reverse_proxy: Allow dynamic backends (closes #990 and #1539)

This PR enables the use of placeholders in an upstream's Dial address.

A Dial address must represent precisely one socket after replacements.

See also #998 and #1639.

listeners.go

@@ -286,9 +286,10 @@ func JoinNetworkAddress(network, host, port string) string {
 	if network != "" {
 		a = network + "/"
 	}
-	a += host
-	if port != "" {
-		a += ":" + port
+	if host != "" && port == "" {
+		a += host
+	} else if port != "" {
+		a += net.JoinHostPort(host, port)
 	}
 	return a
 }

listeners_test.go

@@ -138,6 +138,10 @@ func TestJoinNetworkAddress(t *testing.T) {
 			network: "unix", host: "/foo/bar", port: "",
 			expect: "unix//foo/bar",
 		},
+		{
+			network: "", host: "::1", port: "1234",
+			expect: "[::1]:1234",
+		},
 	} {
 		actual := JoinNetworkAddress(tc.network, tc.host, tc.port)
 		if actual != tc.expect {

modules/caddyhttp/reverseproxy/caddyfile.go

@@ -81,9 +81,7 @@ func parseCaddyfile(h httpcaddyfile.Helper) (caddyhttp.MiddlewareHandler, error)
 func (h *Handler) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {
 	for d.Next() {
 		for _, up := range d.RemainingArgs() {
-			h.Upstreams = append(h.Upstreams, &Upstream{
-				Dial: up,
-			})
+			h.Upstreams = append(h.Upstreams, &Upstream{Dial: up})
 		}
 
 		for d.NextBlock(0) {
@@ -94,9 +92,7 @@ func (h *Handler) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {
 					return d.ArgErr()
 				}
 				for _, up := range args {
-					h.Upstreams = append(h.Upstreams, &Upstream{
-						Dial: up,
-					})
+					h.Upstreams = append(h.Upstreams, &Upstream{Dial: up})
 				}
 
 			case "lb_policy":
@@ -502,6 +498,7 @@ func (h *HTTPTransport) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {
 				if d.Val() == "off" {
 					var disable bool
 					h.KeepAlive.Enabled = &disable
+					break
 				}
 				dur, err := time.ParseDuration(d.Val())
 				if err != nil {
@@ -521,6 +518,7 @@ func (h *HTTPTransport) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {
 					h.KeepAlive = new(KeepAlive)
 				}
 				h.KeepAlive.MaxIdleConns = num
+				h.KeepAlive.MaxIdleConnsPerHost = num
 
 			default:
 				return d.Errf("unrecognized subdirective %s", d.Val())

modules/caddyhttp/reverseproxy/healthchecks.go

@@ -115,7 +115,7 @@ func (h *Handler) doActiveHealthChecksForAllHosts() {
 				// so use a fake Host value instead; unix sockets are usually local
 				hostAddr = "localhost"
 			}
-			err = h.doActiveHealthCheck(NewDialInfo(network, addrs[0]), hostAddr, host)
+			err = h.doActiveHealthCheck(DialInfo{Network: network, Address: addrs[0]}, hostAddr, host)
 			if err != nil {
 				log.Printf("[ERROR] reverse_proxy: active health check for host %s: %v", networkAddr, err)
 			}
@@ -259,7 +259,7 @@ func (h *Handler) countFailure(upstream *Upstream) {
 	err := upstream.Host.CountFail(1)
 	if err != nil {
 		log.Printf("[ERROR] proxy: upstream %s: counting failure: %v",
-			upstream.dialInfo, err)
+			upstream.Dial, err)
 	}
 
 	// forget it later
@@ -268,7 +268,7 @@ func (h *Handler) countFailure(upstream *Upstream) {
 		err := host.CountFail(-1)
 		if err != nil {
 			log.Printf("[ERROR] proxy: upstream %s: expiring failure: %v",
-				upstream.dialInfo, err)
+				upstream.Dial, err)
 		}
 	}(upstream.Host, failDuration)
 }

modules/caddyhttp/reverseproxy/hosts.go

@@ -72,7 +72,6 @@ type Upstream struct {
 
 	healthCheckPolicy *PassiveHealthChecks
 	cb                CircuitBreaker
-	dialInfo          DialInfo
 }
 
 // Available returns true if the remote host
@@ -149,8 +148,7 @@ func (uh *upstreamHost) CountFail(delta int) error {
 }
 
 // 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.
+// and returns true if the new value is different.
 func (uh *upstreamHost) SetHealthy(healthy bool) (bool, error) {
 	var unhealthy, compare int32 = 1, 0
 	if healthy {
@@ -167,42 +165,56 @@ func (uh *upstreamHost) SetHealthy(healthy bool) (bool, error) {
 // a host that can be represented in a URL, but
 // they certainly have a network name and address).
 type DialInfo struct {
-	// The network to use. This should be one of the
-	// values that is accepted by net.Dial:
+	// Upstream is the Upstream associated with
+	// this DialInfo. It may be nil.
+	Upstream *Upstream
+
+	// The network to use. This should be one of
+	// the values that is accepted by net.Dial:
 	// https://golang.org/pkg/net/#Dial
 	Network string
 
 	// The address to dial. Follows the same
 	// semantics and rules as net.Dial.
 	Address string
 
-	// Host and Port are components of Address,
-	// pre-split for convenience.
+	// Host and Port are components of Address.
 	Host, Port string
 }
 
-// NewDialInfo creates and populates a DialInfo
-// for the given network and address. It splits
-// the address into host and port values if the
-// network type supports them, or uses the whole
-// address as the port if splitting fails.
-func NewDialInfo(network, address string) DialInfo {
-	var addrHost, addrPort string
-	if !strings.Contains(network, "unix") {
-		var err error
-		addrHost, addrPort, err = net.SplitHostPort(address)
-		if err != nil {
-			addrHost = address // assume there was no port
-		}
-	}
-	return DialInfo{network, address, addrHost, addrPort}
-}
-
 // String returns the Caddy network address form
 // by joining the network and address with a
 // forward slash.
 func (di DialInfo) String() string {
-	return di.Network + "/" + di.Address
+	return caddy.JoinNetworkAddress(di.Network, di.Host, di.Port)
+}
+
+// fillDialInfo returns a filled DialInfo for the given upstream, using
+// the given Replacer. Note that the returned value is not a pointer.
+func fillDialInfo(upstream *Upstream, repl caddy.Replacer) (DialInfo, error) {
+	dial := repl.ReplaceAll(upstream.Dial, "")
+	netw, addrs, err := caddy.ParseNetworkAddress(dial)
+	if err != nil {
+		return DialInfo{}, fmt.Errorf("upstream %s: invalid dial address %s: %v", upstream.Dial, dial, err)
+	}
+	if len(addrs) != 1 {
+		return DialInfo{}, fmt.Errorf("upstream %s: dial address must represent precisely one socket: %s represents %d",
+			upstream.Dial, dial, len(addrs))
+	}
+	var dialHost, dialPort string
+	if !strings.Contains(netw, "unix") {
+		dialHost, dialPort, err = net.SplitHostPort(addrs[0])
+		if err != nil {
+			dialHost = addrs[0] // assume there was no port
+		}
+	}
+	return DialInfo{
+		Upstream: upstream,
+		Network:  netw,
+		Address:  addrs[0],
+		Host:     dialHost,
+		Port:     dialPort,
+	}, nil
 }
 
 // DialInfoCtxKey is used to store a DialInfo