Lambda Alias AppSync Resolvers

[romanfq]

Allow a Lambda Data Source that can point to an alias

Use Case

When using Provisioned Concurrency today in a Lambda- for lower cold-starts- an alias gets created, which is usually called live. The ARN of this alias is that of the Lambda Function with a :live suffix.

Now, when a lambda data source is added to an AppSync API, the data source is pointing to the Lambda function and not the the alias, and then calls from AppSync don't call the alias but the $LATEST version of the function (no idea why this doesn't work). This defeats Provisioned Concurrency.

There's a manual workaround: after deploying the AppSync API and the Lambda, you can go to the console and

• Adjust the resolver arn to point to the alias
• Adjust the IAM policy that allows AppSync calling into Lambda to point to the alias

Proposed Solution

Add native support to the CDK to generate an Alias datasource, similar to

const alias = ...
const aliasDs: LambdaAliasDataSource = this.appSync.addLambdaAliasDataSource("LambdaDataSource", alias);

or simply add an override to addLambdaDataSource that allows to supply an alias

const alias = ...
const lambdaDs: LambdaDataSource = this.appSync.addLambdaAliasDataSource("LambdaDataSource", lambdaFunction, alias);

I tried to simulate the same by creating my own types under the DataSource hierarchies (i.e. creating a new sub-type of BackedDataSource and forcing a grantInvoke on the IAM role for the alias but it didn't work well- I might post repro code at some later stage.

• [x] :wave: I may be able to implement this feature request
• [ ] :warning: This feature might incur a breaking change

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This is a :rocket: Feature Request

[otaviomacedo]

Hi, @romanfq

I am unassigning and marking this issue as p2, which means that we are unable to work on this immediately.

We use +1s to help prioritize our work, and are happy to revaluate this issue based on community feedback. You can reach out to the cdk.dev community on Slack to solicit support for reprioritization.

[BryanPan342]

@romanfq I'm surprised you can't just run

const alias = ...
api.addLambdaDataSource('LambdaDataSource', alias);

addLambdaDataSource takes IFunction as the property type which Version and Alias extend from...

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