diff options
Diffstat (limited to 'modules/caddyhttp/reverseproxy/upstream.go')
| -rwxr-xr-x | modules/caddyhttp/reverseproxy/upstream.go | 413 |
1 files changed, 413 insertions, 0 deletions
diff --git a/modules/caddyhttp/reverseproxy/upstream.go b/modules/caddyhttp/reverseproxy/upstream.go new file mode 100755 index 0000000..b521d46 --- /dev/null +++ b/modules/caddyhttp/reverseproxy/upstream.go @@ -0,0 +1,413 @@ +// Package reverseproxy implements a load-balanced reverse proxy. +package reverseproxy + +import ( + "context" + "encoding/json" + "fmt" + "math/rand" + "net" + "net/http" + "net/url" + "strings" + "sync" + "sync/atomic" + "time" + + "bitbucket.org/lightcodelabs/caddy2" +) + +// State represents the global state of a loadbalancer. It is used to store +// references to health checkers. +type State struct { + HealthCheckers []*HealthChecker +} + +// CircuitBreaker defines the functionality of a circuit breaker module. +type CircuitBreaker interface { + Ok() bool + RecordMetric(statusCode int, latency time.Duration) +} + +type noopCircuitBreaker struct{} + +func (ncb noopCircuitBreaker) RecordMetric(statusCode int, latency time.Duration) {} +func (ncb noopCircuitBreaker) Ok() bool { + return true +} + +const ( + // TypeBalanceRoundRobin represents the value to use for configuring a load balanced reverse proxy to use round robin load balancing. + TypeBalanceRoundRobin = iota + + // TypeBalanceRandom represents the value to use for configuring a load balanced reverse proxy to use random load balancing. + TypeBalanceRandom + + // msgNoHealthyUpstreams is returned if there are no upstreams that are healthy to proxy a request to + msgNoHealthyUpstreams = "No healthy upstreams." + + // by default perform health checks every 30 seconds + defaultHealthCheckDur = time.Second * 30 + + // used when an upstream is unhealthy, health checks can be configured to perform at a faster rate + defaultFastHealthCheckDur = time.Second * 1 +) + +var ( + // defaultTransport is the default transport to use for the reverse proxy. + defaultTransport = &http.Transport{ + Dial: (&net.Dialer{ + Timeout: 5 * time.Second, + }).Dial, + TLSHandshakeTimeout: 5 * time.Second, + } + + // defaultHTTPClient is the default http client to use for the healthchecker. + defaultHTTPClient = &http.Client{ + Timeout: time.Second * 10, + Transport: defaultTransport, + } + + // typeMap maps caddy load balance configuration to the internal representation of the loadbalance algorithm type. + typeMap = map[string]int{ + "round_robin": TypeBalanceRoundRobin, + "random": TypeBalanceRandom, + } +) + +// NewLoadBalancedReverseProxy returns a collection of Upstreams that are to be loadbalanced. +func NewLoadBalancedReverseProxy(lb *LoadBalanced, state *State) error { + // set defaults + if lb.NoHealthyUpstreamsMessage == "" { + lb.NoHealthyUpstreamsMessage = msgNoHealthyUpstreams + } + + if lb.TryInterval == "" { + lb.TryInterval = "20s" + } + + // set request retry interval + ti, err := time.ParseDuration(lb.TryInterval) + if err != nil { + return fmt.Errorf("NewLoadBalancedReverseProxy: %v", err.Error()) + } + lb.tryInterval = ti + + // set load balance algorithm + t, ok := typeMap[lb.LoadBalanceType] + if !ok { + t = TypeBalanceRandom + } + lb.loadBalanceType = t + + // setup each upstream + var us []*upstream + for _, uc := range lb.Upstreams { + // pass the upstream decr and incr methods to keep track of unhealthy nodes + nu, err := newUpstream(uc, lb.decrUnhealthy, lb.incrUnhealthy) + if err != nil { + return err + } + + // setup any configured circuit breakers + var cbModule = "http.responders.reverse_proxy.circuit_breaker" + var cb CircuitBreaker + + if uc.CircuitBreaker != nil { + if _, err := caddy2.GetModule(cbModule); err == nil { + val, err := caddy2.LoadModule(cbModule, uc.CircuitBreaker) + if err == nil { + cbv, ok := val.