558c34a23e
* middleware/proxy: add spray keyword When spray is used, the proxy will, when all backend are down, spray to each target. When not used, default to the old defaults: max 1 failure and no spray. These defaults are also used when forwarding queries to another CoreDNS instance. Update the README with the new keyword. * typos * Make MaxFail = 1 again * more reversals
113 lines
3 KiB
Go
113 lines
3 KiB
Go
package proxy
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import (
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"log"
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"math/rand"
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"sync/atomic"
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)
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// HostPool is a collection of UpstreamHosts.
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type HostPool []*UpstreamHost
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// Policy decides how a host will be selected from a pool. When all hosts are unhealthy, it is assumed the
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// healthchecking failed. In this case each policy will *randomly* return a host from the pool to prevent
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// no traffic to go through at all.
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type Policy interface {
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Select(pool HostPool) *UpstreamHost
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}
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func init() {
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RegisterPolicy("random", func() Policy { return &Random{} })
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RegisterPolicy("least_conn", func() Policy { return &LeastConn{} })
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RegisterPolicy("round_robin", func() Policy { return &RoundRobin{} })
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}
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// Random is a policy that selects up hosts from a pool at random.
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type Random struct{}
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// Select selects an up host at random from the specified pool.
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func (r *Random) Select(pool HostPool) *UpstreamHost {
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// instead of just generating a random index
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// this is done to prevent selecting a down host
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var randHost *UpstreamHost
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count := 0
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for _, host := range pool {
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if host.Down() {
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continue
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}
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count++
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if count == 1 {
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randHost = host
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} else {
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r := rand.Int() % count
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if r == (count - 1) {
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randHost = host
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}
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}
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}
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return randHost
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}
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// Spray is a policy that selects a host from a pool at random. This should be used as a last ditch
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// attempt to get a host when all hosts are reporting unhealthy.
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type Spray struct{}
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// Select selects an up host at random from the specified pool.
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func (r *Spray) Select(pool HostPool) *UpstreamHost {
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rnd := rand.Int() % len(pool)
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randHost := pool[rnd]
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log.Printf("[WARNING] All hosts reported as down, spraying to target: %s", randHost.Name)
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return randHost
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}
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// LeastConn is a policy that selects the host with the least connections.
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type LeastConn struct{}
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// Select selects the up host with the least number of connections in the
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// pool. If more than one host has the same least number of connections,
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// one of the hosts is chosen at random.
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func (r *LeastConn) Select(pool HostPool) *UpstreamHost {
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var bestHost *UpstreamHost
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count := 0
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leastConn := int64(1<<63 - 1)
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for _, host := range pool {
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if host.Down() {
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continue
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}
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hostConns := host.Conns
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if hostConns < leastConn {
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bestHost = host
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leastConn = hostConns
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count = 1
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} else if hostConns == leastConn {
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// randomly select host among hosts with least connections
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count++
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if count == 1 {
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bestHost = host
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} else {
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r := rand.Int() % count
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if r == (count - 1) {
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bestHost = host
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}
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}
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}
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}
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return bestHost
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}
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// RoundRobin is a policy that selects hosts based on round robin ordering.
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type RoundRobin struct {
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Robin uint32
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}
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// Select selects an up host from the pool using a round robin ordering scheme.
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func (r *RoundRobin) Select(pool HostPool) *UpstreamHost {
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poolLen := uint32(len(pool))
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selection := atomic.AddUint32(&r.Robin, 1) % poolLen
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host := pool[selection]
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// if the currently selected host is down, just ffwd to up host
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for i := uint32(1); host.Down() && i < poolLen; i++ {
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host = pool[(selection+i)%poolLen]
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}
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return host
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}
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