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-rw-r--r--plugin/loadbalance/README.md22
-rw-r--r--plugin/loadbalance/handler.go23
-rw-r--r--plugin/loadbalance/loadbalance.go87
-rw-r--r--plugin/loadbalance/loadbalance_test.go168
-rw-r--r--plugin/loadbalance/setup.go26
5 files changed, 326 insertions, 0 deletions
diff --git a/plugin/loadbalance/README.md b/plugin/loadbalance/README.md
new file mode 100644
index 000000000..1cce54ebf
--- /dev/null
+++ b/plugin/loadbalance/README.md
@@ -0,0 +1,22 @@
+# loadbalance
+
+*loadbalance* acts as a round-robin DNS loadbalancer by randomizing the order of A and AAAA records
+ in the answer.
+
+ See [Wikipedia](https://en.wikipedia.org/wiki/Round-robin_DNS) about the pros and cons on this
+ setup. It will take care to sort any CNAMEs before any address records, because some stub resolver
+ implementations (like glibc) are particular about that.
+
+## Syntax
+
+~~~
+loadbalance [POLICY]
+~~~
+
+* **POLICY** is how to balance, the default is "round_robin"
+
+## Examples
+
+~~~
+loadbalance round_robin
+~~~
diff --git a/plugin/loadbalance/handler.go b/plugin/loadbalance/handler.go
new file mode 100644
index 000000000..da4cf1549
--- /dev/null
+++ b/plugin/loadbalance/handler.go
@@ -0,0 +1,23 @@
+// Package loadbalance is plugin for rewriting responses to do "load balancing"
+package loadbalance
+
+import (
+ "github.com/coredns/coredns/plugin"
+
+ "github.com/miekg/dns"
+ "golang.org/x/net/context"
+)
+
+// RoundRobin is plugin to rewrite responses for "load balancing".
+type RoundRobin struct {
+ Next plugin.Handler
+}
+
+// ServeDNS implements the plugin.Handler interface.
+func (rr RoundRobin) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
+ wrr := &RoundRobinResponseWriter{w}
+ return plugin.NextOrFailure(rr.Name(), rr.Next, ctx, wrr, r)
+}
+
+// Name implements the Handler interface.
+func (rr RoundRobin) Name() string { return "loadbalance" }
diff --git a/plugin/loadbalance/loadbalance.go b/plugin/loadbalance/loadbalance.go
new file mode 100644
index 000000000..7df0b31c6
--- /dev/null
+++ b/plugin/loadbalance/loadbalance.go
@@ -0,0 +1,87 @@
+// Package loadbalance shuffles A and AAAA records.
+package loadbalance
+
+import (
+ "log"
+
+ "github.com/miekg/dns"
+)
+
+// RoundRobinResponseWriter is a response writer that shuffles A and AAAA records.
+type RoundRobinResponseWriter struct {
+ dns.ResponseWriter
+}
+
+// WriteMsg implements the dns.ResponseWriter interface.
+func (r *RoundRobinResponseWriter) WriteMsg(res *dns.Msg) error {
+ if res.Rcode != dns.RcodeSuccess {
+ return r.ResponseWriter.WriteMsg(res)
+ }
+
+ res.Answer = roundRobin(res.Answer)
+ res.Ns = roundRobin(res.Ns)
+ res.Extra = roundRobin(res.Extra)
+
+ return r.ResponseWriter.WriteMsg(res)
+}
+
+func roundRobin(in []dns.RR) []dns.RR {
+ cname := []dns.RR{}
+ address := []dns.RR{}
+ mx := []dns.RR{}
+ rest := []dns.RR{}
+ for _, r := range in {
+ switch r.Header().Rrtype {
+ case dns.TypeCNAME:
+ cname = append(cname, r)
+ case dns.TypeA, dns.TypeAAAA:
+ address = append(address, r)
+ case dns.TypeMX:
+ mx = append(mx, r)
+ default:
+ rest = append(rest, r)
+ }
+ }
+
+ roundRobinShuffle(address)
+ roundRobinShuffle(mx)
+
+ out := append(cname, rest...)
+ out = append(out, address...)
+ out = append(out, mx...)
+ return out
+}
+
+func roundRobinShuffle(records []dns.RR) {
+ switch l := len(records); l {
+ case 0, 1:
+ break
+ case 2:
+ if dns.Id()%2 == 0 {
+ records[0], records[1] = records[1], records[0]
+ }
+ default:
+ for j := 0; j < l*(int(dns.Id())%4+1); j++ {
+ q := int(dns.Id()) % l
+ p := int(dns.Id()) % l
+ if q == p {
+ p = (p + 1) % l
+ }
+ records[q], records[p] = records[p], records[q]
+ }
+ }
+}
+
+// Write implements the dns.ResponseWriter interface.
