Fix: Traefik v2 to v3 Migration — Labels and Config Changes

Traefik v3 routes stop working silently after upgrading. The core label syntax is unchanged, but Docker provider network handling, some middleware options, and v1-style labels all need updating.

V1 Labels That No Longer Work

These Traefik v1 labels were deprecated in v2 but silently ignored. In v3 they do nothing — and Traefik gives no warning:

traefik.enable=true
traefik.http.routers.myapp.rule=Host(`app.example.com`)
traefik.http.routers.myapp.entrypoints=websecure
traefik.http.routers.myapp.tls.certresolver=letsencrypt
traefik.http.services.myapp.loadbalancer.server.port=3000
traefik.docker.network=traefik-public

Docker Network Fix

Traefik v3's Docker provider requires explicit network attachment. Create a shared external network and attach both Traefik and your services to it:

services:
  traefik:
    image: traefik:v3
    networks:
      - traefik-public
networks:
  traefik-public:
    external: true

services:
  myapp:
    networks:
      - traefik-public
    labels:
      - "traefik.enable=true"
      - "traefik.docker.network=traefik-public"
      - "traefik.http.routers.myapp.rule=Host(`app.example.com`)"
networks:
  traefik-public:
    external: true

# Create the network once:
docker network create traefik-public

Static Config Changes

If you use traefik.yml, remove swarmMode: false from the Docker provider — it moved to a separate Swarm provider and causes a startup error in v3 if left in the Docker block.

Frequently Asked Questions