7da2cedaf0
* Add weighted-round-robin policy to loadbalance plugin Signed-off-by: Gabor Dozsa <gabor.dozsa@ibm.com>
91 lines
2.1 KiB
Go
91 lines
2.1 KiB
Go
// Package loadbalance shuffles A, AAAA and MX records.
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package loadbalance
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import (
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"github.com/miekg/dns"
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)
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const (
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ramdomShufflePolicy = "round_robin"
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weightedRoundRobinPolicy = "weighted"
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)
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// LoadBalanceResponseWriter is a response writer that shuffles A, AAAA and MX records.
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type LoadBalanceResponseWriter struct {
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dns.ResponseWriter
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shuffle func(*dns.Msg) *dns.Msg
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}
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// WriteMsg implements the dns.ResponseWriter interface.
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func (r *LoadBalanceResponseWriter) WriteMsg(res *dns.Msg) error {
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if res.Rcode != dns.RcodeSuccess {
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return r.ResponseWriter.WriteMsg(res)
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}
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if res.Question[0].Qtype == dns.TypeAXFR || res.Question[0].Qtype == dns.TypeIXFR {
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return r.ResponseWriter.WriteMsg(res)
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}
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return r.ResponseWriter.WriteMsg(r.shuffle(res))
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}
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func randomShuffle(res *dns.Msg) *dns.Msg {
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res.Answer = roundRobin(res.Answer)
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res.Ns = roundRobin(res.Ns)
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res.Extra = roundRobin(res.Extra)
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return res
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}
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func roundRobin(in []dns.RR) []dns.RR {
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cname := []dns.RR{}
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address := []dns.RR{}
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mx := []dns.RR{}
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rest := []dns.RR{}
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for _, r := range in {
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switch r.Header().Rrtype {
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case dns.TypeCNAME:
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cname = append(cname, r)
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case dns.TypeA, dns.TypeAAAA:
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address = append(address, r)
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case dns.TypeMX:
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mx = append(mx, r)
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default:
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rest = append(rest, r)
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}
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}
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roundRobinShuffle(address)
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roundRobinShuffle(mx)
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out := append(cname, rest...)
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out = append(out, address...)
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out = append(out, mx...)
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return out
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}
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func roundRobinShuffle(records []dns.RR) {
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switch l := len(records); l {
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case 0, 1:
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break
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case 2:
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if dns.Id()%2 == 0 {
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records[0], records[1] = records[1], records[0]
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}
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default:
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for j := 0; j < l; j++ {
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p := j + (int(dns.Id()) % (l - j))
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if j == p {
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continue
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}
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records[j], records[p] = records[p], records[j]
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}
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}
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}
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// Write implements the dns.ResponseWriter interface.
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func (r *LoadBalanceResponseWriter) Write(buf []byte) (int, error) {
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// Should we pack and unpack here to fiddle with the packet... Not likely.
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log.Warning("LoadBalance called with Write: not shuffling records")
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n, err := r.ResponseWriter.Write(buf)
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return n, err
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}
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