Invoke Lambda function by SNS message on local serverless-offline environment

Question

I'm using Serverless Framework & serverless-offline plugin to develop serverless web application locally, and trying to test the following procedure.

User pushes a button, which will call API
API will invoke Lambda function and it will publish a message to SNS topic
Several lambda functions subscribing the SNS topic will be invoked

serverless.yml

plugins:
  - serverless-offline
  - serverless-offline-sns

functions:
  publisher:
    handler: publisher.main
    events:
      - http:
          path: publish
          method: post
          cors: true
          authorizer: aws_iam

  subscriber:
    handler: subscriber.main
    events:
      - sns: test-topic

I tested it on AWS and it worked, but I don't know how to test it locally.

serverless-offline-sns does not support subscription by lambda for now.

serverless-offline-sns supports http, https, and sqs subscriptions. email, email-json, sms, application, and lambda protocols are not supported at this time. https://www.npmjs.com/package/serverless-offline-sns

I think this is a very common use case for serverless & event-driven architecture. How do you test this on local environment?

Theo Theo · Accepted Answer · 2019-01-07T13:41:58

I was able to simulate this offline recently using the following code/config

serverless.yml

functions:  
  ########## SNS SUBSCRIPTIONS ##########
  newUser:
    memorySize: 128
    timeout: 120
    handler: src/sns-subscribers/newUser.handler
    name: sns-newUser-dev
    events:
      - sns:
          arn: arn:aws:sns:ap-southeast-2:13XXXXXXXXXX:new-user-dev

plugins:
  - serverless-offline-sns
  - serverless-offline

custom:
  serverless-offline-sns:
    port: 4002 # a free port for the sns server to run on
    debug: true
    # host: 0.0.0.0 # Optional, defaults to 127.0.0.1 if not provided to serverless-offline
    # sns-endpoint: http://127.0.0.1:4002 # Optional. Only if you want to use a custom endpoint
    accountId: 13XXXXXXXXXX # Optional

Here's the code that triggers my offline lambda

trigger.js

const AWS = require('aws-sdk');

const sns = new AWS.SNS({
  endpoint: 'http://127.0.0.1:4002',
  region: 'ap-southeast-2',
});

sns.publish(
  {
    Message: 'new user!',
    MessageStructure: 'json',
    TopicArn: `arn:aws:sns:ap-southeast-2:13XXXXXXXXXX:new-user-dev`,
  },
  () => console.log('new user published'),
);

Run the trigger normally

node trigger.js

Note: In your example, the way you declared the sns subscription is not yet supported AFAIK.

events:
  - sns: test-topic # try using ARN and sending this to the next line

You can check this github issue for more info and updates.

Invoke Lambda function by SNS message on local serverless-offline environment

1 Answers