unable to access helloworld App deployed using DCOS Marathon in Azure

In your example, host port is 0, Azure will listen your service on a random port. You need open the port on NSG and lb.

I suggest you could specify the port, you could check the following example:

{  "id": "/dockercloud-hello-world",  "cmd": null,  "cpus": 0.1,  "mem": 32,  "disk": 0,  "instances": 1,  "acceptedResourceRoles": [    "slave_public"  ],  "container": {    "type": "DOCKER",    "volumes": [],    "docker": {      "image": "dockercloud/hello-world",      "network": "BRIDGE",      "portMappings": [        {          "containerPort": 80,          "hostPort": 80,          "protocol": "tcp",          "labels": {},          "name": "test80"        }      ],      "privileged": false,      "parameters": [],      "forcePullImage": true    }  },  "healthChecks": [    {      "gracePeriodSeconds": 10,      "intervalSeconds": 2,      "timeoutSeconds": 10,      "maxConsecutiveFailures": 10,      "portIndex": 0,      "path": "/",      "protocol": "MESOS_HTTP",      "ignoreHttp1xx": false    }  ],  "requirePorts": true}

Note: You should set acceptedResourceRoles to slave_public. More information about this please check this link.

Along with the above-mentioned JSON I need to use the agent URL to access the application. I was missing on that