(CircuitBreaker) + if ok { + cb = cbv + } else { + fmt.Printf("\nerr: %v; cannot load circuit_breaker, using noop", err.Error()) + cb = noopCircuitBreaker{} + } + } else { + fmt.Printf("\nerr: %v; cannot load circuit_breaker, using noop", err.Error()) + cb = noopCircuitBreaker{} + } + } else { + fmt.Println("circuit_breaker module not loaded, using noop") + cb = noopCircuitBreaker{} + } + } else { + cb = noopCircuitBreaker{} + } + nu.CB = cb + + // start a healthcheck worker which will periodically check to see if an upstream is healthy + // to proxy requests to. + nu.healthChecker = NewHealthCheckWorker(nu, defaultHealthCheckDur, defaultHTTPClient) + + // TODO :- if path is empty why does this empty the entire Target? + // nu.Target.Path = uc.HealthCheckPath + + go nu.healthChecker.ScheduleChecks(nu.Target.String()) + state.HealthCheckers = append(state.HealthCheckers, nu.healthChecker) + + us = append(us, nu) + } + + lb.upstreams = us + + return nil +} + +// LoadBalanced represents a collection of upstream hosts that are loadbalanced. It +// contains multiple features like health checking and circuit breaking functionality +// for upstreams. +type LoadBalanced struct { + mu sync.Mutex + numUnhealthy int32 + selectedServer int // used during round robin load balancing + loadBalanceType int + tryInterval time.Duration + upstreams []*upstream + + // The following struct fields are set by caddy configuration. + // TryInterval is the max duration for which request retrys will be performed for a request. + TryInterval string `json:"try_interval"` + + // Upstreams are the configs for upstream hosts + Upstreams []*UpstreamConfig `json:"upstreams"` + + // LoadBalanceType is the string representation of what loadbalancing algorithm to use. i.e. "random" or "round_robin". + LoadBalanceType string `json:"load_balance_type"` + + // NoHealthyUpstreamsMessage is returned as a response when there are no healthy upstreams to loadbalance to. + NoHealthyUpstreamsMessage string `json:"no_healthy_upstreams_message"` +} + +// ServeHTTP implements the http.Handler interface to dispatch an http request to the proper +// server. +func (lb *LoadBalanced) ServeHTTP(w http.ResponseWriter, r *http.Request) error { + // ensure requests don't hang if an upstream does not respond or is not eventually healthy + var u *upstream + var done bool + + retryTimer := time.NewTicker(lb.tryInterval) + defer retryTimer.Stop() + + go func() { + select { + case <-retryTimer.C: + done = true + } + }() + + // keep trying to get an available upstream to process the request + for { + switch lb.loadBalanceType { + case TypeBalanceRandom: + u = lb.random() + case TypeBalanceRoundRobin: + u = lb.roundRobin() + } + + // if we can't get an upstream and our retry interval has ended return an error response + if u == nil && done { + w.WriteHeader(http.StatusBadGateway) + fmt.Fprint(w, lb.NoHealthyUpstreamsMessage) + + return fmt.Errorf(msgNoHealthyUpstreams) + } + + // attempt to get an available upstream + if u == nil { + continue + } + + start := time.Now() + + // if we get an error retry until we get a healthy upstream + res, err := u.ReverseProxy.ServeHTTP(w, r) + if err != nil { + if err == context.Canceled { + return nil + } + + continue + } + + // record circuit breaker metrics + go u.CB.RecordMetric(res.StatusCode, time.Now().Sub(start)) + + return nil + } +} + +// incrUnhealthy increments the amount of unhealthy nodes in a loadbalancer. +func (lb *LoadBalanced) incrUnhealthy() { + atomic.AddInt32(&lb.numUnhealthy, 1) +} + +// decrUnhealthy decrements the amount of unhealthy nodes in a loadbalancer. +func (lb *LoadBalanced) decrUnhealthy() { + atomic.AddInt32(&lb.numUnhealthy, -1) +} + +// roundRobin implements a round robin load balancing algorithm to select +// which server to forward requests to. +func (lb *LoadBalanced) roundRobin() *upstream { + if atomic.LoadInt32(&lb.numUnhealthy) == int32(len(lb.upstreams)) { + return nil + } + + selected := lb.upstreams[lb.selectedServer] + + lb.mu.Lock() + lb.selectedServer++ + if lb.selectedServer >= len(lb.upstreams) { + lb.selectedServer = 0 + } + lb.mu.Unlock() + + if selected.IsHealthy() && selected.CB.Ok() { + return selected + } + + return nil +} + +// random implements a random server selector for load balancing. +func (lb *LoadBalanced) random() *upstream { + if atomic.LoadInt32(&lb.numUnhealthy) == int32(len(lb.upstreams)) { + return nil + } + + n := rand.Int() % len(lb.upstreams) + selected := lb.upstreams[n] + + if selected.IsHealthy() && selected.CB.Ok() { + return selected + } + + return nil +} + +// UpstreamConfig represents the config of an upstream. +type UpstreamConfig struct { + // Host is the host name of the upstream server. + Host string `json:"host"` + + // FastHealthCheckDuration is the duration for which a health check is performed when a node is considered unhealthy. + FastHealthCheckDuration string `json:"fast_health_check_duration"` + + CircuitBreaker json.RawMessage `json:"circuit_breaker"` + + // // CircuitBreakerConfig is the config passed to setup a circuit breaker. + // CircuitBreakerConfig *circuitbreaker.Config `json:"circuit_breaker"` + circuitbreaker CircuitBreaker + + // HealthCheckDuration is the default duration for which a health check is performed. + HealthCheckDuration string `json:"health_check_duration"` + + // HealthCheckPath is the path at the upstream host to use for healthchecks. + HealthCheckPath string `json:"health_check_path"` +} + +// upstream represents an upstream host. +type upstream struct { + Healthy int32 // 0 = false, 1 = true + Target *url.URL + ReverseProxy *ReverseProxy + Incr func() + Decr func() + CB CircuitBreaker + healthChecker *HealthChecker + healthCheckDur time.Duration + fastHealthCheckDur time.Duration +} + +// newUpstream returns a new upstream. +func newUpstream(uc *UpstreamConfig, d func(), i func()) (*upstream, error) { + host := strings.TrimSpace(uc.Host) + protoIdx := strings.Index(host, "://") + if protoIdx == -1 || len(host[:protoIdx]) == 0 { + return nil, fmt.Errorf("protocol is required for host") + } + + hostURL, err := url.Parse(host) + if err != nil { + return nil, err + } + + // parse healthcheck durations + hcd, err := time.ParseDuration(uc.HealthCheckDuration) + if err != nil { + hcd = defaultHealthCheckDur + } + + fhcd, err := time.ParseDuration(uc.FastHealthCheckDuration) + if err != nil { + fhcd = defaultFastHealthCheckDur + } + + u := upstream{ + healthCheckDur: hcd, + fastHealthCheckDur: fhcd, + Target: hostURL, + Decr: d, + Incr: i, + Healthy: int32(0), // assume is unhealthy on start + } + + u.ReverseProxy = newReverseProxy(hostURL, u.SetHealthiness) + return &u, nil +} + +// SetHealthiness sets whether an upstream is healthy or not. The health check worker is updated to +// perform checks faster if a node is unhealthy. +func (u *upstream) SetHealthiness(ok bool) { + h := atomic.LoadInt32(&u.Healthy) + var wasHealthy bool + if h == 1 { + wasHealthy = true + } else { + wasHealthy = false + } + + if ok { + u.healthChecker.Ticker = time.NewTicker(u.healthCheckDur) + + if !wasHealthy { + atomic.AddInt32(&u.Healthy, 1) + u.Decr() + } + } else { + u.healthChecker.Ticker = time.NewTicker(u.fastHealthCheckDur) + + if wasHealthy { + atomic.AddInt32(&u.Healthy, -1) + u.Incr() + } + } +} + +// IsHealthy returns whether an Upstream is healthy or not. +func (u *upstream) IsHealthy() bool { + i := atomic.LoadInt32(&u.Healthy) + if i == 1 { + return true + } + + return false +} + +// newReverseProxy returns a new reverse proxy handler. +func newReverseProxy(target *url.URL, setHealthiness func(bool)) *ReverseProxy { + errorHandler := func(w http.ResponseWriter, r *http.Request, err error) { + // we don't need to worry about cancelled contexts since this doesn't necessarilly mean that + // the upstream is unhealthy. + if err != context.Canceled { + setHealthiness(false) + } + } + + rp := NewSingleHostReverseProxy(target) + rp.ErrorHandler = errorHandler + rp.Transport = defaultTransport // use default transport that times out in 5 seconds + return rp +} |