Use Azure Batch CLI templates and file transfer

By using a Batch extension to Azure CLI, users can run Batch jobs without writing code.

Create and use JSON template files with Azure CLI to create Batch pools, jobs, and tasks. Use CLI extension commands to easily upload job input files to the storage account associated with the Batch account, and download job output files.

Overview

An extension to the Azure CLI enables Batch to be used end-to-end by users who are not developers. With only CLI commands, you can create a pool, upload input data, create jobs and associated tasks, and download the resulting output data. No additional code is required. Run the CLI commands directly or integrate them into scripts.

Batch templates build on the existing Batch support in the Azure CLI for JSON files to specify property values when creating pools, jobs, tasks, and other items. Batch templates add the following capabilities:

• Parameters can be defined. When the template is used, only the parameter values are specified to create the item, with other item property values specified in the template body. A user who understands Batch and the applications to be run by Batch can create templates, specifying pool, job, and task property values. A user less familiar with Batch and/or the applications only needs to specify the values for the defined parameters.

• Job task factories create one or more tasks associated with a job, avoiding the need for many task definitions to be created and significantly simplifying job submission.

Jobs typically use input data files and produce output data files. A storage account is associated, by default, with each Batch account. You can transfer files to and from this storage account using Azure CLI, with no coding and no storage credentials.

For example, ffmpeg is a popular application that processes audio and video files. Using the Azure Batch CLI extension, you could make it easier for a user to invoke ffmpeg to transcode source video files to different resolutions. The process might look like this:

• Create a pool template. The user creating the template knows how to call the ffmpeg application and its requirements; they specify the appropriate OS, VM size, how ffmpeg is installed (from an application package or using a package manager, for example), and other pool property values. Parameters are created so when the template is used, only the pool ID and number of VMs need to be specified.
• Create a job template. The user creating the template knows how ffmpeg needs to be invoked to transcode source video to a different resolution and specifies the task command line; they also know that there is a folder containing the source video files, with a task required per input file.
• An end user with a set of video files to transcode first creates a pool using the pool template, specifying only the pool ID and number of VMs required. They can then upload the source files to transcode. A job can then be submitted using the job template, specifying only the pool ID and location of the source files uploaded. The Batch job is created, with one task per input file being generated. Finally, the transcoded output files can be downloaded.

Installation

To install the Azure Batch CLI extension, first Install the Azure CLI 2.0.

Install the latest version of the Batch extension using the following Azure CLI command:

az extension add --name azure-batch-cli-extensions

For more information about the Batch CLI extension and additional installation options, see the GitHub repo.

To use the CLI extension features, you need an Azure Batch account and, for the commands that transfer files to and from storage, a linked storage account.

To log into a Batch account with the Azure CLI, see Manage Batch resources with Azure CLI.

Templates

Azure Batch templates are similar to Azure Resource Manager templates, in functionality and syntax. They are JSON files that contain item property names and values, but add the following main concepts:

• Parameters: Allow property values to be specified in a body section, with only parameter values needing to be supplied when the template is used. For example, the complete definition for a pool could be placed in the body and only one parameter defined for poolId; only a pool ID string therefore needs to be supplied to create a pool. The template body can be authored by someone with knowledge of Batch and the applications to be run by Batch; only values for the author-defined parameters must be supplied when the template is used. This lets users without any in-depth Batch and/or application knowledge use the templates.
• Variables: Allow simple or complex parameter values to be specified in one place and used in one or more places in the template body. Variables can simplify and reduce the size of the template, as well as make it more maintainable by having one location to change properties.
• Higher-level constructs: Some higher-level constructs are available in the template that are not yet available in the Batch APIs. For example, a task factory can be defined in a job template that creates multiple tasks for the job, using a common task definition. These constructs avoid the need to code to dynamically create multiple JSON files, such as one file per task, as well as create script files to install applications via a package manager.

Pool templates

Pool templates support the standard template capabilities of parameters and variables. They also support package references, which optionally allow software to be copied to pool nodes by using package managers. The package manager and package ID are specified in the package reference. By declaring one or more packages, you avoid creating a script that gets the required packages, installing the script, and running the script on each pool node.

The following is an example of a template that creates a pool of Linux VMs with ffmpeg installed. To use it, supply only a pool ID string and the number of VMs in the pool:

{
    "parameters": {
        "nodeCount": {
            "type": "int",
            "metadata": {
                "description": "The number of pool nodes"
            }
        },
        "poolId": {
            "type": "string",
            "metadata": {
                "description": "The pool ID "
            }
        }
    },
    "pool": {
        "type": "Microsoft.Batch/batchAccounts/pools",
        "apiVersion": "2016-12-01",
        "properties": {
            "id": "[parameters('poolId')]",
            "virtualMachineConfiguration": {
                "imageReference": {
                    "publisher": "Canonical",
                    "offer": "UbuntuServer",
                    "sku": "20.04-LTS",
                    "version": "latest"
                },
                "nodeAgentSKUId": "batch.node.ubuntu 20.04"
            },
            "vmSize": "STANDARD_D3_V2",
            "targetDedicatedNodes": "[parameters('nodeCount')]",
            "enableAutoScale": false,
            "taskSlotsPerNode": 1,
            "packageReferences": [
                {
                    "type": "aptPackage",
                    "id": "ffmpeg"
                }
            ]
        }
    }
}

