Add following labels to `frontend` service

```yaml
  - "traefik.http.routers.custom-domain.rule=Host(`custom.localhost`)"
  # Comment the entrypoints label if traefik already has default entrypoint set
  - "traefik.http.routers.custom-domain.entrypoints=web"
  - "traefik.http.middlewares.custom-domain.headers.customrequestheaders.Host=mysite.localhost"
  - "traefik.http.routers.custom-domain.middlewares=custom-domain"
  # Add following header only if TLS is needed in case of live server, use one of below
  - "traefik.http.routers.custom-domain.tls.certresolver=myresolver" # For Single Bench
  - "traefik.http.routers.custom-domain.tls.certresolver=le" # For Docker Swarm
```

Example:

```yaml
frontend:
  ...
  labels:
    ...
    - "traefik.http.routers.custom-domain.rule=Host(`custom.localhost`)"
    - "traefik.http.routers.custom-domain.entrypoints=web"
    - "traefik.http.middlewares.custom-domain.headers.customrequestheaders.Host=mysite.localhost"
    - "traefik.http.routers.custom-domain.middlewares=custom-domain"
    # Add following header only if TLS is needed in case of live server
    - "traefik.http.routers.custom-domain.tls.certresolver=myresolver"
    ...
```

This will add `custom.localhost` as custom domain for `mysite.localhost`