First, we will talk about the Swarm blue/green deployment, where we will use a load balancer in conjunction with two versions of a Docker service. The load balancers could be external to our cluster or actually running in a container within our cluster. For the sake of our discussion, let's say it's an external application load balancer that's sitting in front of our cluster.
Figure 4 shows how the process works for Swarm:
Figure 4: The Swarm blue/green migration process
Prior to the update, only items in green are present. Traffic is coming to the load balancer and being forwarded over port 8080 to the
