Tip: Improving async experience with Pulumi
Recently we’ve been working a lot with Pulumi for automating our cloud environments. We’re building out our own management tool and creating Pulumi stack definitions in C#. One thing that quickly became a pain was working with the Inputs and Output and running into code that became way too nested, looking a lot like the old TPL or JavaScript Promises with .ContinueWith() or .then().
We’re building our stacks using the Pulumi function:
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PulumiFn.Create(async () =>
{
// Automate things...
});
Within the Action we set up the things we want to automate. A scenario we have, is to create a configuration object that contain the connection string from a MongoDB Cluster running with Atlas. The file generated is stored in an Azure file share we create with Pulumi.
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// Storage is an object being passed along with information about the Azure storage being used.
var getFileShareResult = GetFileShare.Invoke(new()
{
AccountName = storage.AccountName,
ResourceGroupName = resourceGroupName,
ShareName = storage.ShareName
});
// Cluster is an object holding the MongoDB cluster information.
var getClusterResult = GetCluster.Invoke(new()
{
Name = cluster.Name,
ProjectId = cluster.ProjectId
});
// Get the values we need to be able to write the connection string
getFileShareResult.Apply(fileShare =>
{
getClusterResult.Apply(clusterInfo =>
{
// Write the file with the connection string
return clusterInfo;
});
return fileShare;
});
In this sample we’re just interested in 2 values and still its quite a few lines of code and nested scopes.
To improve on this, we ended up creating a couple of extension methods that helps us write regular async/await based code.
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public static class OutputExtensionMethods
{
public static Task<T> GetValue<T>(this Output<T> output) => output.GetValue(_ => _);
public static Task<TResult> GetValue<T, TResult>(this Output<T> output, Func<T, TResult> valueResolver)
{
var tcs = new TaskCompletionSource<TResult>();
output.Apply(_ =>
{
var result = valueResolver(_);
tcs.SetResult(result);
return result;
});
return tcs.Task;
}
}
And for Input it would be the same:
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public static class InputExtensionMethods
{
public static Task<T> GetValue<T>(this Input<T> input) => input.GetValue(_ => _);
public static Task<TResult> GetValue<T, TResult>(this Input<T> input, Func<T, TResult> valueResolver)
{
var tcs = new TaskCompletionSource<TResult>();
input.Apply(_ =>
{
var result = valueResolver(_);
tcs.SetResult(result);
return result;
});
return tcs.Task;
}
}
With these we can now simplify the whole thing down to two lines of code:
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// Get the values we need to be able to write the connection string
var fileShareResult = await getFileShareResult.GetValue(_ => _);
var clusterInfo = await getClusterResult.GetValue(_ => _);
// Write the file with the connection string
...
We’re interested to hear if there are better ways already with the Pulumi SDK or if we’re going about this in the wrong way. Please leave a comment with any input, much appreciated.