+func (r *RoundRobinResponseWriter) Write(buf []byte) (int, error) {
+ // Should we pack and unpack here to fiddle with the packet... Not likely.
+ log.Printf("[WARNING] RoundRobin called with Write: no shuffling records")
+ n, err := r.ResponseWriter.Write(buf)
+ return n, err
+}
+
+// Hijack implements the dns.ResponseWriter interface.
+func (r *RoundRobinResponseWriter) Hijack() {
+ r.ResponseWriter.Hijack()
+ return
+}
diff --git a/plugin/loadbalance/loadbalance_test.go b/plugin/loadbalance/loadbalance_test.go
new file mode 100644
index 000000000..bde92b543
--- /dev/null
+++ b/plugin/loadbalance/loadbalance_test.go
@@ -0,0 +1,168 @@
+package loadbalance
+
+import (
+ "testing"
+
+ "github.com/coredns/coredns/plugin"
+ "github.com/coredns/coredns/plugin/pkg/dnsrecorder"
+ "github.com/coredns/coredns/plugin/test"
+
+ "github.com/miekg/dns"
+ "golang.org/x/net/context"
+)
+
+func TestLoadBalance(t *testing.T) {
+ rm := RoundRobin{Next: handler()}
+
+ // the first X records must be cnames after this test
+ tests := []struct {
+ answer []dns.RR
+ extra []dns.RR
+ cnameAnswer int
+ cnameExtra int
+ addressAnswer int
+ addressExtra int
+ mxAnswer int
+ mxExtra int
+ }{
+ {
+ answer: []dns.RR{
+ test.CNAME("cname1.region2.skydns.test. 300 IN CNAME cname2.region2.skydns.test."),
+ test.CNAME("cname2.region2.skydns.test. 300 IN CNAME cname3.region2.skydns.test."),
+ test.CNAME("cname5.region2.skydns.test. 300 IN CNAME cname6.region2.skydns.test."),
+ test.CNAME("cname6.region2.skydns.test. 300 IN CNAME endpoint.region2.skydns.test."),
+ test.A("endpoint.region2.skydns.test. 300 IN A 10.240.0.1"),
+ test.MX("mx.region2.skydns.test. 300 IN MX 1 mx1.region2.skydns.test."),
+ test.MX("mx.region2.skydns.test. 300 IN MX 2 mx2.region2.skydns.test."),
+ test.MX("mx.region2.skydns.test. 300 IN MX 3 mx3.region2.skydns.test."),
+ },
+ cnameAnswer: 4,
+ addressAnswer: 1,
+ mxAnswer: 3,
+ },
+ {
+ answer: []dns.RR{
+ test.A("endpoint.region2.skydns.test. 300 IN A 10.240.0.1"),
+ test.MX("mx.region2.skydns.test. 300 IN MX 1 mx1.region2.skydns.test."),
+ test.CNAME("cname.region2.skydns.test. 300 IN CNAME endpoint.region2.skydns.test."),
+ },
+ cnameAnswer: 1,
+ addressAnswer: 1,
+ mxAnswer: 1,
+ },
+ {
+ answer: []dns.RR{
+ test.MX("mx.region2.skydns.test. 300 IN MX 1 mx1.region2.skydns.test."),
+ test.A("endpoint.region2.skydns.test. 300 IN A 10.240.0.1"),
+ test.A("endpoint.region2.skydns.test. 300 IN A 10.240.0.2"),
+ test.MX("mx.region2.skydns.test. 300 IN MX 1 mx2.region2.skydns.test."),
+ test.CNAME("cname2.region2.skydns.test. 300 IN CNAME cname3.region2.skydns.test."),
+ test.A("endpoint.region2.skydns.test. 300 IN A 10.240.0.3"),
+ test.MX("mx.region2.skydns.test. 300 IN MX 1 mx3.region2.skydns.test."),
+ },
+ extra: []dns.RR{
+ test.A("endpoint.region2.skydns.test. 300 IN A 10.240.0.1"),
+ test.AAAA("endpoint.region2.skydns.test. 300 IN AAAA ::1"),
+ test.MX("mx.region2.skydns.test. 300 IN MX 1 mx1.region2.skydns.test."),
+ test.CNAME("cname2.region2.skydns.test. 300 IN CNAME cname3.region2.skydns.test."),
+ test.MX("mx.region2.skydns.test. 300 IN MX 1 mx2.region2.skydns.test."),
+ test.A("endpoint.region2.skydns.test. 300 IN A 10.240.0.3"),
+ test.AAAA("endpoint.region2.skydns.test. 300 IN AAAA ::2"),
