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// Copyright 2015 Matthew Holt and The Caddy Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package reverseproxy
import (
"fmt"
"net/url"
"sync/atomic"
"github.com/caddyserver/caddy/v2"
)
// Host represents a remote host which can be proxied to.
// Its methods must be safe for concurrent use.
type Host interface {
// NumRequests returns the numnber of requests
// currently in process with the host.
NumRequests() int
// Fails returns the count of recent failures.
Fails() int
// Unhealthy returns true if the backend is unhealthy.
Unhealthy() bool
// CountRequest counts the given number of requests
// as currently in process with the host. The count
// should not go below 0.
CountRequest(int) error
// CountFail counts the given number of failures
// with the host. The count should not go below 0.
CountFail(int) error
// SetHealthy marks the host as either healthy (true)
// or unhealthy (false). If the given status is the
// same, this should be a no-op. It returns true if
// the given status was different, false otherwise.
SetHealthy(bool) (bool, error)
}
// UpstreamPool is a collection of upstreams.
type UpstreamPool []*Upstream
// Upstream bridges this proxy's configuration to the
// state of the backend host it is correlated with.
type Upstream struct {
Host `json:"-"`
Address string `json:"address,omitempty"`
MaxRequests int `json:"max_requests,omitempty"`
// TODO: This could be really useful, to bind requests
// with certain properties to specific backends
// HeaderAffinity string
// IPAffinity string
healthCheckPolicy *PassiveHealthChecks
hostURL *url.URL
cb CircuitBreaker
}
// Available returns true if the remote host
// is available to receive requests. This is
// the method that should be used by selection
// policies, etc. to determine if a backend
// should be able to be sent a request.
func (u *Upstream) Available() bool {
return u.Healthy() && !u.Full()
}
// Healthy returns true if the remote host
// is currently known to be healthy or "up".
// It consults the circuit breaker, if any.
func (u *Upstream) Healthy() bool {
healthy := !u.Host.Unhealthy()
if healthy && u.healthCheckPolicy != nil {
healthy = u.Host.Fails() < u.healthCheckPolicy.MaxFails
}
if healthy && u.cb != nil {
healthy = u.cb.OK()
}
return healthy
}
// Full returns true if the remote host
// cannot receive more requests at this time.
func (u *Upstream) Full() bool {
return u.MaxRequests > 0 && u.Host.NumRequests() >= u.MaxRequests
}
// URL returns the upstream host's endpoint URL.
func (u *Upstream) URL() *url.URL {
return u.hostURL
}
// upstreamHost is the basic, in-memory representation
// of the state of a remote host. It implements the
// Host interface.
type upstreamHost struct {
numRequests int64 // must be first field to be 64-bit aligned on 32-bit systems (see https://golang.org/pkg/sync/atomic/#pkg-note-BUG)
fails int64
unhealthy int32
}
// NumRequests returns the number of active requests to the upstream.
func (uh *upstreamHost) NumRequests() int {
return int(atomic.LoadInt64(&uh.numRequests))
}
// Fails returns the number of recent failures with the upstream.
func (uh *upstreamHost) Fails() int {
return int(atomic.LoadInt64(&uh.fails))
}
// Unhealthy returns whether the upstream is healthy.
func (uh *upstreamHost) Unhealthy() bool {
return atomic.LoadInt32(&uh.unhealthy) == 1
}
// CountRequest mutates the active request count by
// delta. It returns an error if the adjustment fails.
func (uh *upstreamHost) CountRequest(delta int) error {
result := atomic.AddInt64(&uh.numRequests, int64(delta))
if result < 0 {
return fmt.Errorf("count below 0: %d", result)
}
return nil
}
// CountFail mutates the recent failures count by
// delta. It returns an error if the adjustment fails.
func (uh *upstreamHost) CountFail(delta int) error {
result := atomic.AddInt64(&uh.fails, int64(delta))
if result < 0 {
return fmt.Errorf("count below 0: %d", result)
}
return nil
}
// SetHealthy sets the upstream has healthy or unhealthy
// and returns true if the value was different from before,
// or an error if the adjustment failed.
func (uh *upstreamHost) SetHealthy(healthy bool) (bool, error) {
var unhealthy, compare int32 = 1, 0
if healthy {
unhealthy, compare = 0, 1
}
swapped := atomic.CompareAndSwapInt32(&uh.unhealthy, compare, unhealthy)
return swapped, nil
}
// hosts is the global repository for hosts that are
// currently in use by active configuration(s). This
// allows the state of remote hosts to be preserved
// through config reloads.
var hosts = caddy.NewUsagePool()
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