Cloud scripts and cloud script templates
Summarize
Summary of Cloud scripts and cloud script templates
In the Cloud Provisioning and Governance application of ServiceNow, script execution is managed through two key components: cloud scripts and cloud script templates. These scripts enable automation and customization within blueprints, resource blocks, OS profiles, and policy scripts to control request form attributes. Cloud scripts are JavaScript-based and leverage platform features, while cloud script templates are executable scripts targeted at virtual machines in various formats such as Shell, PowerShell, or CloudInit.
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Cloud Scripts
Cloud scripts are simple JavaScript functions that access parameters to customize behavior. They have built-in access to the templateResolver object, enabling retrieval and parameter substitution of cloud script templates. Parameters within cloud scripts have names, default values, and override values, which can be literal strings, resource block parameters, or script expressions.
Cloud scripts allow dynamic customization by modifying template attributes programmatically. For example, you can change parameter values or query ServiceNow tables to set attributes before running templates.
Cloud Script Templates
Cloud script templates are the actual executable scripts sent to target virtual machines for execution. They can be created in various script types depending on the execution environment, and must be associated with a cloud script to be used.
Use Cases of Cloud Scripts as CloudInit
- Image Level: Assign cloudinit scripts to specific images. When an OS profile with that image is selected, the default cloud script executes automatically.
- OS Profile Level: Associate cloud scripts to OS profiles either generically or for specific images. These mappings override image-level scripts and can be further customized with parameter overrides.
- Resource Blocks: While mapping cloud scripts to OS profiles, you can target execution for specific resource blocks and resource aliases within a blueprint.
Use Cases of Cloud Scripts as Postinit Scripts
Cloud scripts can be executed as post-initialization operations within resource blocks by adding an ExecuteScript operation. This operation selects a script from a pool and allows parameter overrides via a JSON map using the ScriptParameters attribute, supporting all expressions available in Cloud Management.
In the Cloud Provisioning and Governance application, script execution is divided into cloud scripts and cloud script templates. Use scripts in blueprints, resource blocks, OS profiles, and use policy scripts to set request form attributes. Policy scripts cannot override user data.
Cloud scripts
function evaluateTemplate() {
// Template Resolver is a helper function which we will use to fetch a template and replace its parameters,
// var templateResolver=new TemplateResolver(); this comes inbuild
// templateAttributes below will passed from the user.
var listDir=templateResolver.getTemplate('Install',templateAttributes);
return listDir;
}
Each cloud script contains certain parameters. Parameters are the attributes that you want to access. A parameter contains a name, a default value, and an override value. The default value can be a string literal, a resource block parameter or a complex script expression used in resource blocks.
A cloud script, by default, has access to the templateResolver object. The templateResolver object has, by default, a getTemplate method, whose first parameter is the cloud script template name. templateAttributes are the cloud script parameters created as part of a cloud script. If needed, customizations can be done in templateAttributes. As an example, see the following code snippet if the value of DevName parameter needs to be changed from John to Emily.
function evaluateTemplate() {
// Template Resolver is a helper function which we will use to fetch a template and replace its parameters,
// var templateResolver=new TemplateResolver(); this comes inbuild
// templateAttributes below will passed from the user.
templateAttributes['DevName'] = 'Emily';
var customNodeName;
var now_GR = new GlideRecord('some_custom_table_to_query');
gr.addQuery('some_parameter','some_value');
gr.query();
if(gr.next())
customNodeName=gr.getValue('some_custom_node_name');
templateAttributes['NodeName'] = customNodeName;
var listDir=templateResolver.getTemplate('Install',templateAttributes);
return listDir;
}
evaluateTemplate();
Cloud script templates
Cloud script templates are actual executables which are passed to target a virtual machine for execution. Cloud templates can be of any type (Shell/PowerShell/CloudInit) depending on the execution context. You need to create a cloud template first and then associate it with a cloud script.
Cloud scripts as CloudInit
- Image level: At the time of creating a cloud script, you can specify an image against
which this script should be executed. Once an OS profile which contains this specific
image gets selected, the default cloud script against this image is executed. In the
example below, an Apache cloud script is associated with a particular image.
- OS profile level: You can run a cloudinit against a specific cloud provider and
against a specific AMI/image. You can also be generic and associate a cloudinit to an OS
profile, irrespective of the underlying image. In the following example, multiple images
are associated with the OS profile. You can map any cloud script to the OS profile in
the Cloud Script OS Profile Mappings tab. The mapping of a cloud script with an OS
profile takes precedence over the image-level cloud script association.
In this example, the Apache cloud script is mapped to the Centos OS profile. If needed, you can override the script parameters in the OS Profile Mapping Overrides section. - Resource blocks: While mapping a cloud script to an OS profile, you can choose whether to execute the cloud script for a specific resource block used in a blueprint and against a particular resource alias. See Create an OS profile.
Cloud scripts as Postinit
You can use cloud scripts as Postinit scripts in a resource block. Once you create a resource block with a virtual machine to be provisioned, you can add an ExecuteScript operation. The ExecuteScript operation takes a script parameter (a pool of cloud scripts) and you can select any script to execute. Use the ScriptParameters attribute in the ExecuteScript operation to override any script parameter. You can provide a JSON map of script parameter and its override value. All expressions that are supported by Cloud Management work in the ScriptParamters attribute.