If the template file was named pool-ffmpeg.json, then invoke the template as follows:

az batch pool create --template pool-ffmpeg.json

The CLI prompts you to provide values for the poolId and nodeCount parameters. You can also supply the parameters in a JSON file. For example:

{
  "poolId": {
    "value": "mypool"
  },
  "nodeCount": {
    "value": 2
  }
}

If the parameters JSON file was named pool-parameters.json, then invoke the template as follows:

az batch pool create --template pool-ffmpeg.json --parameters pool-parameters.json

Job templates

Job templates support the standard template capabilities of parameters and variables. They also support the task factory construct, which creates multiple tasks for a job from one task definition. Three types of task factory are supported: parametric sweep, task per file, and task collection.

The following is an example of a template that creates a job to transcode MP4 video files with ffmpeg to one of two lower resolutions. It creates one task per source video file. See File groups and file transfer for more about file groups for job input and output.

{
    "parameters": {
        "poolId": {
            "type": "string",
            "metadata": {
                "description": "The name of Azure Batch pool which runs the job"
            }
        },
        "jobId": {
            "type": "string",
            "metadata": {
                "description": "The name of Azure Batch job"
            }
        },
        "resolution": {
            "type": "string",
            "defaultValue": "428x240",
            "allowedValues": [
                "428x240",
                "854x480"
            ],
            "metadata": {
                "description": "Target video resolution"
            }
        }
    },
    "job": {
        "type": "Microsoft.Batch/batchAccounts/jobs",
        "apiVersion": "2016-12-01",
        "properties": {
            "id": "[parameters('jobId')]",
            "constraints": {
                "maxWallClockTime": "PT5H",
                "maxTaskRetryCount": 1
            },
            "poolInfo": {
                "poolId": "[parameters('poolId')]"
            },
            "taskFactory": {
                "type": "taskPerFile",
                "source": {
                    "fileGroup": "ffmpeg-input"
                },
                "repeatTask": {
                    "commandLine": "ffmpeg -i {fileName} -y -s [parameters('resolution')] -strict -2 {fileNameWithoutExtension}_[parameters('resolution')].mp4",
                    "resourceFiles": [
                        {
                            "blobSource": "{url}",
                            "filePath": "{fileName}"
                        }
                    ],
                    "outputFiles": [
                        {
                            "filePattern": "{fileNameWithoutExtension}_[parameters('resolution')].mp4",
                            "destination": {
                                "autoStorage": {
                                    "path": "{fileNameWithoutExtension}_[parameters('resolution')].mp4",
                                    "fileGroup": "ffmpeg-output"
                                }
                            },
                            "uploadOptions": {
                                "uploadCondition": "TaskSuccess"
                            }
                        }
                    ]
                }
            },
            "onAllTasksComplete": "terminatejob"
        }
    }
}

If the template file was named job-ffmpeg.json, then invoke the template as follows:

az batch job create --template job-ffmpeg.json

As before, the CLI prompts you to provide values for the parameters. You can also supply the parameters in a JSON file.

Use templates in Batch Explorer

You can upload a Batch CLI template to the Batch Explorer desktop application to create a Batch pool or job. You can also select from predefined pool and job templates in the Batch Explorer Gallery.

To upload a template:

1. In Batch Explorer, select Gallery > Local templates.
2. Select, or drag and drop, a local pool or job template.
3. Select Use this template, and follow the on-screen prompts.

File groups and file transfer

Most jobs and tasks require input files and produce output files. Usually, input files and output files are transferred, either from the client to the node, or from the node to the client. The Azure Batch CLI extension abstracts away file transfer and utilizes the storage account that you can associate with each Batch account.

A file group equates to a container that is created in the Azure storage account. The file group may have subfolders.

The Batch CLI extension provides commands to upload files from client to a specified file group and download files from the specified file group to a client.

az batch file upload --local-path c:\source_videos\*.mp4
    --file-group ffmpeg-input

az batch file download --file-group ffmpeg-output --local-path
    c:\output_lowres_videos

Pool and job templates allow files stored in file groups to be specified for copy onto pool nodes or off pool nodes back to a file group. For example, in the job template specified previously, the file group ffmpeg-input is specified for the task factory as the location of the source video files copied down to the node for transcoding. The file group ffmpeg-output is the location where the transcoded output files are copied from the node running each task.

Summary

Template and file transfer support have currently been added only to the Azure CLI. The goal is to expand the audience that can use Batch to users who do not need to develop code using the Batch APIs, such as researchers and IT users. Without coding, users with knowledge of Azure, Batch, and the applications to be run by Batch can create templates for pool and job creation. With template parameters, users without detailed knowledge of Batch and the applications can use the templates.

Try out the Batch extension for the Azure CLI and provide us with any feedback or suggestions, either in the comments for this article or via the Batch Community repo.

Next steps

• View detailed installation and usage documentation, samples, and source code in the Azure GitHub repo.
• Learn more about using Batch Explorer to create and manage Batch resources.