How to generate environment-dependent Bicep expressions from Aspire?

[jakub-swastek]

Hi Aspire Team,

We're using Aspire to provision Azure resources, including Azure Cosmos DB.

For Cosmos DB we'd like to configure the backup policy dynamically based on the deployment environment:

• Production -> Continuous30Days
• Non-production environments -> Continuous7Days

If deployment is performed exclusively through the Aspire CLI, handling this in C# is straightforward. However, we also generate Bicep locally and commit it as part of our workflow. During CI/CD, we regenerate the Bicep and compare it with the committed version to detect Aspire version mismatches (and then deploy via Aspire CLI).

While looking for a solution, I found the BicepExpression type:

https://learn.microsoft.com/en-us/dotnet/api/azure.provisioning.expressions.bicepexpression?view=azure-dotnet

However, I haven't been able to find much documentation or any practical examples showing how it can be used within Aspire/Azure Provisioning resources to emit conditional expressions into the generated Bicep and in a same time handle C# value assignment.

Is this a supported scenario? I'm starting to wonder whether Bicep generation is overengineering this use case.

Thanks!

[John Karam (johnkaram02)]

Yes, this works, and you don't need to hand-write Bicep. Azure.Provisioning.Expressions has the pieces you need (ConditionalExpression, BinaryExpression, StringLiteralExpression), and any BicepValue<T> property accepts an expression in place of a literal. Add a Bicep parameter for the environment, use it in a ternary, and feed it from an Aspire parameter:

using Azure.Provisioning;
using Azure.Provisioning.CosmosDB;
using Azure.Provisioning.Expressions;

var environmentName = builder.AddParameter("environmentName");

builder.AddAzureCosmosDB("cosmos")
    .WithParameter("environmentName", environmentName)
    .ConfigureInfrastructure(infra =>
    {
        var envName = new ProvisioningParameter("environmentName", typeof(string));
        infra.Add(envName);

        var account = infra.GetProvisionableResources().OfType<CosmosDBAccount>().Single();
        account.BackupPolicy = new ContinuousModeBackupPolicy
        {
            ContinuousModeTier = new ConditionalExpression(
                new BinaryExpression(envName.Value.Compile(), BinaryBicepOperator.Equal, new StringLiteralExpression("Production")),
                new StringLiteralExpression("Continuous30Days"),
                new StringLiteralExpression("Continuous7Days")),
        };
    });

I ran this with Aspire 13.6.4 (--operation publish --publisher default). The generated cosmos.module.bicep contains:

param environmentName string
...
    backupPolicy: {
      type: 'Continuous'
      continuousModeProperties: {
        tier: (environmentName == 'Production') ? 'Continuous30Days' : 'Continuous7Days'
      }
    }

and the manifest wires the parameter through:

"cosmos": {
  "type": "azure.bicep.v0",
  "path": "cosmos.module.bicep",
  "params": { "environmentName": "{environmentName.value}" }
}

That gives you what you're after on both sides:

• The committed Bicep is identical for every environment, so your "regenerate and diff" check in CI keeps working. The environment only shows up as a parameter value, not as different template text.
• The value still comes from C#/config at deploy time: aspire deploy resolves environmentName like any other Aspire parameter (Parameters:environmentName in config/user secrets, an env var, or the prompt). So the same AppHost deploys either tier.

One thing to avoid: branching in C# (if (builder.Environment.IsProduction()) ... Continuous30Days) and committing the result. That bakes one environment's value into the template, and your diff would flip depending on which environment generated it. The expression approach keeps the decision inside Bicep.

To compare on something other than equality, BinaryBicepOperator also has EqualIgnoreCase, NotEqual, And, Or, etc. EqualIgnoreCase is worth considering here, so production vs Production doesn't silently pick the 7-day tier.