# AWS.Compute.UserData
<a name="node-compute-user-data"></a>

AWS TNB supports launching Amazon EC2 instances with custom user data, through the UserData node in Network Service Descriptor (NSD). For more information about custom user data, see [User data and shell scripts](https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/user-data.html#user-data-shell-scripts) in the *Amazon EC2 User Guide*.

During network instantiation, AWS TNB provides the Amazon EC2 instance registration to the cluster through a user-data script. When custom user data is also provided, AWS TNB merges both scripts and passes them on as a [multimime](https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/user-data.html#user-data-mime-multi) script to Amazon EC2. The custom user-data script is run prior to the Amazon EKS registration script.

To use custom variables in the user-data script, add an exclamation mark `!` after the open curly brace `{`. For example, to use `MyVariable` in the script, enter: `{!MyVariable}`

**Note**  
AWS TNB supports user-data scripts up to 7 KB in size.
Because AWS TNB uses CloudFormation to process and render the `multimime` user-data script, ensure that the script adheres to all CloudFormation rules.

## Syntax
<a name="node-compute-user-data-syntax"></a>

```
tosca.nodes.AWS.Compute.UserData:
  properties:
    implementation: String
    content\$1type: String
```

## Properties
<a name="node-compute-user-data-properties"></a>

 `implementation`    
The relative path to the user data script definition. The format must be: `./scripts/script_name.sh`  
Required: Yes  
Type: String

 `content_type`    
Content type of the user data script.  
Required: Yes  
Type: String  
Possible values: `x-shellscript`

## Example
<a name="node-compute-user-data-example"></a>

```
ExampleUserData:
  type: tosca.nodes.AWS.Compute.UserData
  properties:
    content_type: "text/x-shellscript"
    implementation: "./scripts/customUserData.sh"
```