fix: use per-endpoint hostname for health checks with auto-host-rewrite by albsga4 · Pull Request #8851 · envoyproxy/gateway

albsga4 · 2026-04-24T17:46:22Z

What type of PR is this?

fix: health check Host header for external backends with hostname.type: Backend

What this PR does / why we need it:

When hostname.type: Backend (auto-host-rewrite) is configured on an HTTPRoute, active health checks currently send the route hostname as the Host header instead of the backend endpoint FQDN. This causes health checks to fail for external backends that validate the Host header.

The root cause: SetHTTPHostIfAbsent(r.Hostname) in backendtrafficpolicy.go always sets the health check Host to the route hostname. The per-endpoint hostname fallback in getHealthCheckOverridesHostname (#8452) only triggers when HTTP.Host is empty — which it never is, because SetHTTPHostIfAbsent already filled it.

Fix:

Add HostFrom field (Endpoint | Route) to the ActiveHealthCheck IR struct. When the route has hostname.type: Backend configured and the user didn't explicitly set healthCheck.active.http.hostname:

backendtrafficpolicy.go sets HostFrom = Endpoint on the health check
SetHTTPHostIfAbsent still runs (cluster-level host is set, IR validation passes)
getHealthCheckOverridesHostname checks HostFrom — when Endpoint, it returns the endpoint FQDN as per-endpoint HealthCheckConfig.Hostname
Envoy's per-endpoint hostname overrides the cluster-level host for health checks
If the user explicitly sets http.hostname, it takes precedence (HostFrom is not set)

Tested scenarios:

Config	Cluster-level host	Per-endpoint hc_hostname	Result
FQDN backend + `hostname.type: Backend`	route hostname (fallback)	endpoint FQDN	NEW — per-endpoint wins
FQDN backend, no auto-host-rewrite	route hostname	(none)	Unchanged
FQDN backend + explicit `http.hostname`	user's value	(none)	User's explicit value wins
Static URLRewrite hostname	route hostname	(none)	Unchanged

All scenarios verified on a live cluster with multi-cell FQDN backends.

Changes:

internal/ir/xds.go — HealthCheckHostFrom type + HostFrom field on ActiveHealthCheck + SetActiveHostFrom method
internal/gatewayapi/backendtrafficpolicy.go — set HostFrom = Endpoint when routeHasBackendHostRewrite && !hasExplicitHealthCheckHostname
internal/xds/translator/cluster.go — getHealthCheckOverridesHostname checks HostFrom
New test: backendtrafficpolicy-with-healthcheck-auto-host-rewrite exercising HostFrom with auto-host-rewrite
Includes health check testdata from fix: HealthCheck should respect endpoint hostname #8854
Deepcopy regenerated, release note added

Which issue(s) this PR fixes:

Fixes #8848

Release Notes: Yes

/cc @arkodg @zirain

When hostname.type: Backend (auto-host-rewrite) is configured on an HTTPRoute, health checks now use the backend endpoint FQDN as the Host header instead of the route hostname. Add HostFrom field (Endpoint|Route) to ActiveHealthCheck IR. When the route has auto-host-rewrite, HostFrom is set to Endpoint, and the xDS translator sets per-endpoint HealthCheckConfig.Hostname to override the cluster-level Host header. Also auto-derives DestinationEndpoint.Hostname from FQDN.Hostname when not explicitly set, so the endpoint always has a hostname available. Routes without auto-host-rewrite are unchanged — they continue to use the route hostname for health checks. Fixes envoyproxy#8848 Signed-off-by: asalvador <[email protected]>

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When the user explicitly sets healthCheck.active.http.hostname in the BackendTrafficPolicy, it should take precedence over the per-endpoint FQDN even when hostname.type: Backend is configured. Only set HostFrom=Endpoint when the user didn't provide an explicit hostname. Signed-off-by: asalvador <[email protected]>

Signed-off-by: asalvador <[email protected]>

albsga4 · 2026-04-24T19:17:10Z

@codex review

chatgpt-codex-connector · 2026-04-24T19:23:21Z

Codex Review: Didn't find any major issues. More of your lovely PRs please.

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zirain · 2026-04-25T00:14:05Z

looks good to me, can you include the testdata changes from #8854 and make CI happy?

albsga4 · 2026-04-25T00:24:20Z

Thanks @zirain! Including testdata from #8854 in the next push.

Also found and fixing an issue: the initial commit auto-derived DestinationEndpoint.Hostname from FQDN.Hostname in route.go, which changed IR output for all FQDN backends and broke existing golden tests. Removing that — not needed since users with hostname.type: Backend already set endpoint.hostname explicitly.

