Implementing the blue/green deployment with Marathon-LB

Let's go ahead and start deploying the application to understand how blue/green deployment works, by performing the following steps:

1. We will create a new version of the web application that uses the nginx web server, as well as creating a definition file to deploy the nginx web server on our Mesos cluster using Marathon.

2. We should focus on the following two new labels used for managing the blue/green deployment technique:
   • HAPROXY_DEPLOYMENT_GROUP: This label uniquely identifies a pair of apps belonging to a blue/green deployment, and will be used as the app name in the HAProxy configuration.
   • HAPROXY_DEPLOYMENT_ALT_PORT: An alternate service port is required because Marathon requires service ports to be unique across all apps.
3. Then, we will install Python version 3, as required by zdd.py, Git, and our other dependencies...