From 6c38ae7381b3338b173c59706673d11783091dee Mon Sep 17 00:00:00 2001
From: Jesper Brix Rosenkilde <jbr@humppa.dk>
Date: Tue, 15 Apr 2025 16:44:53 +0200
Subject: [PATCH] reverseproxy: Add valid Upstream to DialInfo in active health
 checks (#6949)

Currently if we extract the DialInfo from a Request Context during an active health check, then the Upstream in the DialInfo is nil.

This PR attempts to set the Upstream to a sensible value, based on wether or not the Upstream has been overriden in the active health check's config.
---
 modules/caddyhttp/reverseproxy/healthchecks.go | 18 +++++++++++++++---
 modules/caddyhttp/reverseproxy/hosts.go        |  4 +---
 modules/caddyhttp/reverseproxy/reverseproxy.go |  2 +-
 3 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/modules/caddyhttp/reverseproxy/healthchecks.go b/modules/caddyhttp/reverseproxy/healthchecks.go
index f0ffee5b8..f018f40ca 100644
--- a/modules/caddyhttp/reverseproxy/healthchecks.go
+++ b/modules/caddyhttp/reverseproxy/healthchecks.go
@@ -309,7 +309,9 @@ func (h *Handler) doActiveHealthCheckForAllHosts() {
 				}
 			}()
 
-			networkAddr, err := caddy.NewReplacer().ReplaceOrErr(upstream.Dial, true, true)
+			repl := caddy.NewReplacer()
+
+			networkAddr, err := repl.ReplaceOrErr(upstream.Dial, true, true)
 			if err != nil {
 				if c := h.HealthChecks.Active.logger.Check(zapcore.ErrorLevel, "invalid use of placeholders in dial address for active health checks"); c != nil {
 					c.Write(
@@ -344,14 +346,24 @@ func (h *Handler) doActiveHealthCheckForAllHosts() {
 				return
 			}
 			hostAddr := addr.JoinHostPort(0)
-			dialAddr := hostAddr
 			if addr.IsUnixNetwork() || addr.IsFdNetwork() {
 				// this will be used as the Host portion of a http.Request URL, and
 				// paths to socket files would produce an error when creating URL,
 				// so use a fake Host value instead; unix sockets are usually local
 				hostAddr = "localhost"
 			}
-			err = h.doActiveHealthCheck(DialInfo{Network: addr.Network, Address: dialAddr}, hostAddr, networkAddr, upstream)
+
+			// Fill in the dial info for the upstream
+			// If the upstream is set, use that instead
+			dialInfoUpstream := upstream
+			if h.HealthChecks.Active.Upstream != "" {
+				dialInfoUpstream = &Upstream{
+					Dial: h.HealthChecks.Active.Upstream,
+				}
+			}
+			dialInfo, _ := dialInfoUpstream.fillDialInfo(repl)
+
+			err = h.doActiveHealthCheck(dialInfo, hostAddr, networkAddr, upstream)
 			if err != nil {
 				if c := h.HealthChecks.Active.logger.Check(zapcore.ErrorLevel, "active health check failed"); c != nil {
 					c.Write(
diff --git a/modules/caddyhttp/reverseproxy/hosts.go b/modules/caddyhttp/reverseproxy/hosts.go
index 0a676e431..300003f2b 100644
--- a/modules/caddyhttp/reverseproxy/hosts.go
+++ b/modules/caddyhttp/reverseproxy/hosts.go
@@ -17,7 +17,6 @@ package reverseproxy
 import (
 	"context"
 	"fmt"
-	"net/http"
 	"net/netip"
 	"strconv"
 	"sync/atomic"
@@ -100,8 +99,7 @@ func (u *Upstream) Full() bool {
 
 // fillDialInfo returns a filled DialInfo for upstream u, using the request
 // context. Note that the returned value is not a pointer.
-func (u *Upstream) fillDialInfo(r *http.Request) (DialInfo, error) {
-	repl := r.Context().Value(caddy.ReplacerCtxKey).(*caddy.Replacer)
+func (u *Upstream) fillDialInfo(repl *caddy.Replacer) (DialInfo, error) {
 	var addr caddy.NetworkAddress
 
 	// use provided dial address
diff --git a/modules/caddyhttp/reverseproxy/reverseproxy.go b/modules/caddyhttp/reverseproxy/reverseproxy.go
index 5bdafa070..f07d3daeb 100644
--- a/modules/caddyhttp/reverseproxy/reverseproxy.go
+++ b/modules/caddyhttp/reverseproxy/reverseproxy.go
@@ -532,7 +532,7 @@ func (h *Handler) proxyLoopIteration(r *http.Request, origReq *http.Request, w h
 	// the dial address may vary per-request if placeholders are
 	// used, so perform those replacements here; the resulting
 	// DialInfo struct should have valid network address syntax
-	dialInfo, err := upstream.fillDialInfo(r)
+	dialInfo, err := upstream.fillDialInfo(repl)
 	if err != nil {
 		return true, fmt.Errorf("making dial info: %v", err)
 	}