Next push will have:

Revert auto-derive in route.go
Testdata from fix: HealthCheck should respect endpoint hostname #8854
New test for HostFrom with auto-host-rewrite
Clean golden files (no modifications to existing ones)

@zirain

…ostFrom test - Remove auto-derive of DestinationEndpoint.Hostname from FQDN in route.go (changed IR output for all FQDN backends unnecessarily) - Include health check testdata from envoyproxy#8854 (by @zirain) - Add backendtrafficpolicy-with-healthcheck-auto-host-rewrite test exercising HostFrom=Endpoint with hostname.type: Backend Signed-off-by: asalvador <[email protected]>

zirain · 2026-04-25T00:32:27Z

+// (auto-host-rewrite) configured, meaning the backend FQDN should be used as the
+// Host header for both requests and health checks.
+func routeHasBackendHostRewrite(r *ir.HTTPRoute) bool {
+	return r.URLRewrite != nil &&


URLRewrite could happend per-route and per-backend, we need to handle both.

Good point. For this PR, routeHasBackendHostRewrite checks route-level URLRewrite since that's where hostname.type: Backend is set — the signal that health checks should use the per-endpoint FQDN.

Per-backend static URLRewrite (urlRewrite.hostname: example.com) sets a fixed Host for forwarding but doesn't change the health check Host, since health checks apply at the cluster level from the BTP.

zirain · 2026-04-25T00:34:29Z

@albsga4 I'm sorry, can you update the testdata from #8854, I add a new test case that host rewrite happen on route rule.

codecov · 2026-04-25T00:44:10Z

Codecov Report

❌ Patch coverage is 90.47619% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 74.41%. Comparing base (cab6837) to head (c5f55db).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/gatewayapi/backendtrafficpolicy.go	85.71%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8851      +/-   ##
==========================================
+ Coverage   74.39%   74.41%   +0.01%     
==========================================
  Files         246      246              
  Lines       39221    39240      +19     
==========================================
+ Hits        29180    29200      +20     
+ Misses       8017     8015       -2     
- Partials     2024     2025       +1

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Signed-off-by: asalvador <[email protected]>

zirain · 2026-04-25T01:53:52Z

+            socketAddress:
+              address: example2.com
+              portValue: 3001
+          hostname: example2.com


Corrent me if I'm wrong, rule-1 has a rule level host rewrite, should adopt endpoint host.

zirain · 2026-04-25T01:55:29Z

+            socketAddress:
+              address: example3.com
+              portValue: 3001
+          healthCheckConfig:


Corrent me if I'm wrong, for rule-0, host rewrite happend on backend level, example3 shouldn't has endpoint level healthCheckConfig.

albsga4 · 2026-04-25T02:08:22Z

@zirain Thanks for the detailed review. To clarify the scope of this PR:

Case	Health check Host	Workaround?
No rewrite	Route hostname	Works as-is
Explicit `http.hostname` set	User's value	User controls it
Static `urlRewrite.hostname: X` (route or backend level)	Route hostname	Set `http.hostname: X` — target is known
`hostname.type: Backend` (auto-host-rewrite)	Route hostname (wrong)	No workaround — each endpoint has a different FQDN

This PR addresses the only case with no workaround: hostname.type: Backend where each endpoint has a different FQDN. A single static http.hostname can't cover multiple endpoints.

For static urlRewrite.hostname: X, the target is a known fixed value — the user can set http.hostname: X to match. Same for per-backend static URLRewrite.

Happy to expand to other rewrite cases in a follow-up if needed, but wanted to keep this PR focused on the gap that has no existing solution.

zirain · 2026-04-25T05:40:56Z

+      - path:
+          value: "/v2"
+      filters:
+      - type: ExtensionRef


I cannot recall, but can we use this filter in BackendRef only?

cc @arkodg

zirain · 2026-04-25T12:25:29Z

@albsga4 I rework #8854 to address all this issue, can you help to review it?

albsga4 requested a review from a team as a code owner April 24, 2026 17:46

albsga4 mentioned this pull request Apr 24, 2026

Health check Host header should use backend endpoint FQDN when auto-host-rewrite is configured #8848

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chatgpt-codex-connector Bot reviewed Apr 24, 2026

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Comment thread internal/xds/translator/cluster.go

albsga4 mentioned this pull request Apr 24, 2026

Health-check host value with external Backend services #7798

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albsga4 added 2 commits April 24, 2026 21:10

docs: add release note for health check hostname fix

490e8bf

Signed-off-by: asalvador <[email protected]>

zirain reviewed Apr 25, 2026

View reviewed changes

albsga4 added 2 commits April 25, 2026 03:06

fix: update testdata from latest envoyproxy#8854 (fixes yamllint)

f4aafad

Signed-off-by: asalvador <[email protected]>

test: improve coverage for HostFrom and hasExplicitHealthCheckHostname

c5f55db

Signed-off-by: asalvador <[email protected]>

zirain reviewed Apr 25, 2026

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albsga4 mentioned this pull request Apr 25, 2026

fix: HealthCheck should respect endpoint hostname #8854

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