You can configure the frontend ports used to expose and access the service for Edge-LB load balancing. You can choose to specify the frontend port for each service manually, or have Edge-LB automatically assign a port by setting a configuration option.

Before you begin

You must have:

• Edge-LB installed as described in the Edge-LB installation instructions.
• The core DC/OS command-line interface (CLI) installed and configured to communicate with the DC/OS cluster.
• The edgelb command-line interface (CLI) installed.
• An active and properly-configured DC/OS Enterprise cluster, with at least one DC/OS private agent node to run the load-balanced service and at least one DC/OS public agent node for exposing the load-balanced service.

Configuring dynamic selection of frontend ports

With Edge-LB, you can dynamically assign the port used to access load balancing statistics by modifying the Edge-LB pool configuration file. Using the settings in the pool configuration file, you can control whether Edge-LB should use a predefined port, or automatically assign a port for accessing load balancing statistics.

Create the sample pool configuration file

1. Open a text editor, then copy and paste the following sample nginx-lb.json pool configuration file that automatically sets the frontend port assignment:

   {
   "apiVersion": "V2",
   "name": "nginx-lb",
   "count": 1,
   "haproxy": {
       "stats": {
       "bindPort": 15001
       },
       "frontends": [{
           "name": "nginx-frontend",
           "bindPort": 0,
           "protocol": "HTTP",
           "linkBackend": {
               "defaultBackend": "nginx-backend"
       }
       }],
       "backends": [{
       "name": "nginx-backend",
       "protocol": "HTTP",
       "services": [{
           "marathon": {
           "serviceID": "/nginx"
           },
           "endpoint": {
           "portName": "nginx-80"
           }
       }]
       }]
   }
   }
   

   In this sample configuration file, the haproxy.frontends.bindPort setting is 0. This setting indicates that you want Edge-LB to automatically select the port to use for the frontend endpoint.

2. Deploy the Edge-LB pool:

   dcos edgelb create nginx-lb.json
   

3. Verify that Edge-LB frontend port is chosen dynamically for the pool:

   dcos edgelb endpoints nginx-lb
   

   This command displays endpoint information including the frontend port that was dynamically selected:

   NAME            PORT   INTERNAL IP           
   frontend_port0  1025  10.0.5.119, 10.0.6.5  
   stats_port      9090   10.0.5.119, 10.0.6.5
   

   In this example, the nginx-lb is pool automatically assigned the frontend port 1025.

4. Navigate to the URL to see the frontend for the nginx service routed through the Edge-LB nginx-lb pool configuration using the public IP address of the public agent.

   For example:

   http://<public_agent_public_IP>:1025
   

Changing a previously-configured port

If you manually configured an Edge-LB pool to use a specific frontend port for a service, updating the pool configuration file to use auto-assignment for the frontend port does not update the port used. For example, if you previously configured port 15000 as the frontend port and updated the Edge-LB pool configuration haproxy.frontends.bindPort setting to 0 for dynamic allocation, Edge-LB will continue to use port 15000 as the frontend port.

To use dynamic port selection, delete the previous pool configuration, then create and deploy a new pool configuration file with the haproxy.frontends.bindPort: 0 setting.

Enabling dynamic port allocation for multiple pools

Assigning a frontend port dynamically enables you to deploy more than one pool on an agent node without manually setting different values for each pool.

By leveraging dynamic port allocation, you can:

• Deploy multiple pools on the same agent without worrying about port conflicts.
• Avoid the limitations imposed by using the default stats port 9090 which restricted you to deploying only one Edge-LB pool per agent.
• Eliminate the need to identify and specify manual port assignments for Edge-LB pools running on the same agent.

When a public cloud load balancer like Amazon® Web Services (AWS®) Elastic Load Balancer® (ELB®) is positioned as an access point in front of an Edge-LB pool, the Elastic Load Balancer manages the proxy and load-balancing responsibilities between the client and the Edge-LB pool. In this scenario, assigning the frontend port dynamically enables you to use multiple frontend ports for multiple Edge-LB pools on the same agent, which results in more efficient resource consumption and utilization.