# Job definition examples
<a name="example-job-definitions"></a>

The job definition examples in the following topics illustrate how to use common patterns such as environment variables, parameter substitution, and volume mounts.

**Topics**
+ [Environment variables](example-use-envvars.md)
+ [Parameter substitution](example-use-parameters.md)
+ [Test GPU functionality](example-test-gpu.md)
+ [Multi-node parallel job](example-mnp-job-definition.md)

# Environment variables
<a name="example-use-envvars"></a>

The following example job definition uses environment variables to specify a file type and Amazon S3 URL. This particular example is from the [Creating a Simple "Fetch & Run" AWS Batch Job](https://aws.amazon.com/blogs/compute/creating-a-simple-fetch-and-run-aws-batch-job/) compute blog post. The [https://github.com/awslabs/aws-batch-helpers/blob/master/fetch-and-run/fetch_and_run.sh](https://github.com/awslabs/aws-batch-helpers/blob/master/fetch-and-run/fetch_and_run.sh) script that's described in the blog post uses these environment variables to download the `myjob.sh` script from S3 and declare its file type.

Even though the command and environment variables are hardcoded into the job definition in this example, you can specify command and environment variable overrides to make the job definition more versatile.

```
{
    "jobDefinitionName": "fetch_and_run",
    "type": "container",
    "containerProperties": {
        "image": "123456789012.dkr.ecr.us-east-1.amazonaws.com/fetch_and_run",
        "resourceRequirements": [
            {
                "type": "MEMORY",
                "value": "2000"
            },
            {
                "type": "VCPU",
                "value": "2"
            }
        ],
        "command": [
            "myjob.sh",
            "60"
        ],
        "jobRoleArn": "arn:aws:iam::123456789012:role/AWSBatchS3ReadOnly",
        "environment": [
            {
                "name": "BATCH_FILE_S3_URL",
                "value": "s3://amzn-s3-demo-source-bucket/myjob.sh"
            },
            {
                "name": "BATCH_FILE_TYPE",
                "value": "script"
            }
        ],
        "user": "nobody"
    }
}
```

# Parameter substitution
<a name="example-use-parameters"></a>

The following example job definition illustrates how to allow for parameter substitution and to set default values.

The `Ref::` declarations in the `command` section are used to set placeholders for parameter substitution. When you submit a job with this job definition, you specify the parameter overrides to fill in those values, such as the `inputfile` and `outputfile`. The `parameters` section that follows sets a default for `codec`, but you can override that parameter as needed.

For more information, see [Parameters](job_definition_parameters.md#parameters).

```
{
    "jobDefinitionName": "ffmpeg_parameters",
    "type": "container",
    "parameters": {"codec": "mp4"},
    "containerProperties": {
        "image": "my_repo/ffmpeg",
        "resourceRequirements": [
            {
                "type": "MEMORY",
                "value": "2000"
            },
            {
                "type": "VCPU",
                "value": "2"
            }
        ],
        "command": [
            "ffmpeg",
            "-i",
            "Ref::inputfile",
            "-c",
            "Ref::codec",
            "-o",
            "Ref::outputfile"
        ],
        "jobRoleArn": "arn:aws:iam::123456789012:role/ECSTask-S3FullAccess",
        "user": "nobody"
    }
}
```

# Test GPU functionality
<a name="example-test-gpu"></a>

The following example job definition tests if the GPU workload AMI described in [Use a GPU workload AMI](batch-gpu-ami.md) is configured properly. This example job definition runs the TensorFlow deep MNIST classifier [example](https://github.com/tensorflow/tensorflow/blob/r1.8/tensorflow/examples/tutorials/mnist/mnist_deep.py) from GitHub.

```
{
    "containerProperties": {
        "image": "tensorflow/tensorflow:1.8.0-devel-gpu",
        "resourceRequirements": [
            {
                "type": "MEMORY",
                "value": "32000"
            },
            {
                "type": "VCPU",
                "value": "8"
            }
        ],
        "command": [
            "sh",
            "-c",
            "cd /tensorflow/tensorflow/examples/tutorials/mnist; python mnist_deep.py"
        ]
    },
    "type": "container",
    "jobDefinitionName": "tensorflow_mnist_deep"
}
```

You can create a file with the preceding JSON text called `tensorflow_mnist_deep.json` and then register an AWS Batch job definition with the following command:

```
aws batch register-job-definition --cli-input-json file://tensorflow_mnist_deep.json
```

# Multi-node parallel job
<a name="example-mnp-job-definition"></a>

The following example job definition illustrates a multi-node parallel job. For more information, see [Building a tightly coupled molecular dynamics workflow with multi-node parallel jobs in AWS Batch](https://aws.amazon.com/blogs/compute/building-a-tightly-coupled-molecular-dynamics-workflow-with-multi-node-parallel-jobs-in-aws-batch/) in the *AWS Compute* blog.

```
{
  "jobDefinitionName": "gromacs-jobdef",
  "jobDefinitionArn": "arn:aws:batch:us-east-2:123456789012:job-definition/gromacs-jobdef:1",
  "revision": 6,
  "status": "ACTIVE",
  "type": "multinode",
  "parameters": {},
  "nodeProperties": {
    "numNodes": 2,
    "mainNode": 0,
    "nodeRangeProperties": [
      {
        "targetNodes": "0:1",
        "container": {
          "image": "123456789012.dkr.ecr.us-east-2.amazonaws.com/gromacs_mpi:latest",
          "resourceRequirements": [
              {
                  "type": "MEMORY",
                  "value": "24000"
              },
              {
                  "type": "VCPU",
                  "value": "8"
              }
          ],
          "command": [],
          "jobRoleArn": "arn:aws:iam::123456789012:role/ecsTaskExecutionRole",
          "ulimits": [],
          "instanceType": "p3.2xlarge"
        }
      }
    ]
  }
}
```