For more detailed information about job options and behavior, see the [Docker CLI documentation](/reference/cli/docker/service/create.md#running-as-a-job)

### `placement`

`placement` specifies constraints and preferences for the platform to select a physical node to run service containers.

#### `constraints`

`constraints` defines a required property the platform's node must fulfill to run the service container. For a further example, see the [CLI reference docs](/reference/cli/docker/service/create.md#constraint).

```yml
deploy:
  placement:
    constraints:
      - disktype=ssd
```

#### `preferences`

`preferences` defines a strategy (currently `spread` is the only supported strategy) to spread tasks evenly 
over the values of the datacenter node label. For a further example, see the [CLI reference docs](/reference/cli/docker/service/create.md#placement-pref)

```yml
deploy:
  placement:
    preferences:
      - spread: node.labels.zone
```

### `replicas`

If the service is `replicated` (which is the default), `replicas` specifies the number of containers that should be
running at any given time.

```yml
services:
  frontend:
    image: example/webapp
    deploy:
      mode: replicated
      replicas: 6
```

### `resources`

`resources` configures physical resource constraints for container to run on platform. Those constraints can be configured
as:

- `limits`: The platform must prevent the container to allocate more.
- `reservations`: The platform must guarantee the container can allocate at least the configured amount.

```yml
services:
  frontend:
    image: example/webapp
    deploy:
      resources:
        limits:
          cpus: '0.50'
          memory: 50M
          pids: 1
        reservations:
          cpus: '0.25'
          memory: 20M
```

#### `cpus`

`cpus` configures a limit or reservation for how much of the available CPU resources, as number of cores, a container can use.

#### `memory`

`memory` configures a limit or reservation on the amount of memory a container can allocate, set as a string expressing a [byte value](extension.md#specifying-byte-values).

#### `pids`

`pids` tunes a container’s PIDs limit, set as an integer.

#### `devices`

`devices` configures reservations of the devices a container can use. It contains a list of reservations, each set as an object with the following parameters: `capabilities`, `driver`, `count`, `device_ids` and `options`.

Devices are reserved using a list of capabilities, making `capabilities` the only required field. A device must satisfy all the requested capabilities for a successful reservation.

##### `capabilities`

`capabilities` are set as a list of strings, expressing both generic and driver specific capabilities.
The following generic capabilities are recognized today:

- `gpu`: Graphics accelerator
- `tpu`: AI accelerator

To avoid name clashes, driver specific capabilities must be prefixed with the driver name.
For example, reserving an NVIDIA CUDA-enabled accelerator might look like this:

```yml
deploy:
  resources:
    reservations:
      devices:
        - capabilities: ["nvidia-compute"]
```

##### `driver`

A different driver for the reserved device(s) can be requested using `driver` field. The value is specified as a string.

```yml
deploy:
  resources:
    reservations:
      devices:
        - capabilities: ["nvidia-compute"]
          driver: nvidia
```

##### `count`

If `count` is set to `all` or not specified, Compose reserves all devices that satisfy the requested capabilities. Otherwise, Compose reserves at least the number of devices specified. The value is specified as an integer.

```yml
deploy:
  resources:
    reservations:
      devices:
        - capabilities: ["tpu"]
          count: 2
```

`count` and `device_ids` fields are exclusive. Compose returns an error if both are specified.

##### `device_ids`

If `device_ids` is set, Compose reserves devices with the specified IDs provided they satisfy the requested capabilities. The value is specified as a list of strings.