# Defining job template parameters
<a name="use-job-template-parameters"></a>

Job template parameters allow you to specify variables in the job template. Values for these parameter variables will need to be specified when starting a job run using that job template. Job template parameters are specified in `${parameterName}` format. You can choose to specify any value in a `jobTemplateData` field as a job template parameter. For each of the job template parameter variables, specify its data type (`STRING` or `NUMBER`) and optionally a default value. The example below shows how you can specify job template parameters for entry point location, main class, and S3 log location values.

**To specify entry point location, main class, and Amazon S3 log location as job template parameters**

1. Create a `create-job-template-request.json` file and specify the required parameters for your job template, as shown in the following example JSON file. For more information about the parameters, see the [CreateJobTemplate](https://docs.aws.amazon.com/emr-on-eks/latest/APIReference/Welcome.html) API.

   ```
   {
      "name": "mytemplate",
      "jobTemplateData": {
           "executionRoleArn": "{{iam_role_arn_for_job_execution}}", 
           "releaseLabel": "emr-6.7.0-latest",
           "jobDriver": {
               "sparkSubmitJobDriver": { 
                   "entryPoint": "${EntryPointLocation}",
                   "entryPointArguments": [ "{{argument1}}","{{argument2}}",...],
                   "sparkSubmitParameters": "--class ${MainClass} --conf spark.executor.instances=2 --conf spark.executor.memory=2G --conf spark.executor.cores=2 --conf spark.driver.cores=1"
               }
           },
           "configurationOverrides": {
               "applicationConfiguration": [
                   {
                       "classification": "spark-defaults", 
                       "properties": {
                            "spark.driver.memory":"2G"
                       }
                   }
               ], 
               "monitoringConfiguration": {
                   "persistentAppUI": "ENABLED", 
                   "cloudWatchMonitoringConfiguration": {
                       "logGroupName": "{{my_log_group}}", 
                       "logStreamNamePrefix": "{{log_stream_prefix}}"
                   }, 
                   "s3MonitoringConfiguration": {
                       "logUri": "${LogS3BucketUri}"
                   }
               }
           },
           "parameterConfiguration": {
               "EntryPointLocation": {
                   "type": "STRING"
               },
               "MainClass": {
                   "type": "STRING",
                   "defaultValue":"{{Main}}"
               },
               "LogS3BucketUri": {
                   "type": "STRING",
                   "defaultValue":"s3://{{my_s3_log_location}}/"
               }
           }
       }
   }
   ```

1. Use the `create-job-template` command with a path to the `create-job-template-request.json` file stored locally or in Amazon S3.

   ```
   aws emr-containers create-job-template \ 
   --cli-input-json file:{{//./create-job-template-request.json}}
   ```

**To start a job run using job template with job template parameters**

To start a job run with a job template containing job template parameters, specify the job template id as well as values for job template parameters in the `StartJobRun` API request as shown below.

```
aws emr-containers start-job-run \
--virtual-cluster-id {{123456}} \
--name {{myjob}} \
--job-template-id {{1234abcd}} \
--job-template-parameters '{"EntryPointLocation": "{{entry_point_location}}","MainClass": "{{ExampleMainClass}}","LogS3BucketUri": "s3://{{example_s3_bucket}}/"}'
```