open-nomad/website/source/docs/jobspec/networking.html.md

layout	page_title	sidebar_current	description
docs	Nomad Networking	docs-jobspec-networking	Learn how to configure networking and ports for Nomad tasks.

Networking

When scheduling jobs in Nomad they are provisioned across your fleet of machines along with other jobs and services. Because you don't know in advance what host your job will be provisioned on, Nomad will provide your task with network configuration when they start up.

Note that this document applies only applies to services that want to listen on a port. Batch jobs or services that only make outbound connections do not need to allocate ports, since they will use any available interface to make an outbound connection.

IP Address

Hosts in Nomad may have multiple network interfaces attached to them. This allows you to have a higher density of services, or bind to interfaces on different subnets (for example public vs. private subnets).

Each task will receive port allocations on a single interface. The IP is passed to your job via the NOMAD_IP environment variable.

Ports

In addition to allocating an interface, Nomad can allocate static or dynamic ports to your task.

Dynamic Ports

Dynamic ports are allocated in a range from 20000 to 60000.

Most services run in your cluster should use dynamic ports. This means that the port will be allocated dynamically by the scheduler, and your service will have to read an environment variable (see below) to know which port to bind to at startup.

task "webservice" {
    port "http" {}
    port "https" {}
}

Static Ports

Static ports bind your job to a specific port on the host they're placed on. Since multiple services cannot share a port, the port must be open in order to place your task.

task "dnsservice" {
    port "dns" {
        static = 53
    }        
}

We recommend only using static ports for system jobs or specialized jobs like load balancers.

Labels and Environment Variables

The label assigned to the port is used to identify the port in service discovery, and used for the name of the environment variable that indicates which port your application should bind to. For example, we've labeled this port http:

port "http" {}

When the task is started, it is passed an environment variable named NOMAD_PORT_http which indicates the port.

NOMAD_PORT_http=53423 ./start-command

Mapped Ports

Some drivers (such as Docker and QEMU) allow you to map ports. A mapped port means that your application can listen on a fixed port (it does not need to read the environment variable) and the dynamic port will be mapped to the port in your container or VM.

driver = "docker"

port "http" {}

config {
    port_map = {
        http = 8080
    }
}

The above example is for the Docker driver. The service is listening on port 8080 inside the container. The driver will automatically map the dynamic port to this service.

Please refer to the Docker and QEMU drivers for additional information.