+ test.MX("mx.region2.skydns.test. 300 IN MX 1 mx3.region2.skydns.test."),
+ },
+ cnameAnswer: 1,
+ cnameExtra: 1,
+ addressAnswer: 3,
+ addressExtra: 4,
+ mxAnswer: 3,
+ mxExtra: 3,
+ },
+ }
+
+ rec := dnsrecorder.New(&test.ResponseWriter{})
+
+ for i, test := range tests {
+ req := new(dns.Msg)
+ req.SetQuestion("region2.skydns.test.", dns.TypeSRV)
+ req.Answer = test.answer
+ req.Extra = test.extra
+
+ _, err := rm.ServeDNS(context.TODO(), rec, req)
+ if err != nil {
+ t.Errorf("Test %d: Expected no error, but got %s", i, err)
+ continue
+
+ }
+
+ cname, address, mx, sorted := countRecords(rec.Msg.Answer)
+ if !sorted {
+ t.Errorf("Test %d: Expected CNAMEs, then AAAAs, then MX in Answer, but got mixed", i)
+ }
+ if cname != test.cnameAnswer {
+ t.Errorf("Test %d: Expected %d CNAMEs in Answer, but got %d", i, test.cnameAnswer, cname)
+ }
+ if address != test.addressAnswer {
+ t.Errorf("Test %d: Expected %d A/AAAAs in Answer, but got %d", i, test.addressAnswer, address)
+ }
+ if mx != test.mxAnswer {
+ t.Errorf("Test %d: Expected %d MXs in Answer, but got %d", i, test.mxAnswer, mx)
+ }
+
+ cname, address, mx, sorted = countRecords(rec.Msg.Extra)
+ if !sorted {
+ t.Errorf("Test %d: Expected CNAMEs, then AAAAs, then MX in Extra, but got mixed", i)
+ }
+ if cname != test.cnameExtra {
+ t.Errorf("Test %d: Expected %d CNAMEs in Extra, but got %d", i, test.cnameAnswer, cname)
+ }
+ if address != test.addressExtra {
+ t.Errorf("Test %d: Expected %d A/AAAAs in Extra, but got %d", i, test.addressAnswer, address)
+ }
+ if mx != test.mxExtra {
+ t.Errorf("Test %d: Expected %d MXs in Extra, but got %d", i, test.mxAnswer, mx)
+ }
+ }
+}
+
+func countRecords(result []dns.RR) (cname int, address int, mx int, sorted bool) {
+ const (
+ Start = iota
+ CNAMERecords
+ ARecords
+ MXRecords
+ Any
+ )
+
+ // The order of the records is used to determine if the round-robin actually did anything.
+ sorted = true
+ cname = 0
+ address = 0
+ mx = 0
+ state := Start
+ for _, r := range result {
+ switch r.Header().Rrtype {
+ case dns.TypeCNAME:
+ sorted = sorted && state <= CNAMERecords
+ state = CNAMERecords
+ cname++
+ case dns.TypeA, dns.TypeAAAA:
+ sorted = sorted && state <= ARecords
+ state = ARecords
+ address++
+ case dns.TypeMX:
+ sorted = sorted && state <= MXRecords
+ state = MXRecords
+ mx++
+ default:
+ state = Any
+ }
+ }
+ return
+}
+
+func handler() plugin.Handler {
+ return plugin.HandlerFunc(func(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
+ w.WriteMsg(r)
+ return dns.RcodeSuccess, nil
+ })
+}
diff --git a/plugin/loadbalance/setup.go b/plugin/loadbalance/setup.go
new file mode 100644
index 000000000..c2d90958e
--- /dev/null
+++ b/plugin/loadbalance/setup.go
@@ -0,0 +1,26 @@
+package loadbalance
+
+import (
+ "github.com/coredns/coredns/core/dnsserver"
+ "github.com/coredns/coredns/plugin"
+ "github.com/mholt/caddy"
+)
+
+func init() {
+ caddy.RegisterPlugin("loadbalance", caddy.Plugin{
+ ServerType: "dns",
+ Action: setup,
+ })
+}
+
+func setup(c *caddy.Controller) error {
+ for c.Next() {
+ // TODO(miek): block and option parsing
+ }
+
+ dnsserver.GetConfig(c).AddPlugin(func(next plugin.Handler) plugin.Handler {
+ return RoundRobin{Next: next}
+ })
+
+ return nil
+}
generated by cgit v1.2.3 (git 2.39.1) at 2025-07-25 03:04:08 +0000