Bumping traefik to v3 is a breaking change and should be announced

[taoyouh]

Environmental Info:
K3s Version:

k3s version v1.32.5+k3s1 (8e8f2a47)
go version go1.23.8

Node(s) CPU architecture, OS, and Version:

Linux DESKTOP-1OTQT74 5.15.167.4-microsoft-standard-WSL2 #1 SMP Tue Nov 5 00:21:55 UTC 2024 x86_64 x86_64 x86_64 GNU/Linux

Cluster Configuration:

1 server, 0 agents.

Describe the bug:

After upgrading from 1.31.5+k3s1 to 1.32.5+k3s1, some previous traefik IngressRoute no longer work.

As the traefik official migration guide (https://doc.traefik.io/traefik/migration/v2-to-v3/) said, the dynamic configuration will have a breaking change from traefik v2 to v3, unless you set defaultRuleSyntax: v2 in the static configuration. However I don't find any clue that this was done automatically, and k3s didn't notice the required action in release note.

Steps To Reproduce:

• Installed K3s: 1.31.5+k3s1
• Create an IngressRoute with v2 specific matcher syntax and a corresponding backend service:

apiVersion: traefik.io/v1alpha1
kind: IngressRoute
metadata:
  name: ingress
spec:
  routes:
  - kind: Rule
    match: PathPrefix(`/`, `/index.html`)
    services:
    - kind: Service
      name: website
      port: 80
---
apiVersion: v1
kind: Service
metadata:
  name: website
spec:
  selector:
    app.kubernetes.io/name: website
  ports:
  - port: 80
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: website
spec:
  selector:
    matchLabels:
      app.kubernetes.io/name: website
  template:
    metadata:
      labels:
        app.kubernetes.io/name: website
    spec:
      containers:
      - name: website
        image: nginx:latest
        ports:
        - name: web
          containerPort: 80

• Try curl localhost/index.html
• Upgrade to k3s 1.32.5+k3s1
• Try curl localhost/index.html

Expected behavior:

The IngressRoute shall work. curl shall output the default nginx page.

Actual behavior:

After update, curl is showing 404.

Additional context / logs:

It's easy to workaround this issue. Just follow the official migration guide to add a static config to default to syntax v2. This could be done by adding a manifest in k3s: create file /var/lib/rancher/k3s/server/manifests/traefik-config.yaml with content:

apiVersion: helm.cattle.io/v1
kind: HelmChartConfig
metadata:
  name: traefik
  namespace: kube-system
spec:
  valueContent: |-
      core:
        defaultRuleSyntax: v2

I think we need to announce in the release notes.

[taoyouh]

Actually this is not any "discussion". It's a real issue we have. I don't know why we oversee this breaking change we made and turn it into a "discussion". @brandond could you advise why this is a "discussion"?

[brandond]

You're welcome to discuss the change here, but it's not something that is broken, and we're going to undo or otherwise revert it. The docs have been updated to link to the upstream 2-to-3 migration guide: https://docs.k3s.io/networking/networking-services#traefik-ingress-controller

[taoyouh]

Thank you @brandond for updating the doc. I think that's enough.

[teq0]

This is still really unclear. I tried creating the extra manifest (which isn't mentioned in the updated docs) before doing the upgrade but it had no effect. I fixed the problem by manually editing the Traefik Deployment and adding in the additional arg.

I also had to redeploy the redirect middleware, which isn't mentioned in the upgrade docs anywhere.