Hi I m trying to get a little bit better understanding of ho Pulumi Community #typescript

Hi, I'm trying to get a little bit better understa...

rough-hydrogen-27449

11/16/2021, 4:15 PM

Hi, I'm trying to get a little bit better understanding of how dynamic providers work. I noticed the following behavior and I'd like to develop a clear explanation for it. I have created a

Cluster

resource representing a Kafka cluster in Confluent Cloud:

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class Cluster extends pulumi.dynamic.Resource {
    public readonly endpoint!: pulumi.Output<string>;

    constructor(
        name: string,
        props: IClusterInputs,
        opts?: pulumi.CustomResourceOptions,
    ) {
        super(new ClusterProvider(), name, props, opts);
    }
}

and I've written a dynamic provider for this resource:

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class ClusterProvider implements pulumi.dynamic.ResourceProvider {
    async create(
        inputs: IClusterProviderInputs
    ): Promise<pulumi.dynamic.CreateResult> {
        const cmd = `kafka cluster create ${inputs.clusterName}`
            + ` --cloud aws`
            + ` --region ${inputs.region}`
            + ` --availability ${inputs.availability}`
            + ` --type ${inputs.clusterType}`
            + ` --environment ${inputs.environmentId}`;
        const result: IClusterCreateResult = await runConfluentCliCommand(cmd, true);
        return {
            id: result.id,
            outs: { // implements IClusterCreateOutputs
                endpoint: result.endpoint,
                environmentId: inputs.environmentId,
            },
        };
    }

    async update(
        _id: string,
        olds: IClusterProviderInputs,
        _news: IClusterProviderInputs
    ): Promise<pulumi.dynamic.UpdateResult> {
        return {outs: olds}; // FIXME: implement a real update method
    }

    async delete(
        id: string,
        props: IClusterCreateOutputs
    ): Promise<void> {
        const cmd = `kafka cluster delete ${id} --environment ${props.environmentId}`;
        return await runConfluentCliCommand(cmd, false);
    }
}

Then I construct a

Cluster

instance and

export

an object as a stack output:

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const cluster = new Cluster("MyCluster", { ... });

export let stackOutputs = {
    cluster_id: cluster.id,
    cluster_endpoint: cluster.endpoint,
};

When I spin up this stack and look at the stack outputs, the

cluster_id

is present but the

cluster_endpoint

is absent. I was able to determine that the

cluster.endpoint

value was

undefined

. To "fix" this, I did the following:

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export let stackOutputs = {
    cluster_id: cluster.id,
    cluster_endpoint: pulumi.output(cluster.endpoint),
};

Now the
cluster_endpoint
shows up in my stack outputs! Actually I'm not so sure... So, my question is: Why did wrapping this dynamic resource class member reference in a

pulumi.output(..)

cause it to be reified to a non

undefined

value? What is actually going on here? A corollary question: Why did I not have to also do this for the

id

? EDIT: I was a little confused, actually. My

pulumi.output(..)

edit did not, in fact, cause anything to show up in the stack output. The correct fix was to "initialize" the

endpoint

with an

undefined

in the call to

super(..)

in the

Cluster

constructor (see thread).

microscopic-florist-22719

11/16/2021, 5:09 PM

I think that I can answer this, though the answer for the

endpoint

bit isn’t particularly satisfying.

microscopic-florist-22719

11/16/2021, 5:11 PM

The constructor for the

pulumi.Resource

superclass needs to see all potential properties in the

props

bag, not just input properties. If the names of the output properties are not present in that bag, the

Resource

machinery can’t determine which output properties to expect.

microscopic-florist-22719

11/16/2021, 5:11 PM

So I think that if you change your code to this, things should work as you expect:

microscopic-florist-22719

11/16/2021, 5:12 PM

Copy code

class Cluster extends pulumi.dynamic.Resource {
    public readonly endpoint!: pulumi.Output<string>;

    constructor(
        name: string,
        props: IClusterInputs,
        opts?: pulumi.CustomResourceOptions,
    ) {
        super(new ClusterProvider(), name, { endpoint: undefined, ...props }, opts);
    }
}

microscopic-florist-22719

11/16/2021, 5:13 PM

The reason

pulumi.output(cluster.endpoint)

changed things is that it turned an

undefined

value into a resolved (but defined!)

pulumi.Output

value whose inner value is

undefined

microscopic-florist-22719

11/16/2021, 5:14 PM

w.r.t. `id`: you didn’t have to do anything special there because

id

is always defined by the SDK.

rough-hydrogen-27449

11/16/2021, 5:17 PM

Oh, yeah I think you're right. Why do we have to "initialize"

endpoint

like that in the dynamic resource constructor?

microscopic-florist-22719

11/16/2021, 6:09 PM

I think that it’s because without that initialization, it’s not possible for the constructor to know what the set of output properties is for the resource. IIRC there are problems with attempting to iterate over the properties defined on

this

(e.g. properties that are present on every object shouldn’t be considered output properties), but my JS/TS expertise may be failing me here (cc @microscopic-pilot-97530).

rough-hydrogen-27449

11/16/2021, 9:50 PM

Got it, that makes sense. Thanks.

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