AWS CDK Subscribe Multiple Lambdas to Same SNS Queue

Question

I want to do the first approach listed here, where in order to trigger various lambda functions to run when a single S3 bucket is updated, I would put an SNS queue in between.

Currently I have each Lambda as a stack, and I would prefer to keep it that way, especially since I have separate pipeline stages I need to separate anyways. However, I want to be able to make them all share the same SNS queue. What would be the best way to do this?

From my thinking, the best way to approach would be to create an "sns queue stack" that creates the topic, then pass that topic into each lambda stack and subscribe the lambda functions that way, but I'm still unsure of the best way to deploy this sns queue stack.

This is most confusing to me in regards to using a deployment pipeline in the CDK. I have multiple pipeline stages, each with multiple deployment groups and multiple lambda stacks in said deployment groups. How should I add in this stack to ensure it is deployed properly?

One guess I have would be to add it into the very first stage in the very first deployment group before all other stacks and then it should work for every other stage, but I'm not sure if this is a way that would work.

you have each lambda as a stack in single cdk project or you have multiple cdk projects? — Balu Vyamajala

Balu Vyamajala Balu Vyamajala · Accepted Answer · 2021-03-17T02:22:18

We can use two approaches.

Multiple stacks in single CDK Project:

We have single CDK project with multiple stacks with in the same project. For example we have 1 stack with SNS topic and 1 stack for each lambda and its SNS subscription. We can use sns topic name accross stacks like documented here

const snsStack = new MySnsStack(app, 'my-sns-stack');

// each stack takes property topic as input, which behind the scenes perform cloudformation export and import.
 new MyLambdaOne(app, 'Stack2', {
  topic: snsStack.topic
});
 new MyLambdaTwo(app, 'Stack2', {
  topic: snsStack.topic
});

All we need to do is cdk deploy and stacks are arranged and deployed in proper sequence. i.e. sns stack first and rest of the lambda stacks next based on references.

Multiple CDK Projects :

We have 1 stack per cdk project. so, we have multiple CDK projects to maintain. We then have to manually export topic Arn using cfnOutput from the first stack and import topic arn in other stacks using Fn.ImportValue. Then we need to run multiple deployes cdk deploy MySnsStack, cdk deploy MyLambdaStack , etc. separately. First the sns stack, rest of them in parallel.

AWS CDK Subscribe Multiple Lambdas to Same SNS Queue

1 Answers