github.com/smintz/nomad@v0.8.3/website/source/docs/runtime/environment.html.md.erb (about)

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