github.com/iqoqo/nomad@v0.11.3-0.20200911112621-d7021c74d101/website/pages/docs/runtime/environment.mdx (about)

     1  ---
     2  layout: docs
     3  page_title: Environment - Runtime
     4  sidebar_title: Runtime Environment
     5  description: Learn how to configure the Nomad runtime environment.
     6  ---
     7  
     8  # Runtime Environment
     9  
    10  Some settings you specify in your [job specification][jobspec] are passed
    11  to tasks when they start. Other settings are dynamically allocated when your job
    12  is scheduled. Both types of values are made available to your job through
    13  environment variables.
    14  
    15  ## Summary
    16  
    17  @include 'envvars.mdx'
    18  
    19  ~> Port labels and task names will have any non-alphanumeric or underscore
    20  characters in their names replaced by underscores `_` when they're used in
    21  environment variable names such as `NOMAD_ADDR_<task>_<label>`.
    22  
    23  ## Task Identifiers
    24  
    25  Nomad will pass both the allocation ID and name as well as the task, group and
    26  job's names. These are given as `NOMAD_ALLOC_ID`, `NOMAD_ALLOC_NAME`,
    27  `NOMAD_ALLOC_INDEX`, `NOMAD_JOB_NAME`, `NOMAD_GROUP_NAME` and `NOMAD_TASK_NAME`.
    28  The allocation ID and index can be useful when the task being run needs a unique
    29  identifier or to know its instance count.
    30  
    31  ## Resources
    32  
    33  When you request resources for a job, Nomad creates a resource offer. The final
    34  resources for your job are not determined until it is scheduled. Nomad will
    35  tell you which resources have been allocated after evaluation and placement.
    36  
    37  ### CPU and Memory
    38  
    39  Nomad will pass CPU and memory limits to your job as `NOMAD_CPU_LIMIT` and
    40  `NOMAD_MEMORY_LIMIT`. Your task should use these values to adapt its behavior to
    41  fit inside the resource allocation that nomad provides. For example, you can use
    42  the memory limit to inform how large your in-process cache should be, or to
    43  decide when to flush buffers to disk.
    44  
    45  Both CPU and memory are presented as integers. The unit for CPU limit is
    46  `1024 = 1GHz`. The unit for memory is `1 = 1 megabyte`.
    47  
    48  Writing your applications to adjust to these values at runtime provides greater
    49  scheduling flexibility since you can adjust the resource allocations in your
    50  job specification without needing to change your code. You can also schedule workloads
    51  that accept dynamic resource allocations so they can scale down/up as your
    52  cluster gets more or less busy.
    53  
    54  ### Networking
    55  
    56  Nomad assigns IPs and ports to your jobs and exposes them via environment
    57  variables. See the [Networking](/docs/job-specification/network) page for more
    58  details.
    59  
    60  ### Task Directories
    61  
    62  Nomad makes the following directories available to tasks:
    63  
    64  - `alloc/`: This directory is shared across all tasks in a task group and can be
    65    used to store data that needs to be used by multiple tasks, such as a log
    66    shipper.
    67  - `local/`: This directory is private to each task. It can be used to store
    68    arbitrary data that should not be shared by tasks in the task group.
    69  - `secrets/`: This directory is private to each task, not accessible via the
    70    `nomad alloc fs` command or filesystem APIs and where possible backed by an
    71    in-memory filesystem. It can be used to store secret data that should not be
    72    visible outside the task.
    73  
    74  These directories are persisted until the allocation is removed, which occurs
    75  hours after all the tasks in the task group enter terminal states. This gives
    76  time to view the data produced by tasks.
    77  
    78  Depending on the driver and operating system being targeted, the directories are
    79  made available in various ways. For example, on `docker` the directories are
    80  bound to the container, while on `exec` on Linux the directories are mounted into the
    81  chroot. Regardless of how the directories are made available, the path to the
    82  directories can be read through the `NOMAD_ALLOC_DIR`, `NOMAD_TASK_DIR`, and
    83  `NOMAD_SECRETS_DIR` environment variables.
    84  
    85  ## Meta
    86  
    87  The job specification also allows you to specify a `meta` block to supply arbitrary
    88  configuration to a task. This allows you to easily provide job-specific
    89  configuration even if you use the same executable unit in multiple jobs. These
    90  key-value pairs are passed through to the job as `NOMAD_META_<key>=<value>`
    91  environment variables. Prior to Nomad 0.5.5 the key was uppercased and since
    92  then both the original case and an uppercased version are injected. The
    93  uppercased version will be deprecated in a future release.
    94  
    95  Currently there is no enforcement that the meta keys be lowercase, but using
    96  multiple keys with the same uppercased representation will lead to undefined
    97  behavior.
    98  
    99  [jobspec]: /docs/job-specification 'Nomad Job Specification'
   100  [vault]: /docs/vault-integration 'Nomad Vault Integration'