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Elastic Compute Service

Appendix

Overview of custom template syntax

Template syntax defines the template structure, including parameters, execution order, constraints on input/output fields, and validation rules. Volcano Engine allows you to define custom templates in JSON format. The following template structure is supported.

Parameter	Description
FormatVersion	Optional. The engine version. The default value is 0.2.
Description	Optional. The description of details such as the usage and purpose of the template.
Parameters	Optional. Defines the list of parameters used during template execution. Learn more.
Tasks	Required. The Tasks parameter is the most important component of a template. Each task defines a specific action to be executed. These actions are defined and implemented by the Orchestration service. Learn more. tip If multiple tasks exist, they are executed sequentially by default, following the top-to-bottom order. If a task is a loop task, concurrent sub-executions may occur within that task.
Outputs	Optional. The Outputs parameter defines key data produced after template execution and can reference the output of a task (by specifying the task name). Learn more.

Parameters description

The Parameters parameter defines the list of parameters used during template execution, including parameter names, types, and default values.

tip

If no default value is specified, the default value is the zero value of the parameter type (that is, the default initial value for that type).

Tasks description

The Tasks parameter is the most important component of a template. Each task defines a specific action to be executed. These actions are defined and implemented by the Orchestration service, and include atomic actions and cloud product-specific actions. Learn more.

tip

If multiple tasks exist, they are executed sequentially by default, following the top-to-bottom order. If a task is a loop task, concurrent sub-executions may occur within that task.

The number of tasks specified by the Tasks parameter in a custom template cannot exceed 30.

Tasks structure

Parameter	Required	Description
Name	Yes	The task name. Valid values: It can contain only letters, digits, hyphens (-), and underscores (_). It can contain 1 to 200 characters in length.
Description	No	The description that explains the purpose of the current task.
Action	Yes	The name of the action.
Timeout	No	Optional. The timeout period. The maximum timeout period is 600 seconds.
Parameters	No	The set of parameters required for the execution of the current task. The parameter values can be obtained by using JQ expressions. The required parameters are determined by the specific actions. For more information, see the "Actions" topic.
Outputs	No	The output definition of the current task, which can be used as the input for subsequent tasks or as the output of the template. Learn more. Type: The field type. Value: The field value.
Loop	No	The task loop. For more information, see Loop tasks.
OnError/OnSuccess	No	The subsequent operation when the task execution result is either failure or success. Value: OnError: Used to define the operation when task execution fails. When you set OnError to: VOS::END (default): The entire execution is terminated. VOS::Next: The next task is executed. OnSuccess: Used to define the operation when task execution succeeds. When you set OnSuccess to: VOS::END: The entire execution is terminated. VOS::Next (default): The next task is executed.

Loop tasks

VolcanoEngine provides a special attribute called "loop task" for the Tasks parameter. In a loop task, batch tasks are automatically generated and executed based on the item list specified by LoopItem. You can specify parameters such as execution batches and concurrency to enable large-scale task scheduling.

tip

Tasks for API actions and cloud product actions support looping, while tasks for functional actions such as Trigger and Sleep do not support looping.

Loop tasks support concurrent execution. However, when running in single-step mode, looped tasks are automatically adjusted to execute sequentially with no concurrency.

A loop task is equivalent to executing the same task multiple times with different input parameters.

VOS::LoopItem is a built-in variable used to specify that the parameter value is sourced from the loop items defined by the Loop field. For example, each element in {{ .InstanceIds }} is retrieved sequentially by using this variable.

Limits

The maximum number of loop items is currently 1,000.

Syntax structure

Parameter description

LoopItem: The loop object.

Outputs: The output of a single task.

Concurrency control

Mode: Executes tasks by group. You can set this parameter to Batch or Concurrency and specify the maximum number of errors.

Batch: Divides the total number of tasks into batches. Parameter Description:

BatchSize: The number of items in each batch. The default value is 1.

BatchPauseOption: Specifies whether a pause is required between batches. By default, the next batch is executed automatically.

MaxErrorsValue: The maximum number of errors.

Concurrency: Concurrent execution.

ConcurrencySize: The concurrency level.

MaxErrorsValue: The maximum number of errors.

Outputs description

The Outputs parameter retrieves key data after template execution. It ensures users can accurately obtain required results such as post-operation instance statuses, task IDs, and execution time.

Example:

Last updated: 2026.06.18 17:48:27