How to add subscription filter to SNS topic in CDK

Question

I am having this problem in CDK. I have a lambda triggered by a SNS Topic (receiving events from a S3 bucket) but right now its executing on every single message being delivered to the SNS Topic. I want the Lambda to only execute on specific bucket name, file ending and PutObject operations.

I know how to connect SNS to my lambda, just not with the filter:

    const myTopic = new sns.Topic(this, "Topic", {});

    myTopic.addToResourcePolicy(new iam.PolicyStatement({
      effect: iam.Effect.ALLOW,
      actions: ["sns:Publish"],
      resources: [myTopic.topicArn],
      principals: [new iam.AccountPrincipal('XXXXXXXXX')]
    }))
    
     const snsEventSource = new lambdaEventSources.SnsEventSource(myTopic);
     myLambda.addEventSource(snsEventSource)

I am not sure how to add the filter, I have tried playing around with sns.SubscriptionFilter without any luck

Answer 1

I got it to work with code like this:

    const myTopic = new sns.Topic(this, "Topic", {});
    myTopic.addToResourcePolicy(new iam.PolicyStatement({
      effect: iam.Effect.ALLOW,
      actions: ["sns:Publish"],
      resources: [myTopic.topicArn],
      principals: [new iam.AccountPrincipal('XXXXXXXXX')]
    }))

    myLambda.grantInvoke(new iam.ServicePrincipal('sns.amazonaws.com'))
    
    myTopic.addSubscription(new subs.LambdaSubscription(myLambda, {
          filterPolicy: {
            S3_BUCKET_NAME: sns.SubscriptionFilter.stringFilter({allowlist: ['myBucket']}),
            S3_EVENT_NAME: sns.SubscriptionFilter.stringFilter({allowlist: ['ObjectCreated:Put']})
          }
        }))