Managing applications

A Mesos cluster is managed with the dcos tool and the web interface. Applications in Mesos are handled by the Marathon scheduler and are defined in JSON format.

Running a simple application

Let's start with a simple container that runs Nginx. Create a file named nginx.json that contains the following definition:

{ 
  "id" : "simple-nginx", 
  "instances" : 1, 
  "cpus" : 0.25, 
  "mem" : 64.0, 
  "container" : { 
    "type" : "DOCKER", 
    "docker" : { 
      "image" : "nginx:1.11", 
      "network" : "HOST" 
    } 
  } 
} 

The id tag is the name of the service. It is displayed in the service list. The instances tag tells Marathon that only one instance is needed. It can be increased or decreased as needed later.

The cpus and mem tags are hints to Marathon as to what percentage of CPU and the amount of RAM is needed. They do not actually set resource limits in Docker. However, Marathon may kill tasks that...