Aws-cdk: Exporting DynamoDB Tables Across Stacks?

[mikecann]

The docs talk about how to share an S3 bucket across stacks but I cant seem to get it to work for DynamoDB Tables? There doesnt seem to be any "export" method.

Does this not work Universally? Is there a work-around (maybe cdk.Output)?

[eladb]

It's just a missing feature in the DynamoDB library.

As for a workaround, where do you plan to consume this imported table? You could technically use cdk.Output and cdk.FnImportValue to export the tableName from stack A and import it into stack B, but if your consumption point expects a dynamodb.Table, then you won't be able to convert your imported name into a construct. If you only need a name at the consumption point, then you should be fine.

[mikecann]

@eladb okay cool, thanks thats what I suspected. No worries ill work around it as you mention above.

[eladb]

Let’s keep this open until we implement this feature

[mikecann]

Oh apologies 👍 BTW im sure you are aware but UserPoolResource, UserPoolClientResource and IdentityPoolResource are all missing export too 😄

[eladb]

Yes, we are planning a more rigorous process to align our APIs :-)

[mikecann]

@eladb suppose im trying to export a table's Arn from one stack eg:

this.myTableArnOutput = new cdk.Output(this, "EventStoreTableArn", {
      value: eventStoreTable.tableArn
    });

I then want to use that Arn in a Role Policy in a different stack (in the same app):

myFunction.addToRolePolicy(
      new PolicyStatement()
        .addAction("dynamodb:Scan")
        .addResource(props.myTableArnOutput.makeImportValue())
    );

But I cant because makeImportValue() doesnt return the actual Arn only an import statement.

Do you have any suggestions here?

[eladb]

makeImportValue returns an token that resolves only at deploy-time, but since the value you are importing will eventually be a string (ARN), you can use makeImportValue().toString() to "stringify" the token so it can be "plugged in" anywhere strings go (in your case addResource(s)).

[mikecann]

@eladb oh cool, neat trick thanks, ill give that a shot tomorrow 😄

[rix0rrr]

Exports are actually transparent now, as long as your stacks are in the same app.

Closing.

[ranguard]

Any ETA on a release :) ?

[eladb]

@ranguard sorry for the delay. We will be able to publish a release next week.

[ranguard]

@eladb wonderful - thank you - I am looking forward to it :)

[kennu]

The new DynamoEventSource for Lambda expects a dynamodb.Table parameter. Is there some way to construct it from a table that is outside of the current stack? Or is there some alternative way to setup a DynamoEventSource?

[kennu]

Looking at the source code here, maybe DynamoEventSource could just allow configuring the tableStreamArn manually (instead of specifying a Table) in cases like this? https://github.com/awslabs/aws-cdk/blob/master/packages/%40aws-cdk/aws-lambda-event-sources/lib/dynamodb.ts#L36

[kennu]

Meanwhile I used this as a workaround to do the same thing as DynamoEventSource:

  new lambda.EventSourceMapping(this, 'DynamoDBEvent', {
    target: lambdaFunction,
    batchSize: 100,
    eventSourceArn: props.tableStreamArn,
    startingPosition: lambda.StartingPosition.Latest,
  })
  lambdaFunction.addToRolePolicy(new iam.PolicyStatement()
    .addAction('dynamodb:ListStreams')
    .addResource('*')
  )
  lambdaFunction.addToRolePolicy(new iam.PolicyStatement()
    .addActions('dynamodb:DescribeStream', 'dynamodb:GetRecords', 'dynamodb:GetShardIterator')
    .addResource(props.tableStreamArn)
  )