Port forwards fail to bind on macOS when localhost resolves to fe80::1%lo0

[louismrose]

Expected Behavior

Using k8s_resource with a port forward should work on macOS, when localhost resolves to fe80::1%lo0.

Current Behavior

Port forwarding fails in Tilt with the following error:

Reconnecting... Error port-forwarding test-deploy (9090 -> 9090): error forwarding port: fe80::1%lo0 is not a valid IP

I believe this is an issue with Tilt because I can successfully configure a port forward via Kubernetes for the same service:

$ kubectl port-forward test-deploy-56469867cc-v852c 9090:9090
Forwarding from 127.0.0.1:9090 -> 9090
Forwarding from [::1]:9090 -> 9090
Handling connection for 9090

Interestingly if I try to port forward with Kubernetes via an address hardcoded to fe80::1%lo0 then it fails with exactly the same error message seen in Tilt:

$ kubectl port-forward test-deploy-56469867cc-v852c --address fe80::1%lo0 9090:9090
error: fe80::1%lo0 is not a valid IP

I suspect this is due to net.LookupHost including fe80::1%lo0 in the list of addresses via the default Go resolver on macOS:

$ cat localhost.go
package main

import "fmt"
import "net"

func main() {
        addr, _ := net.LookupHost("localhost")
	fmt.Println("Localhost addresses are:", addr)
}

$ go run localhost.go
Localhost addresses are: [::1 127.0.0.1 fe80::1%lo0]

fe80::1%lo0 seems to appear in /etc/hosts by default on some macOS installations. I believe the %lo0 is intended to restrict traffic to a particular network interface via a "zone index". It looks like Kubernetes doesn't support IP addresses with a zone index, so Tilt probably shouldn't pass addresses of this form to Kubernetes when setting up port forwards.

I had a quick look at internal/k8s/portforward.go, and it looks like getListenableAddresses might be the place to update? Let me know if that's the case, and I can attempt a PR to exclude IP addresses with a zone index.

Steps to Reproduce

1. Ensure you're running on a machine (e.g., macOS) where localhost resolves to fe80::1%lo0 (e.g., by using the sample Go code above).
2. Run tilt up for a Tiltfile including a k8s_resource with port_forwards
3. Observe an error message similar to Reconnecting... Error port-forwarding test-deploy (9090 -> 9090): error forwarding port: fe80::1%lo0 is not a valid IP in the logs for that resource.

Context

tilt doctor Output

$ tilt doctor
Tilt: v0.30.12, built 2022-11-16
System: darwin-arm64
---
Docker
- Host: unix:///var/run/docker.sock
- Server Version: 20.10.21
- API Version: 1.41
- Builder: 2
- Compose Version: v2.12.2
---
Kubernetes
- Env: kind
- Context: kind-crs-tilt
- Cluster Name: kind-crs-tilt
- Namespace: default
- Container Runtime: containerd
- Version: v1.23.13
- Cluster Local Registry: &RegistryHosting{Host:localhost:60929,HostFromClusterNetwork:ctlptl-registry:5000,HostFromContainerRuntime:,Help:https:/tilt-dev/ctlptl,SingleName:,}
---
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About Your Use Case

As I haven't yet been able to figure out how to remove ``fe80::1%lo0from the addresses to whichlocalhost` resolves via `net.LookupHost` (removing the entry from `/etc/hosts` doesn't work), I cannot use Tilt port forwards at all.

I can workaround this by using kubectl port-forward manually instead.

[louismrose]

A colleague noted that a better workaround is tilt up --host 127.0.0.1

[nicksieger]

I was about to ask if tilt up --host '[::1]' would also work, it should. Your analysis is spot on, if you don't mind submitting a PR to exclude addresses with zone indexes that would be great!