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// Package proxy is middleware that proxies requests.
package proxy
import (
"errors"
"sync/atomic"
"time"
"github.com/miekg/coredns/middleware"
"github.com/miekg/dns"
"golang.org/x/net/context"
)
var errUnreachable = errors.New("unreachable backend")
// Proxy represents a middleware instance that can proxy requests to another DNS server.
type Proxy struct {
Next middleware.Handler
Client *client
Upstreams []Upstream
}
// Upstream manages a pool of proxy upstream hosts. Select should return a
// suitable upstream host, or nil if no such hosts are available.
type Upstream interface {
// The domain name this upstream host should be routed on.
From() string
// Selects an upstream host to be routed to.
Select() *UpstreamHost
// Checks if subpdomain is not an ignored.
IsAllowedPath(string) bool
// Options returns the options set for this upstream
Options() Options
}
// UpstreamHostDownFunc can be used to customize how Down behaves.
type UpstreamHostDownFunc func(*UpstreamHost) bool
// UpstreamHost represents a single proxy upstream
type UpstreamHost struct {
Conns int64 // must be first field to be 64-bit aligned on 32-bit systems
Name string // IP address (and port) of this upstream host
Fails int32
FailTimeout time.Duration
Unhealthy bool
CheckDown UpstreamHostDownFunc
WithoutPathPrefix string
}
// Down checks whether the upstream host is down or not.
// Down will try to use uh.CheckDown first, and will fall
// back to some default criteria if necessary.
func (uh *UpstreamHost) Down() bool {
if uh.CheckDown == nil {
// Default settings
fails := atomic.LoadInt32(&uh.Fails)
return uh.Unhealthy || fails > 0
}
return uh.CheckDown(uh)
}
// tryDuration is how long to try upstream hosts; failures result in
// immediate retries until this duration ends or we get a nil host.
var tryDuration = 60 * time.Second
// ServeDNS satisfies the middleware.Handler interface.
func (p Proxy) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
for _, upstream := range p.Upstreams {
start := time.Now()
// Since Select() should give us "up" hosts, keep retrying
// hosts until timeout (or until we get a nil host).
for time.Now().Sub(start) < tryDuration {
host := upstream.Select()
if host == nil {
RequestDuration.WithLabelValues(upstream.From()).Observe(float64(time.Since(start) / time.Millisecond))
return dns.RcodeServerFailure, errUnreachable
}
atomic.AddInt64(&host.Conns, 1)
reply, backendErr := p.Client.ServeDNS(w, r, host)
atomic.AddInt64(&host.Conns, -1)
if backendErr == nil {
w.WriteMsg(reply)
RequestDuration.WithLabelValues(upstream.From()).Observe(float64(time.Since(start) / time.Millisecond))
return 0, nil
}
timeout := host.FailTimeout
if timeout == 0 {
timeout = 10 * time.Second
}
atomic.AddInt32(&host.Fails, 1)
go func(host *UpstreamHost, timeout time.Duration) {
time.Sleep(timeout)
atomic.AddInt32(&host.Fails, -1)
}(host, timeout)
}
RequestDuration.WithLabelValues(upstream.From()).Observe(float64(time.Since(start) / time.Millisecond))
return dns.RcodeServerFailure, errUnreachable
}
return middleware.NextOrFailure(p.Name(), p.Next, ctx, w, r)
}
// Name implements the Handler interface.
func (p Proxy) Name() string { return "proxy" }
// defaultTimeout is the default networking timeout for DNS requests.
const defaultTimeout = 5 * time.Second
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