On this page
AIBrix built every ModelAdapter EndpointSlice with addressType: IPv4, even when the Pods had IPv6 addresses. I fixed it in PR #3136, merged the same day, about twelve hours after I opened it. The family was a constant in the builder.
When it happens
A ModelAdapter is loaded on Pods whose status.podIP is an IPv6 address such as 2001:db8::1. The controller creates a slice for the adapter Service. The slice declares IPv4 but lists IPv6 addresses, so Kubernetes rejects it and the adapter Service has no endpoints.
I did not run this on an IPv6 cluster. My evidence is the code and the unit test below. There was no existing issue for it.
How the slice is built
reconcileEndpointSlice in modeladapter_controller.go fetches the Pods named in status.instances, then looks for the slice. If there is none, it calls buildModelAdapterEndpointSlice and creates the result. If there is one, it only rewrites Endpoints, and addressType cannot change on an existing slice.
The builder in resources.go copied each status.podIP into an endpoint, then set AddressType: discoveryv1.AddressTypeIPv4 (line 58).
Why the gap existed
The constant came with the controller refactor in #135, in September 2024. The builder’s own test used an IPv4 Pod address and did not assert the family.
The fix
The first backing Pod picks the family. With no Pods it stays IPv4. From resources.go, without the k8s.io/utils/net import (netutils) and the unchanged lines between the two hunks:
+ addressType := discoveryv1.AddressTypeIPv4
+ if len(pods) > 0 && netutils.IsIPv6String(pods[0].Status.PodIP) {
+ addressType = discoveryv1.AddressTypeIPv6
+ }
+
addresses := make([]discoveryv1.Endpoint, 0, len(pods))
@@
- AddressType: discoveryv1.AddressTypeIPv4,
+ AddressType: addressType,The PR body lists what this does not cover. Backing Pods of mixed families would still need separate slices. The family is chosen when the slice is created. Dual-stack Pods are still listed by their primary address, status.podIP.
The test
TestBuildModelAdapterEndpointSliceIPv6 in resources_test.go builds a slice from one Pod with 2001:db8::1 and checks the family and the address. The existing IPv4 test now asserts the IPv4 family too.
Before the fix the new test failed: expected IPv6, actual IPv4. After it, it passed. The package run without the envtest suite passes, 25 tests and 39 subtests. The 18 controller specs need envtest binaries I did not have, so they did not run for me. CI on the PR head was green.
What the maintainer did
@varungup90 left a review that called it “Small, correct fix” and then merged the PR. The review reports that restoring the old resources.go with the new tests fails the same way. It also notes that the len(pods) > 0 guard has no test of its own, and calls that optional. I left the PR as it was.
The lesson
- A hardcoded value is a claim about every input. Ask what the callers can send.
- Assert the old default before you add a new case. The IPv4 test now checks the family it used to assume.
- Write down what the change leaves out. A slice keeps its family, so mixed-family Pods need more than this.
If a builder in your own code assumes one kind of input, reply on X.