswerLimit = b.DNSConfig.UDPAnswerLimit
}
if b.DNSConfig.EnableTruncate {
result.DNSConfig.EnableTruncate = true
}
if b.DNSConfig.EnableSingleton {
result.DNSConfig.EnableSingleton = true
}
if b.DNSConfig.MaxStale != 0 {
result.DNSConfig.MaxStale = b.DNSConfig.MaxStale
}

9
command/agent/config_test.go
View File

@ -1252,13 +1252,14 @@ func TestMergeConfig(t *testing.T) {
DataDir: "/tmp/bar",
DNSRecursors: []string{"127.0.0.2:1001"},
DNSConfig: DNSConfig{
NodeTTL: 10 * time.Second,
AllowStale: false,
EnableTruncate: true,
MaxStale: 30 * time.Second,
NodeTTL: 10 * time.Second,
ServiceTTL: map[string]time.Duration{
"api": 10 * time.Second,
},
AllowStale: true,
MaxStale: 30 * time.Second,
EnableTruncate: true,
UDPAnswerLimit: 3,
},
Domain: "other",
LogLevel: "info",

24
command/agent/dns.go
View File

@ -12,12 +12,13 @@ import (
"github.com/armon/go-metrics"
"github.com/hashicorp/consul/consul"
"github.com/hashicorp/consul/consul/structs"
"github.com/hashicorp/consul/lib"
"github.com/miekg/dns"
)
const (
maxServiceResponses = 3 // For UDP only
maxRecurseRecords = 5
maxUDPAnswerLimit = 8 // For UDP only
maxRecurseRecords = 5
)
// DNSServer is used to wrap an Agent and expose various
@ -547,8 +548,8 @@ RPC:
}
// If the network is not TCP, restrict the number of responses
if network != "tcp" && len(resp.Answer) > maxServiceResponses {
resp.Answer = resp.Answer[:maxServiceResponses]
if network != "tcp" && len(resp.Answer) > maxUDPAnswerLimit {
resp.Answer = resp.Answer[:maxUDPAnswerLimit]
// Flag that there are more records to return in the UDP response
if d.config.EnableTruncate {
@ -580,7 +581,7 @@ func (d *DNSServer) preparedQueryLookup(network, datacenter, query string, req,
// 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*maxServiceResponses which should help
// likely work in practice, like 10*maxUDPAnswerLimit which should help
// reduce bandwidth if there are thousands of nodes available.
endpoint := d.agent.getEndpoint(preparedQueryEndpoint)
@ -642,8 +643,8 @@ RPC:
}
// If the network is not TCP, restrict the number of responses.
if network != "tcp" && len(resp.Answer) > maxServiceResponses {
resp.Answer = resp.Answer[:maxServiceResponses]
if network != "tcp" && len(resp.Answer) > maxUDPAnswerLimit {
resp.Answer = resp.Answer[:maxUDPAnswerLimit]
// Flag that there are more records to return in the UDP
// response.
@ -664,6 +665,9 @@ func (d *DNSServer) serviceNodeRecords(dc string, nodes structs.CheckServiceNode
qName := req.Question[0].Name
qType := req.Question[0].Qtype
handled := make(map[string]struct{})
// Post-shuffle: limit the number of nodes we return to the client
effectiveRecordLimit := lib.MinInt(d.config.UDPAnswerLimit, maxUDPAnswerLimit)
for _, node := range nodes {
// Start with the translated address but use the service address,
// if specified.
@ -684,7 +688,11 @@ func (d *DNSServer) serviceNodeRecords(dc string, nodes structs.CheckServiceNode
if records != nil {
resp.Answer = append(resp.Answer, records...)
}
if d.config.EnableSingleton {
if len(resp.Answer) >= effectiveRecordLimit {
if d.config.EnableTruncate {
resp.Truncated = true
}
break
}
}

