# Remote Procedure Calls Remote Procedure Calls are used to retrieve live data from a service for an input field. You can use RPCs to retrieve dynamic options in a field to clarify the expected input for a user. For example, selecting a country in a dropdown could trigger an RPC to retrieve corresponding states or cities. These requests are invoked while the user interacts with the modules when building a scenario. ## Types of RPCs * [Dynamic fields RPCs](https://developers.make.com/custom-apps-documentation/app-components/rpcs/dynamic-fields-rpc) generate dynamic fields inside a module. * [Dynamic options RPCs](https://developers.make.com/custom-apps-documentation/app-components/rpcs/dynamic-options-rpc) dynamically fill the fields in a module. * [Dynamic sample RPCs](https://developers.make.com/custom-apps-documentation/app-components/rpcs/dynamic-sample-rpc) replace hard-coded samples that might become outdated quickly. ## Components ### Communication Communication can be [request-less](https://developers.make.com/custom-apps-documentation/component-blocks/api/request-less-communication). As with modules, you can use [pagination](https://developers.make.com/custom-apps-documentation/component-blocks/api/pagination) in RPCs to iterate the records. ### Parameters [Parameters](https://developers.make.com/custom-apps-documentation/block-elements/parameters) from the modules are passed automatically to linked RPCs. ## Available IML variables The following IML variables are available to use anywhere in a module within IML strings.

Variable	Description
`now`	Current date and time with milliseconds in UTC timezone, in ISO 8601 format: `YYYY-MM-DDTHH:mm:ss.sssZ`.
`environment`	TBD
`temp`	Contains custom variables created using the `temp` directive. Example: `"temp": {` `"id": 123` `},` `"url": "/user/{{temp.id}}" // url === "/user/123"`
`parameters`	The module's input parameters collection (static and mappable).. The keys are the parameter `name` values, and the values are the data mapped by the user.
`connection`	The connection data collection (access token or API key and other values).
`common`	The collection defined in the app's Base common data. This will typically include the module 'timeout' limit and Client ID and secret when using OAuth 2.0 code grant connections.
`data`	The module's data collection.
`scenario`	TBD
`metadata.expect`	The module's raw mappable parameters as they were specified in the configuration.
`metadata.interface`	The module’s raw interface array the way you have specified it in the configuration.

Additional variables available within the `response` collection:

Variable	Description
`output`	When using the wrapper directive, the 'output' variable represents the result of the output directive.

Additional variables available when using the `iterate` directive, for example within the wrapper or [pagination](https://developers.make.com/custom-apps-documentation/component-blocks/api/pagination) collections:

Variable	Description
`iterate.container.first`	The first item of the iterated array.
`iterate.container.last`	The last item of the iterated array.

Additional variables available within the [pagination](https://developers.make.com/custom-apps-documentation/component-blocks/api/pagination) and [response](https://developers.make.com/custom-apps-documentation/component-blocks/api/handling-responses) collections:

Variable	Description
`body`	The response body received from the last request.
`headers`	The response headers received from the last request.
`item`	When using the `iterative` directive, this variable represents the current item that is being iterated.

Additional variables available in the webhook [attach](https://developers.make.com/custom-apps-documentation/app-components/webhooks/dedicated/attached) RPC.

Variable	Description
`webhook.id`	Internal webhook ID.
`webhook.url`	The webhook URL that you can use to automatically register the webhook in the external platform via the API, when it's supported.

Additional variables available in the webhook [detach](https://developers.make.com/custom-apps-documentation/app-components/webhooks/dedicated/not-attached) RPC and in the `expect` [mappable parameter](https://developers.make.com/custom-apps-documentation/component-blocks/mappable-parameters) and the [interface](https://developers.make.com/custom-apps-documentation/component-blocks/interface) section of an instant trigger module.

Variable	Description
`webhook`	The webhook’s data collection.

## Limits

Name	Total limit of...	Value
Max Execution Timeout	... seconds	40

Name	Recommended limit of ...	Value
Request Count	... calls performed by RPC	3
Record Count	... paginated records	3 * number of objects per page

## Best Practices Review the [best practices for RPCs](https://developers.make.com/custom-apps-documentation/best-practices/remote-procedure-calls).