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| layout | page_title | sidebar_current | description |
|---|---|---|---|
| docs | Runtime Environment | docs-jobspec-environment | Learn how to configure the Nomad runtime environment. |
Runtime Environment
Some settings you specify in your jobspec are passed to tasks when they start. Also, some settings are dynamically allocated when your job is scheduled. Both types of values are made available to your job through environment variables.
Resources
When you request resources for a job, Nomad creates a resource offer. The final resources for your job are not determined until it is scheduled. Nomad will tell you which resources
CPU and Memory
Nomad will pass CPU and memory to your job as NOMAD_CPU_LIMIT and
NOMAD_MEMORY_LIMIT. Your task should use these values to adapt its behavior to
fit inside the resource allocation that nomad provides. For example, you can use
the memory limit to inform how large your in-process cache should be, or to
decide when to flush buffers to disk.
Both CPU and memory are presented as integers. The unit for CPU limit is 1024 = 1Ghz. The unit for memory is megabytes.
Writing your applications to adjust to these values at runtime provides greater scheduling flexibility since you can adjust the resource allocations in your jobspec without needing to change your code. You can also schedule workloads that use dynamic resource allocations so they can scale down/up as your cluster gets more or less busy.
IPs and Named Ports
Each task will receive port allocations on a single IP address. The IP is made
available through NOMAD_IP.
If you requested reserved ports in your jobspec and your task is successfully scheduled, these ports are available for your use. Ports from reserved_ports in the job spec
are not exposed through the environment. If you requested dynamic ports in your
jobspec these are made known to your application via environment variables
NOMAD_PORT_{LABEL}. For example dynamic_ports = ["http"] becomes
NOMAD_PORT_HTTP.
Some drivers such as Docker and QEMU use port mapping. With port mapping the
application code can run on a fixed port and nomad will automatically map a
random allocated port in the driver. In this case, you should use numeric port
labels to indicate which ports are exposed in your container or VM. For example
with dynamic_ports = ["5000"] Docker will automatically map the allocated host
port to port 5000 in the container.
Even with automatic port mapping, numeric ports are also exported via
environment variables such as NOMAD_PORT_5000 so you can use these with
drivers that do not support port mapping. You may also be able to use named
ports if you want to bind to a dynamic port inside a container or VM.
Please see the relevant driver documentation for exact details.
Meta
The jobspec also allows you to specify a meta block to supply arbitrary
configuration to a task. This allows you to easily provide job-specific
configuration even if you use the same executable unit in multiple jobs. These
key-value pairs are passed through to the job as NOMAD_META_{KEY}={value},
where key is UPPERCASED from the jobspec.
Currently there is no enforcement that the meta values be lowercase, but using multiple keys with the same uppercased representation will lead to undefined behavior.