110
command/agent/dns_test.go
View File

@ -13,6 +13,13 @@ import (
"github.com/miekg/dns"
)
const (
testUDPAnswerLimit = 4
testMaxUDPDNSResponses = 3
testGenerateNumNodes = 12
testUDPTruncateLimit = 8
)
func makeDNSServer(t *testing.T) (string, *DNSServer) {
return makeDNSServerConfig(t, nil, nil)
}
@ -26,7 +33,7 @@ func makeDNSServerConfig(
if agentFn != nil {
agentFn(agentConf)
}
dnsConf := &DNSConfig{}
dnsConf := &DefaultConfig().DNSConfig
if dnsFn != nil {
dnsFn(dnsConf)
}
@ -1809,7 +1816,7 @@ func TestDNS_ServiceLookup_Randomize(t *testing.T) {
testutil.WaitForLeader(t, srv.agent.RPC, "dc1")
// Register a large set of nodes.
for i := 0; i < 3*maxServiceResponses; i++ {
for i := 0; i < 2*testMaxUDPDNSResponses; i++ {
args := &structs.RegisterRequest{
Datacenter: "dc1",
Node: fmt.Sprintf("foo%d", i),
@ -1856,7 +1863,7 @@ func TestDNS_ServiceLookup_Randomize(t *testing.T) {
m := new(dns.Msg)
m.SetQuestion(question, dns.TypeANY)
c := new(dns.Client)
c := &dns.Client{Net: "udp"}
in, _, err := c.Exchange(m, addr.String())
if err != nil {
t.Fatalf("err: %v", err)
@ -1864,7 +1871,7 @@ func TestDNS_ServiceLookup_Randomize(t *testing.T) {
// Response length should be truncated and we should get
// an A record for each response.
if len(in.Answer) != maxServiceResponses {
if len(in.Answer) != testMaxUDPDNSResponses {
t.Fatalf("Bad: %#v", len(in.Answer))
}
@ -1903,7 +1910,7 @@ func TestDNS_ServiceLookup_Truncate(t *testing.T) {
testutil.WaitForLeader(t, srv.agent.RPC, "dc1")
// Register nodes a large number of nodes.
for i := 0; i < 3*maxServiceResponses; i++ {
for i := 0; i < 2*testUDPTruncateLimit; i++ {
args := &structs.RegisterRequest{
Datacenter: "dc1",
Node: fmt.Sprintf("foo%d", i),
@ -1962,16 +1969,18 @@ func TestDNS_ServiceLookup_Truncate(t *testing.T) {
}
func TestDNS_ServiceLookup_MaxResponses(t *testing.T) {
dir, srv := makeDNSServer(t)
dir, srv := makeDNSServerConfig(t, nil, func(c *DNSConfig) {
c.UDPAnswerLimit = testUDPAnswerLimit
})
defer os.RemoveAll(dir)
defer srv.agent.Shutdown()
testutil.WaitForLeader(t, srv.agent.RPC, "dc1")
// Register a large number of nodes.
for i := 0; i < 6*maxServiceResponses; i++ {
for i := 0; i < testUDPAnswerLimit*testMaxUDPDNSResponses; i++ {
nodeAddress := fmt.Sprintf("127.0.0.%d", i+1)
if i > 3 {
if i > (testUDPAnswerLimit * testMaxUDPDNSResponses / 2) {
nodeAddress = fmt.Sprintf("fe80::%d", i+1)
}
args := &structs.RegisterRequest{
@ -2012,7 +2021,7 @@ func TestDNS_ServiceLookup_MaxResponses(t *testing.T) {
"web.service.consul.",
id + ".query.consul.",
}
for _, question := range questions {
for i, question := range questions {
m := new(dns.Msg)
m.SetQuestion(question, dns.TypeANY)
@ -2023,8 +2032,8 @@ func TestDNS_ServiceLookup_MaxResponses(t *testing.T) {
t.Fatalf("err: %v", err)
}
if len(in.Answer) != 3 {
t.Fatalf("should receive 3 answers for ANY")
if len(in.Answer) != testUDPAnswerLimit {
t.Fatalf("should receive %d answers for ANY, received: %d", testUDPAnswerLimit, len(in.Answer))
}
m.SetQuestion(question, dns.TypeA)
@ -2033,8 +2042,8 @@ func TestDNS_ServiceLookup_MaxResponses(t *testing.T) {
t.Fatalf("err: %v", err)
}
if len(in.Answer) != 3 {
t.Fatalf("should receive 3 answers for A")
if len(in.Answer) != testUDPAnswerLimit {
t.Fatalf("%d: should receive %d answers for A, received: %d", i, testUDPAnswerLimit, len(in.Answer))
}
m.SetQuestion(question, dns.TypeAAAA)
@ -2043,8 +2052,79 @@ func TestDNS_ServiceLookup_MaxResponses(t *testing.T) {
t.Fatalf("err: %v", err)
}
if len(in.Answer) != 3 {
t.Fatalf("should receive 3 answers for AAAA")
if len(in.Answer) != testUDPAnswerLimit {
t.Fatalf("should receive %d answers for AAAA, received: %d", testUDPAnswerLimit, len(in.Answer))
}
}
}
func TestDNS_ServiceLookup_UDPAnswerLimit(t *testing.T) {
dir, srv := makeDNSServer(t)
defer os.RemoveAll(dir)
defer srv.agent.Shutdown()
testutil.WaitForLeader(t, srv.agent.RPC, "dc1")
// Register a large number of nodes.
for i := 0; i < testGenerateNumNodes*testMaxUDPDNSResponses; i++ {
nodeAddress := fmt.Sprintf("127.0.0.%d", i+1)
// Mix-in a few IPv6 addresses
if i > testGenerateNumNodes/2 {
nodeAddress = fmt.Sprintf("fe80::%d", i+1)
}
args := &structs.RegisterRequest{
Datacenter: "dc1",
Node: fmt.Sprintf("foo%d", i),
Address: nodeAddress,
Service: &structs.NodeService{
Service: "web",
Port: 8000,
},
}
var out struct{}
if err := srv.agent.RPC("Catalog.Register", args, &out); err != nil {
t.Fatalf("err: %v", err)
}
}
// Look up the service directly and via prepared query.
questions := []string{
"web.service.consul.",
}
for _, question := range questions {
m := new(dns.Msg)
m.SetQuestion(question, dns.TypeANY)
addr, _ := srv.agent.config.ClientListener("", srv.agent.config.Ports.DNS)
c := &dns.Client{Net: "udp"}
in, _, err := c.Exchange(m, addr.String())
if err != nil {
t.Fatalf("err: %v", err)
}
if len(in.Answer) != srv.agent.config.DNSConfig.UDPAnswerLimit {
t.Fatalf("%d/%d answers received for ANY", len(in.Answer), srv.agent.config.DNSConfig.UDPAnswerLimit)
}
m.SetQuestion(question, dns.TypeA)
in, _, err = c.Exchange(m, addr.String())
if err != nil {
t.Fatalf("err: %v", err)
}
if len(in.Answer) != srv.agent.config.DNSConfig.UDPAnswerLimit {
t.Fatalf("%d/%d answers for A", len(in.Answer), srv.agent.config.DNSConfig.UDPAnswerLimit)
}
m.SetQuestion(question, dns.TypeAAAA)
in, _, err = c.Exchange(m, addr.String())
if err != nil {
t.Fatalf("err: %v", err)
}
if len(in.Answer) != srv.agent.config.DNSConfig.UDPAnswerLimit {
t.Fatalf("%d/%d answers for AAAA", len(in.Answer), srv.agent.config.DNSConfig.UDPAnswerLimit)
}
}
}

