package reverseproxy import ( "context" "fmt" weakrand "math/rand" "net" "net/http" "strconv" "sync" "time" "github.com/caddyserver/caddy/v2" "go.uber.org/zap" ) func init() { caddy.RegisterModule(SRVUpstreams{}) caddy.RegisterModule(AUpstreams{}) } // SRVUpstreams provides upstreams from SRV lookups. // The lookup DNS name can be configured either by // its individual parts (that is, specifying the // service, protocol, and name separately) to form // the standard "_service._proto.name" domain, or // the domain can be specified directly in name by // leaving service and proto empty. See RFC 2782. // // Lookups are cached and refreshed at the configured // refresh interval. // // Returned upstreams are sorted by priority and weight. type SRVUpstreams struct { // The service label. Service string `json:"service,omitempty"` // The protocol label; either tcp or udp. Proto string `json:"proto,omitempty"` // The name label; or, if service and proto are // empty, the entire domain name to look up. Name string `json:"name,omitempty"` // The interval at which to refresh the SRV lookup. // Results are cached between lookups. Default: 1m Refresh caddy.Duration `json:"refresh,omitempty"` // Configures the DNS resolver used to resolve the // SRV address to SRV records. Resolver *UpstreamResolver `json:"resolver,omitempty"` // If Resolver is configured, how long to wait before // timing out trying to connect to the DNS server. DialTimeout caddy.Duration `json:"dial_timeout,omitempty"` // If Resolver is configured, how long to wait before // spawning an RFC 6555 Fast Fallback connection. // A negative value disables this. FallbackDelay caddy.Duration `json:"dial_fallback_delay,omitempty"` resolver *net.Resolver logger *zap.Logger } // CaddyModule returns the Caddy module information. func (SRVUpstreams) CaddyModule() caddy.ModuleInfo { return caddy.ModuleInfo{ ID: "http.reverse_proxy.upstreams.srv", New: func() caddy.Module { return new(SRVUpstreams) }, } } func (su *SRVUpstreams) Provision(ctx caddy.Context) error { su.logger = ctx.Logger(su) if su.Refresh == 0 { su.Refresh = caddy.Duration(time.Minute) } if su.Resolver != nil { err := su.Resolver.ParseAddresses() if err != nil { return err } d := &net.Dialer{ Timeout: time.Duration(su.DialTimeout), FallbackDelay: time.Duration(su.FallbackDelay), } su.resolver = &net.Resolver{ PreferGo: true, Dial: func(ctx context.Context, _, _ string) (net.Conn, error) { //nolint:gosec addr := su.Resolver.netAddrs[weakrand.Intn(len(su.Resolver.netAddrs))] return d.DialContext(ctx, addr.Network, addr.JoinHostPort(0)) }, } } if su.resolver == nil { su.resolver = net.DefaultResolver } return nil } func (su SRVUpstreams) GetUpstreams(r *http.Request) ([]*Upstream, error) { suAddr, service, proto, name := su.expandedAddr(r) // first, use a cheap read-lock to return a cached result quickly srvsMu.RLock() cached := srvs[suAddr] srvsMu.RUnlock() if cached.isFresh() { return cached.upstreams, nil } // otherwise, obtain a write-lock to update the cached value srvsMu.Lock() defer srvsMu.Unlock() // check to see if it's still stale, since we're now in a different // lock from when we first checked freshness; another goroutine might // have refreshed it in the meantime before we re-obtained our lock cached = srvs[suAddr] if cached.isFresh() { return cached.upstreams, nil } su.logger.Debug("refreshing SRV upstreams", zap.String("service", service), zap.String("proto", proto), zap.String("name", name)) _, records, err := su.resolver.LookupSRV(r.Context(), service, proto, name) if err != nil { // From LookupSRV docs: "If the response contains invalid names, those records are filtered // out and an error will be returned alongside the the remaining results, if any." Thus, we // only return an error if no records were also returned. if len(records) == 0 { return nil, err } su.logger.Warn("SRV records filtered", zap.Error(err)) } upstreams := make([]*Upstream, len(records)) for i, rec := range records { su.logger.Debug("discovered SRV record", zap.String("target", rec.Target), zap.Uint16("port", rec.Port), zap.Uint16("priority", rec.Priority), zap.Uint16("weight", rec.Weight)) addr := net.JoinHostPort(rec.Target, strconv.Itoa(int(rec.Port))) upstreams[i] = &Upstream{Dial: addr} } // before adding a new one to the cache (as opposed to replacing stale one), make room if cache is full if cached.freshness.IsZero() && len(srvs) >= 100 { for randomKey := range srvs { delete(srvs, randomKey) break } } srvs[suAddr] = srvLookup{ srvUpstreams: su, freshness: time.Now(), upstreams: upstreams, } return upstreams, nil } func (su SRVUpstreams) String() string { if su.Service == "" && su.Proto == "" { return su.Name } return su.formattedAddr(su.Service, su.Proto, su.Name) } // expandedAddr expands placeholders in the configured SRV domain labels. // The return values are: addr, the RFC 2782 representation of the SRV domain; // service, the service; proto, the protocol; and name, the name. // If su.Service and su.Proto are empty, name will be returned as addr instead. func (su SRVUpstreams) expandedAddr(r *http.Request) (addr, service, proto, name string) { repl := r.Context().Value(caddy.ReplacerCtxKey).(*caddy.Replacer) name = repl.ReplaceAll(su.Name, "") if su.Service == "" && su.Proto == "" { addr = name return } service = repl.ReplaceAll(su.Service, "") proto = repl.ReplaceAll(su.Proto, "") addr = su.formattedAddr(service, proto, name) return } // formattedAddr the RFC 2782 representation of the SRV domain, in // the form "_service._proto.name". func (SRVUpstreams) formattedAddr(service, proto, name string) string { return fmt.Sprintf("_%s._%s.