Bicep: Conditionally deploy a resource based on existence of a nullable object parameter

If you’re working with Bicep, you’ve probably encountered a situation where you need to conditionally deploy a resource based on the existence of a nullable object parameter. This can be a bit tricky, but don’t worry, we’ve got you covered!

The Scenario

Imagine you’re creating a Bicep template that deploys a virtual machine (VM) and a virtual network (VNet) to Azure. The VM requires a network interface card (NIC) to connect to the VNet, but the NIC is only needed if the VNet exists. If the VNet doesn’t exist, you don’t want to deploy the NIC.

In this scenario, you need to conditionally deploy the NIC based on the existence of the VNet. This is where nullable object parameters come into play.

Nullable Object Parameters

In Bicep, you can define nullable object parameters using the `?` symbol after the parameter type. For example:

param vNet object? = {
  id: '/subscriptions//resourceGroups//providers/Microsoft.Network/virtualNetworks/'
}

In this example, the `vNet` parameter is a nullable object that can be null or an object with an `id` property.

Conditional Deployment

To conditionally deploy a resource based on the existence of a nullable object parameter, you can use the `if` keyword in Bicep. The `if` keyword allows you to specify a condition that determines whether a resource should be deployed or not.

Here’s an example of how you can use the `if` keyword to conditionally deploy a NIC based on the existence of the VNet:

resource nic 'Microsoft.Network/networkInterfaces@2020-06-01' = if (vNet != null) {
  name: 'myNic'
  location: resourceGroup().location
  properties: {
    ipConfigurations: [
      {
        name: 'ipconfig1'
        properties: {
          subnet: {
            id: vNet.properties.subnets[0].id
          }
        }
      }
    ]
  }
}

In this example, the NIC resource is only deployed if the `vNet` parameter is not null. If `vNet` is null, the NIC resource is skipped.

Tips and Variations

Here are some tips and variations to keep in mind when using conditional deployment with nullable object parameters:

• Use the `!= null` syntax**: To check if a nullable object parameter is not null, use the `!= null` syntax. This ensures that the parameter is not null before attempting to deploy a resource.
• Use the `??` operator**: If you need to provide a default value for a nullable object parameter, use the `??` operator. For example: `vNet ?? { id: ‘/subscriptions//resourceGroups//providers/Microsoft.Network/virtualNetworks/‘ }`.
• Combine with other conditions**: You can combine the `if` keyword with other conditions to create more complex deployment logic. For example: `if (vNet != null && deployment().properties.templateLink.uri != ”) { … }`.

Best Practices

When using conditional deployment with nullable object parameters, keep the following best practices in mind:

1. Document your parameters**: Make sure to document your nullable object parameters clearly, including any default values and expected behavior.
3. Keep it simple**: Conditional deployment logic can get complex quickly. Keep your logic simple and easy to understand to avoid errors and maintenance issues.

Conclusion

Conditional deployment based on the existence of a nullable object parameter is a powerful feature in Bicep. By following the tips and best practices outlined in this article, you can create flexible and robust Bicep templates that adapt to different deployment scenarios.

Remember to always test your templates thoroughly and document your parameters clearly to avoid errors and misunderstandings.

Keyword	Description
`?` symbol	Used to define a nullable object parameter in Bicep.
`if` keyword	Used to conditionally deploy a resource based on a specified condition in Bicep.
`!= null` syntax	Used to check if a nullable object parameter is not null in Bicep.
`??` operator	Used to provide a default value for a nullable object parameter in Bicep.

By mastering conditional deployment with nullable object parameters, you can take your Bicep skills to the next level and create more efficient and flexible infrastructure deployments.

Happy deploying!

Frequently Asked Question

Get the clarity you need on deploying resources conditionally with Bicep!