15
lib/math.go Normal file
View File

@ -0,0 +1,15 @@
package lib
func MaxInt(a, b int) int {
if a > b {
return a
}
return b
}
func MinInt(a, b int) int {
if a > b {
return b
}
return a
}

27
lib/math_test.go Normal file
View File

@ -0,0 +1,27 @@
package lib
import (
"testing"
)
func TestMathMaxInt(t *testing.T) {
tests := [][3]int{{1, 2, 2}, {-1, 1, 1}, {2, 0, 2}}
for i, _ := range tests {
expected := tests[i][2]
actual := MaxInt(tests[i][0], tests[i][1])
if expected != actual {
t.Fatalf("in iteration %d expected %d, got %d", i, expected, actual)
}
}
}
func TestMathMinInt(t *testing.T) {
tests := [][3]int{{1, 2, 1}, {-1, 1, -1}, {2, 0, 0}}
for i, _ := range tests {
expected := tests[i][2]
actual := MinInt(tests[i][0], tests[i][1])
if expected != actual {
t.Fatalf("in iteration %d expected %d, got %d", i, expected, actual)
}
}
}

12
website/source/docs/agent/options.html.markdown
View File

@ -467,6 +467,18 @@ definitions support being updated during a reload.
nodes whose healthchecks are not passing will be excluded from DNS results. By default (or
if set to false), only nodes whose healthchecks are failing as critical will be excluded.
* <a name="udp_answer_limit"></a><a
href="#udp_answer_limit">`udp_answer_limit`</a> - Artificially limit the
number of resource records contained in the answer section of a UDP-based
DNS response. The default number of resource records returned is `3`. In
environments where
[RFC 3484 Section 6](https://tools.ietf.org/html/rfc3484#section-6) Rule 9
is implemented and enforced, clients may need to set this value to `1` to
preserve randomized DNS round-robin (note:
[https://tools.ietf.org/html/rfc3484](RFC 3484) has been obsoleted by
[RFC 6724](https://tools.ietf.org/html/rfc6724) so it should be uncommon to
need to change this value).
* <a name="domain"></a><a href="#domain">`domain`</a> Equivalent to the
[`-domain` command-line flag](#_domain).