github.com/dkerwin/nomad@v0.3.3-0.20160525181927-74554135514b/website/source/docs/jobspec/environment.html.md (about)

     1  ---
     2  layout: "docs"
     3  page_title: "Runtime Environment"
     4  sidebar_current: "docs-jobspec-environment"
     5  description: |-
     6    Learn how to configure the Nomad runtime environment.
     7  ---
     8  
     9  # Runtime Environment
    10  
    11  Some settings you specify in your [job specification](/docs/jobspec/) are passed to tasks
    12  when they start. Other settings are dynamically allocated when your job is
    13  scheduled. Both types of values are made available to your job through
    14  environment variables.
    15  
    16  ## Summary
    17  
    18  <table class="table table-bordered table-striped">
    19    <tr>
    20      <th>Variable</th>
    21      <th>Description</th>
    22    </tr>
    23    <tr>
    24      <td>NOMAD_ALLOC_DIR</td>
    25      <td>Path to the shared alloc directory</td>
    26    </tr>
    27    <tr>
    28      <td>NOMAD_TASK_DIR</td>
    29      <td>Path to the local task directory</td>
    30    </tr>
    31    <tr>
    32      <td>NOMAD_MEMORY_LIMIT</td>
    33      <td>The task's memory limit in MB</td>
    34    </tr>
    35    <tr>
    36      <td>NOMAD_CPU_LIMIT</td>
    37      <td>The task's CPU limit in MHz</td>
    38    </tr>
    39    <tr>
    40      <td>NOMAD_ALLOC_ID</td>
    41      <td>The allocation ID of the task</td>
    42    </tr>
    43    <tr>
    44      <td>NOMAD_ALLOC_NAME</td>
    45      <td>The allocation name of the task</td>
    46    </tr>
    47    <tr>
    48      <td>NOMAD_ALLOC_INDEX</td>
    49      <td>The allocation index; useful to distinguish instances of task groups</td>
    50    </tr>
    51    <tr>
    52      <td>NOMAD_TASK_NAME</td>
    53      <td>The task's name</td>
    54    </tr>
    55    <tr>
    56      <td>NOMAD_IP_"label"</td>
    57      <td>The IP of the the port with the given label</td>
    58    </tr>
    59    <tr>
    60      <td>NOMAD_PORT_"label"</td>
    61      <td>The port value with the given label</td>
    62    </tr>
    63    <tr>
    64      <td>NOMAD_ADDR_"label"</td>
    65      <td>The IP:Port pair of the the port with the given label</td>
    66    </tr>
    67    <tr>
    68      <td>NOMAD_HOST_PORT_"label"</td>
    69      <td>The host port for the given label if the port is port mapped</td>
    70    </tr>
    71    <tr>
    72      <td>NOMAD_META_"key"</td>
    73      <td>The metadata of the task</td>
    74    </tr>
    75  </table>
    76  
    77  ## Task Identifiers
    78  
    79  Nomad will pass both the allocation ID and name as well as the task's name.
    80  These are given as `NOMAD_ALLOC_ID`, `NOMAD_ALLOC_NAME`, `NOMAD_ALLOC_INDEX` and
    81  `NOMAD_TASK_NAME`. The allocation ID and index can be useful when the task being
    82  run needs a unique identifier or to know its instance count.
    83  
    84  ## Resources
    85  
    86  When you request resources for a job, Nomad creates a resource offer. The final
    87  resources for your job are not determined until it is scheduled. Nomad will
    88  tell you which resources have been allocated after evaluation and placement.
    89  
    90  ### CPU and Memory
    91  
    92  Nomad will pass CPU and memory limits to your job as `NOMAD_CPU_LIMIT` and
    93  `NOMAD_MEMORY_LIMIT`. Your task should use these values to adapt its behavior to
    94  fit inside the resource allocation that nomad provides. For example, you can use
    95  the memory limit to inform how large your in-process cache should be, or to
    96  decide when to flush buffers to disk.
    97  
    98  Both CPU and memory are presented as integers. The unit for CPU limit is
    99  `1024 = 1Ghz`. The unit for memory is `1 = 1 megabytes`.
   100  
   101  Writing your applications to adjust to these values at runtime provides greater
   102  scheduling flexibility since you can adjust the resource allocations in your
   103  job specification without needing to change your code. You can also schedule workloads
   104  that accept dynamic resource allocations so they can scale down/up as your
   105  cluster gets more or less busy.
   106  
   107  ### Networking
   108  
   109  Nomad assigns IPs and ports to your jobs and exposes them via environment
   110  variables. See the [Networking](/docs/jobspec/networking.html) page for more
   111  details.
   112  
   113  ### Task Directories <a id="task_dir"></a>
   114  
   115  Nomad makes the following two directories available to tasks:
   116  
   117  * `alloc/`: This directory is shared across all tasks in a task group and can be
   118    used to store data that needs to be used by multiple tasks, such as a log
   119    shipper.
   120  * `local/`: This directory is private to each task. It can be used to store
   121    arbitrary data that shouldn't be shared by tasks in the task group.
   122  
   123  Both these directories are persisted until the allocation is removed, which
   124  occurs hours after all the tasks in the task group enter terminal states. This
   125  gives time to view the data produced by tasks.
   126  
   127  Depending on the driver and operating system being targeted, the directories are
   128  made available in various ways. For example, on `docker` the directories are
   129  binded to the container, while on `exec` on Linux the directories are mounted into the
   130  chroot. Regardless of how the directories are made available, the path to the
   131  directories can be read through the following environment variables:
   132  `NOMAD_ALLOC_DIR` and `NOMAD_TASK_DIR`.
   133  
   134  ## Meta
   135  
   136  The job specification also allows you to specify a `meta` block to supply arbitrary
   137  configuration to a task. This allows you to easily provide job-specific
   138  configuration even if you use the same executable unit in multiple jobs. These
   139  key-value pairs are passed through to the job as `NOMAD_META_"key"={value}`,
   140  where `key` is UPPERCASED from the job specification.
   141  
   142  Currently there is no enforcement that the meta values be lowercase, but using
   143  multiple keys with the same uppercased representation will lead to undefined
   144  behavior.