title: Use constraints to run multiple instances of traefik on one machine
body: <p>I'm trying to use docker and traefik as a load-balancer for a simple blue/green deployment setup and I want to be able to have multiple instances of traefik up at the same time. From what I understand I have to set constraints with:
  <code>--providers.docker.constraints=Label(`key`,`value`)</code>
  but I couldn't figure out what label I have to put on my services so traefik doesn't ignore them. The docs were very vague on this and google hasn't been much help either</p>