network Stanza

The network stanza specifies the networking requirements for the task, including the minimum bandwidth and port allocations. 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 tasks with network configuration when they start up.

Nomad 0.10 enables support for the network stanza at the task group level. When the network stanza is defined at the group level with bridge as the networking mode, all tasks in the task group share the same network namespace. This is a prerequisite for Consul Connect. Tasks running within a network namespace are not visible to applications outside the namespace on the same host. This allows Connect enabled applications to bind only to localhost within the shared network stack, and use the proxy for ingress and egress traffic.

Note that this document 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.

job "docs" {
  group "example" {
    task "server" {
      resources {
        network {
          mbits = 200
          port "http" {}
          port "https" {}
          port "lb" {
            static = 8889
          }
        }
      }
    }
  }
}

network Parameters

• mbits (int: 10) - Specifies the bandwidth required in MBits.

• port (Port: nil) - Specifies a TCP/UDP port allocation and can be used to specify both dynamic ports and reserved ports.

• mode (string: "host") - Mode of the network. The following modes are available:

  • none - Task group will have an isolated network without any network interfaces.
  • bridge - Task group will have an isolated network namespace with an interface that is bridged with the host. Note that bridge networking is only currently supported for the docker, exec, raw_exec, and java task drivers.
  • host - Each task will join the host network namespace and a shared network namespace is not created. This matches the current behavior in Nomad 0.9.

port Parameters

• static (int: nil) - Specifies the static TCP/UDP port to allocate. If omitted, a dynamic port is chosen. We do not recommend using static ports, except for system or specialized jobs like load balancers.
• to (string:nil) - Applicable when using "bridge" mode to configure port to map to inside the task's network namespace. -1 sets the mapped port equal to the dynamic port allocated by the scheduler. The NOMAD_PORT_<label> environment variable will contain the to value.

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

port "foo" {}

When the task starts, it will be passed the following environment variables:

• NOMAD_IP_foo - The IP to bind on for the given port label.
• NOMAD_PORT_foo - The port value for the given port label.
• NOMAD_ADDR_foo - A combinedip:port that can be used for convenience.

The label of the port is just text - it has no special meaning to Nomad.

network Examples

The following examples only show the network stanzas. Remember that the network stanza is only valid in the placements listed above.

Bandwidth

This example specifies a resource requirement of 1 Gbit in bandwidth:

network {
  mbits = 1000
}

Dynamic Ports

This example specifies a dynamic port allocation for the port labeled "http". Dynamic ports are allocated in a range from 20000 to 32000.

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 to know which port to bind to at startup.

task "example" {
  resources {
    network {
      port "http" {}
      port "https" {}
    }
  }
}

network {
  port "http" {}
}

Static Ports

This example specifies a static port allocation for the port labeled "lb". Static ports bind your job to a specific port on the host they' are placed on. Since multiple services cannot share a port, the port must be open in order to place your task.

network {
  port "lb" {
    static = 6539
  }
}

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 virtual machine.

task "example" {
  driver = "docker"

  config {
    port_map = {
      http = 8080
    }
  }

  resources {
    network {
      port "http" {}
    }
  }
}

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.

When the task is started, it is passed an additional environment variable named NOMAD_HOST_PORT_http which indicates the host port that the HTTP service is bound to.

Bridge Mode

The following example is a group level network stanza that uses bridge mode and port mapping.

network {
  mode = "bridge"
    port "http" {
      static = 9002
      to     = 9002
    }
}

Limitations

• Only one network stanza can be specified, when it is defined at the task group level.
• Only the NOMAD_PORT_<label> and NOMAD_HOST_PORT_<label> environment variables are set for group network ports.