%s", service, proto, name) } type srvLookup struct { srvUpstreams SRVUpstreams freshness time.Time upstreams []*Upstream } func (sl srvLookup) isFresh() bool { return time.Since(sl.freshness) < time.Duration(sl.srvUpstreams.Refresh) } var ( srvs = make(map[string]srvLookup) srvsMu sync.RWMutex ) // AUpstreams provides upstreams from A/AAAA lookups. // Results are cached and refreshed at the configured // refresh interval. type AUpstreams struct { // The domain name to look up. Name string `json:"name,omitempty"` // The port to use with the upstreams. Default: 80 Port string `json:"port,omitempty"` // The interval at which to refresh the A lookup. // Results are cached between lookups. Default: 1m Refresh caddy.Duration `json:"refresh,omitempty"` // Configures the DNS resolver used to resolve the // domain name to A records. Resolver *UpstreamResolver `json:"resolver,omitempty"` // If Resolver is configured, how long to wait before // timing out trying to connect to the DNS server. DialTimeout caddy.Duration `json:"dial_timeout,omitempty"` // If Resolver is configured, how long to wait before // spawning an RFC 6555 Fast Fallback connection. // A negative value disables this. FallbackDelay caddy.Duration `json:"dial_fallback_delay,omitempty"` resolver *net.Resolver } // CaddyModule returns the Caddy module information. func (AUpstreams) CaddyModule() caddy.ModuleInfo { return caddy.ModuleInfo{ ID: "http.reverse_proxy.upstreams.a", New: func() caddy.Module { return new(AUpstreams) }, } } func (au *AUpstreams) Provision(_ caddy.Context) error { if au.Refresh == 0 { au.Refresh = caddy.Duration(time.Minute) } if au.Port == "" { au.Port = "80" } if au.Resolver != nil { err := au.Resolver.ParseAddresses() if err != nil { return err } d := &net.Dialer{ Timeout: time.Duration(au.DialTimeout), FallbackDelay: time.Duration(au.FallbackDelay), } au.resolver = &net.Resolver{ PreferGo: true, Dial: func(ctx context.Context, _, _ string) (net.Conn, error) { //nolint:gosec addr := au.Resolver.netAddrs[weakrand.Intn(len(au.Resolver.netAddrs))] return d.DialContext(ctx, addr.Network, addr.JoinHostPort(0)) }, } } if au.resolver == nil { au.resolver = net.DefaultResolver } return nil } func (au AUpstreams) GetUpstreams(r *http.Request) ([]*Upstream, error) { repl := r.Context().Value(caddy.ReplacerCtxKey).(*caddy.Replacer) auStr := repl.ReplaceAll(au.String(), "") // first, use a cheap read-lock to return a cached result quickly aAaaaMu.RLock() cached := aAaaa[auStr] aAaaaMu.RUnlock() if cached.isFresh() { return cached.upstreams, nil } // otherwise, obtain a write-lock to update the cached value aAaaaMu.Lock() defer aAaaaMu.Unlock() // check to see if it's still stale, since we're now in a different // lock from when we first checked freshness; another goroutine might // have refreshed it in the meantime before we re-obtained our lock cached = aAaaa[auStr] if cached.isFresh() { return cached.upstreams, nil } name := repl.ReplaceAll(au.Name, "") port := repl.ReplaceAll(au.Port, "") ips, err := au.resolver.LookupIPAddr(r.Context(), name) if err != nil { return nil, err } upstreams := make([]*Upstream, len(ips)) for i, ip := range ips { upstreams[i] = &Upstream{ Dial: net.JoinHostPort(ip.String(), port), } } // before adding a new one to the cache (as opposed to replacing stale one), make room if cache is full if cached.freshness.IsZero() && len(srvs) >= 100 { for randomKey := range aAaaa { delete(aAaaa, randomKey) break } } aAaaa[auStr] = aLookup{ aUpstreams: au, freshness: time.Now(), upstreams: upstreams, } return upstreams, nil } func (au AUpstreams) String() string { return au.Name } type aLookup struct { aUpstreams AUpstreams freshness time.Time upstreams []*Upstream } func (al aLookup) isFresh() bool { return time.Since(al.freshness) < time.Duration(al.aUpstreams.Refresh) } // UpstreamResolver holds the set of addresses of DNS resolvers of // upstream addresses type UpstreamResolver struct { // The addresses of DNS resolvers to use when looking up the addresses of proxy upstreams. // It accepts [network addresses](/docs/conventions#network-addresses) // with port range of only 1. If the host is an IP address, it will be dialed directly to resolve the upstream server. // If the host is not an IP address, the addresses are resolved using the [name resolution convention](https://golang.org/pkg/net/#hdr-Name_Resolution) of the Go standard library. // If the array contains more than 1 resolver address, one is chosen at random. Addresses []string `json:"addresses,omitempty"` netAddrs []caddy.NetworkAddress } // ParseAddresses parses all the configured network addresses // and ensures they're ready to be used. func (u *UpstreamResolver) ParseAddresses() error { for _, v := range u.Addresses { addr, err := caddy.ParseNetworkAddress(v) if err != nil { return err } if addr.PortRangeSize() != 1 { return fmt.Errorf("resolver address must have exactly one address; cannot call %v", addr) } u.netAddrs = append(u.netAddrs, addr) } return nil } var ( aAaaa = make(map[string]aLookup) aAaaaMu sync.RWMutex ) // Interface guards var ( _ caddy.Provisioner = (*SRVUpstreams)(nil) _ UpstreamSource = (*SRVUpstreams)(nil) _ caddy.Provisioner = (*AUpstreams)(nil) _ UpstreamSource = (*AUpstreams)(nil) )