Support URLRewrite in HTTPRoutes #4418

zac-nixon · 2025-10-28T21:06:29Z

Description

Supports path and host header rewrites using URLRewrite found in HTTPRouteRule. https://gateway-api.sigs.k8s.io/guides/http-redirect-rewrite/#rewrites

I put lots of descriptions in the code. The TL;DR is that we can fully support both path and header based rewrites using the newly launched ALB URLRewrite feature. One piece that still needs figuring out is that ALB has more powerful rewrite capabilities than listed here. Originally, I was going to use the ListenerRuleConfiguration object to specify it. However, to keep this change manageable, I have only implemented the Gateway API spec.

Checklist

Added tests that cover your change (if possible)
Added/modified documentation as required (such as the README.md, or the docs directory)
Manually tested
Made sure the title of the PR is a good description that can go into the release notes

BONUS POINTS checklist: complete for good vibes and maybe prizes?! 🤯

Backfilled missing tests for code in same general area 🎉
Refactored something and made the world a better place 🌟

k8s-ci-robot · 2025-10-28T21:06:45Z

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pkg/gateway/routeutils/route_rule_transform.go

shraddhabang · 2025-10-29T19:05:31Z

pkg/gateway/routeutils/route_rule_transform.go

+	match := *httpMatch.Path.Value
+
+	/*
+		If we're being asked to replace a prefix with "", we still need to keep one '/' to form a valid path.


Great job on explaining this in details.
We should also add good documentation with these samples in our docs for this feature once we implement it with ELB gaps.

shraddhabang · 2025-10-29T19:08:13Z

pkg/gateway/routeutils/route_validator_test.go

+						},
+						Filters: []gwv1.HTTPRouteFilter{
+							{
+								URLRewrite: &gwv1.HTTPURLRewriteFilter{


I would have preferred if the spec added this validations instead of us doing this for our implementation. Any reason that spec is not doing this on their side?

Turns out route validator is not needed -

# httproutes.gateway.networking.k8s.io "http-app-1" was not valid: # * spec.rules[0]: Invalid value: "object": When using URLRewrite filter with path.replacePrefixMatch, exactly one PathPrefix match must be specified

shraddhabang · 2025-10-29T19:09:41Z

Can you also add E2E tests for this?

shuqz · 2025-10-29T20:52:29Z

pkg/gateway/routeutils/route_rule_transform.go

+	case HTTPRouteKind:
+		return buildHTTPRuleTransforms(gwRule.CommonRulePrecedence.Rule.GetRawRouteRule().(*gwv1.HTTPRouteRule), gwRule.HTTPMatch)
+	default:
+		return []elbv2model.Transform{}


for any other cases, do we want to add a v(1) logging or warning saying only httpRoute is supported for transform?

I don't think so. This is already documented within the gateway api

shuqz · 2025-10-29T20:53:55Z

pkg/gateway/routeutils/route_rule_transform.go

+	return transforms
+}
+
+func generateHostHeaderRewriteTransform(hostname gwv1.PreciseHostname) elbv2model.Transform {


maybe rename it to generateHttpHostHeaderRewriteTransform, same for generateURLRewritePathTransform

any explanation here? :)

because it feels like this function is only for HTTPRoute, but it is a nit change

shuqz · 2025-10-29T20:55:31Z

pkg/gateway/routeutils/route_rule_transform.go

+}
+
+func generatePrefixReplacementRegex(httpMatch *gwv1.HTTPRouteMatch, replacement string) (string, string) {
+	match := *httpMatch.Path.Value


i did not see where we are checking nil for httpMatch

it's done in the routeValidator

shuqz · 2025-10-29T21:09:05Z

pkg/gateway/routeutils/route_rule_transform.go

+		input path = '/foo/', prefixRegex = '(^/foo(/)?)', replacement value = '/cat/$2' results in (again) '/cat//'
+
+		Without the capture group, we would have one '/' too few.
+		input path = '/foo/bar', prefixRegex = '(^/foo(/)?)', replacement value = '/cat$2' results in '/catbar'


thanks for all explanation. can you verify if *httpMatch.Path.Value(match) can be something like /foo/ or replacement can be with Trailing Slash? those cases will lead to double slash right?

Yup it can, I actually have an explicit test case for this, name = prefix path rewrite with explicit '/' on suffix. To answer your question, no we won't add a double slash, because we check if the replacement ends with a /, in that case we don't append the optional capture group.

shuqz · 2025-10-29T21:14:46Z

pkg/gateway/routeutils/loader.go


-	// 2. Remove routes that aren't granted attachment by the listener.
+	// 3. Validate route configuration, filter out bad configurations.
+	validatedRoutes, validationErrors := l.routeValidator.filterToValidRoutes(gw, foo)


can you attach a screenshot of this status update in route to show a failed case with correct failed reason?

Turns out route validator is not needed -

# httproutes.gateway.networking.k8s.io "http-app-1" was not valid: # * spec.rules[0]: Invalid value: "object": When using URLRewrite filter with path.replacePrefixMatch, exactly one PathPrefix match must be specified

zac-nixon · 2025-10-30T05:04:01Z

E2E test result -

Ran 2 of 18 Specs in 915.365 seconds
SUCCESS! -- 2 Passed | 0 Failed | 0 Pending | 16 Skipped
PASS

shraddhabang · 2025-10-30T17:45:03Z

test/e2e/gateway/alb_ip_target_test.go

+					},
+				})
+				Expect(err).NotTo(HaveOccurred())
+			})


Can we verify the transform are applied in the response by sending the http request?

We don't do this for other listener rules, I don't see a reason to do it here.

k8s-ci-robot added the cncf-cla: yes Indicates the PR's author has signed the CNCF CLA. label Oct 28, 2025

k8s-ci-robot requested a review from M00nF1sh October 28, 2025 21:06

k8s-ci-robot added the size/XXL Denotes a PR that changes 1000+ lines, ignoring generated files. label Oct 28, 2025

k8s-ci-robot requested a review from wweiwei-li October 28, 2025 21:06

k8s-ci-robot added the approved Indicates a PR has been approved by an approver from all required OWNERS files. label Oct 28, 2025

shraddhabang reviewed Oct 29, 2025

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k8s-ci-robot added size/XL Denotes a PR that changes 500-999 lines, ignoring generated files. and removed size/XXL Denotes a PR that changes 1000+ lines, ignoring generated files. labels Oct 30, 2025

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zac-nixon force-pushed the znixon/gw-api-transforms-ga-version branch from 4439c4a to 3a3e396 Compare October 30, 2025 18:40

k8s-ci-robot added the needs-rebase Indicates a PR cannot be merged because it has merge conflicts with HEAD. label Oct 31, 2025

zac-nixon added 2 commits October 31, 2025 14:19

lrc + transforms

90c3d82

add e2e tests, remove route validator

fb3074e

zac-nixon force-pushed the znixon/gw-api-transforms-ga-version branch from 3a3e396 to fb3074e Compare October 31, 2025 21:23

k8s-ci-robot removed the needs-rebase Indicates a PR cannot be merged because it has merge conflicts with HEAD. label Oct 31, 2025

Support URLRewrite in HTTPRoutes #4418

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Support URLRewrite in HTTPRoutes #4418

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zac-nixon commented Oct 28, 2025

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zac-nixon Oct 30, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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zac-nixon commented Oct 30, 2025

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zac-nixon Oct 30, 2025 •

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