github.com/huiliang/nomad@v0.2.1-0.20151124023127-7a8b664699ff/website/source/docs/jobspec/networking.html.md (about)

     1  ---
     2  layout: "docs"
     3  page_title: "Nomad Networking"
     4  sidebar_current: "docs-jobspec-networking"
     5  description: |-
     6    Learn how to configure networking and ports for Nomad tasks.
     7  ---
     8  
     9  # Networking
    10  
    11  When scheduling jobs in Nomad they are provisioned across your fleet of
    12  machines along with other jobs and services. Because you don't know in advance
    13  what host your job will be provisioned on, Nomad will provide your task with
    14  network configuration when they start up.
    15  
    16  Note that this document applies only applies to services that want to _listen_
    17  on a port. Batch jobs or services that only make outbound connections do not
    18  need to allocate ports, since they will use any available interface to make an
    19  outbound connection.
    20  
    21  ## IP Address
    22  
    23  Hosts in Nomad may have multiple network interfaces attached to them. This
    24  allows you to have a higher density of services, or bind to interfaces on
    25  different subnets (for example public vs. private subnets).
    26  
    27  Each task will receive port allocations on a single interface. The IP is passed
    28  to your job via the `NOMAD_IP` environment variable.
    29  
    30  ## Ports
    31  
    32  In addition to allocating an interface, Nomad can allocate static or dynamic
    33  ports to your task.
    34  
    35  ### Dynamic Ports
    36  
    37  Dynamic ports are allocated in a range from `20000` to `60000`.
    38  
    39  Most services run in your cluster should use dynamic ports. This means that the
    40  port will be allocated dynamically by the scheduler, and your service will have
    41  to read an environment variable (see below) to know which port to bind to at
    42  startup.
    43  
    44  ```
    45  task "webservice" {
    46      port "http" {}
    47      port "https" {}
    48  }
    49  ```
    50  
    51  ### Static Ports
    52  
    53  Static ports bind your job to a specific port on the host they're placed on.
    54  Since multiple services cannot share a port, the port must be open in order to
    55  place your task.
    56  
    57  ```
    58  task "dnsservice" {
    59      port "dns" {
    60          static = 53
    61      }        
    62  }
    63  ```
    64  
    65  We recommend _only_ using static ports for [system
    66  jobs](/docs/jobspec/schedulers.html) or specialized jobs like load balancers.
    67  
    68  ### Labels and Environment Variables
    69  
    70  The label assigned to the port is used to identify the port in service
    71  discovery, and used for the name of the environment variable that indicates
    72  which port your application should bind to. For example, we've labeled this
    73  port `http`:
    74  
    75  ```
    76  port "http" {}
    77  ```
    78  
    79  When the task is started, it is passed an environment variable named
    80  `NOMAD_PORT_http` which indicates the port.
    81  
    82  ```
    83  NOMAD_PORT_http=53423 ./start-command
    84  ```
    85  
    86  ### Mapped Ports
    87  
    88  Some drivers (such as Docker and QEMU) allow you to map ports. A mapped port
    89  means that your application can listen on a fixed port (it does not need to
    90  read the environment variable) and the dynamic port will be mapped to the port
    91  in your container or VM.
    92  
    93  ```
    94  driver = "docker"
    95  
    96  port "http" {}
    97  
    98  config {
    99      port_map = {
   100          http = 8080
   101      }
   102  }
   103  ```
   104  
   105  The above example is for the Docker driver. The service is listening on port
   106  `8080` inside the container. The driver will automatically map the dynamic port
   107  to this service.
   108  
   109  Please refer to the [Docker](/docs/drivers/docker.html) and [QEMU](/docs/drivers/qemu.html) drivers for additional information.