---
layout: docs
page_title: resources block in the job specification
description: |-
  The "resources" block describes the requirements a task needs to execute.
  Resource requirements include memory, cpu, and more.
---

# `resources` block in the job specification

<Placement groups={['job', 'group', 'task', 'resources']} />

The `resources` block describes the requirements a task needs to execute.
Resource requirements include memory, CPU, and more.

```hcl
job "docs" {
  group "example" {
    task "server" {
      resources {
        cpu    = 100
        memory = 256

        device "nvidia/gpu" {
          count = 2
        }
      }
    }
  }
}
```

## Parameters

- `cpu` `(int: 100)` - Specifies the CPU required to run this task in MHz.

- `cores` <code>(`int`: &lt;optional&gt;)</code> - Specifies the number of CPU cores
  to reserve specifically for the task. This may not be used with `cpu`. The behavior
  of setting `cores` is specific to each task driver (e.g. [docker][docker_cpu], [exec][exec_cpu]).

- `memory` `(int: 300)` - Specifies the memory required in MB.

- `memory_max` <code>(`int`: &lt;optional&gt;)</code> - Optionally, specifies the
  maximum memory the task may use, if the client has excess memory capacity, in MB.
  See [Memory Oversubscription](#memory-oversubscription) for more details.

- `numa` <code>([Numa][]: &lt;optional&gt;)</code> - Specifies the
  NUMA scheduling preference for the task. Requires the use of `cores`.

- `device` <code>([Device][]: &lt;optional&gt;)</code> - Specifies the device
  requirements. This may be repeated to request multiple device types.

- `secrets` <code>(`int`: &lt;optional&gt;)</code> - Specifies the size of the
  [`secrets/`][] directory in MB, on platforms where the directory is a
  tmpfs. If set, the scheduler adds the `secrets` value to the `memory` value
  when allocating resources on a client, and this value will be included in the
  allocated resources shown by the `nomad alloc status` and `nomad node status`
  commands. If unset, the client will allocate 1 MB of tmpfs space and it will
  not be counted for scheduling purposes or included in allocated resources. You
  should not set this value if the workload will be placed on a platform where
  tmpfs is unsupported, because it will still be counted for scheduling
  purposes.

## Examples

The following examples only show the `resources` blocks. Remember that the
`resources` block is only valid in the placements listed above.

### Cores

This example specifies that the task requires 2 reserved cores. With this block,
Nomad finds a client with enough spare capacity to reserve 2 cores exclusively
for the task. Unlike the `cpu` field, the task does not share CPU time with any
other tasks managed by Nomad on the client.

```hcl
resources {
  cores = 2
}
```

If `cores` and `cpu` are both defined in the same resource block, validation of
the job fails.

Refer to [How Nomad Uses CPU][concepts-cpu] for more details on Nomad's
reservation of CPU resources.


### Memory

This example specifies the task requires 2 GB of RAM to operate. 2 GB is the
equivalent of 2048 MB:

```hcl
resources {
  memory = 2048
}
```

### Devices

This example shows a device constraints as specified in the [device][] block
which require two nvidia GPUs to be made available:

```hcl
resources {
  device "nvidia/gpu" {
    count = 2
  }
}
```
## Memory oversubscription

Setting task memory limits requires balancing the risk of interrupting tasks
against the risk of wasting resources. If a task memory limit is set too low,
the task may exceed the limit and be interrupted; if the task memory is too
high, the cluster is left underutilized.

To help maximize cluster memory utilization while allowing a safety margin for
unexpected load spikes, Nomad allows job authors to set two separate memory
limits:

* `memory`: the reserve limit to represent the task’s typical memory usage —
  this number is used by the Nomad scheduler to reserve and place the task

* `memory_max`: the maximum memory the task may use, if the client has excess
  available memory, and may be terminated if it exceeds

If a client's memory becomes contended or low, the operating system will
pressure the running tasks to free up memory. If the contention persists, Nomad
may kill oversubscribed tasks and reschedule them to other clients. The exact
mechanism for memory pressure is specific to the task driver, operating system,
and application runtime.

The `memory_max` limit attribute is currently supported by the official
`raw_exec`, `exec2`, `exec`, `docker`, `podman`, and `java` task drivers.  Consult the
documentation of community-supported task drivers for their memory
oversubscription support.

Memory oversubscription is opt-in. Nomad operators can enable [Memory
Oversubscription in the scheduler configuration][api_sched_config]. Enterprise
customers can use [Resource Quotas][quota_spec] to limit the memory
oversubscription and enable or disable memory oversubscription per [node
pool][np_sched_config].

To avoid degrading the cluster experience, we recommend examining and monitoring
resource utilization and considering the following suggestions:

* Set `oom_score_adj` for Linux host services that aren't managed by Nomad, e.g.
  Docker, logging services, and the Nomad agent itself. For Systemd services, you can use the [`OOMScoreAdj` field](https://github.com/hashicorp/nomad/blob/v1.0.0/dist/systemd/nomad.service#L25).

* Monitor hosts for memory utilization and set alerts on Out-Of-Memory errors

* Set the [client `reserved`](/nomad/docs/configuration/client#reserved) with enough
  memory for host services that aren't managed by Nomad as well as a buffer
  for the memory excess. For example, if the client reserved memory is 1GB,
  the allocations on the host may exceed their soft memory limit by almost
  1GB in aggregate before the memory becomes contended and allocations get
  killed.

[api_sched_config]: /nomad/api-docs/operator/scheduler#update-scheduler-configuration
[device]: /nomad/docs/job-specification/device 'Nomad device Job Specification'
[docker_cpu]: /nomad/docs/drivers/docker#cpu
[exec_cpu]: /nomad/docs/drivers/exec#cpu
[np_sched_config]: /nomad/docs/other-specifications/node-pool#memory_oversubscription_enabled
[quota_spec]: /nomad/docs/other-specifications/quota
[numa]: /nomad/docs/job-specification/numa 'Nomad NUMA Job Specification'
[`secrets/`]: /nomad/docs/runtime/environment#secrets
[concepts-cpu]: /nomad/docs/concepts/cpu
