serverless-sns-filter

A serverless plugin to add SNS Subscription filters to lambda events

• Installation
• Configuration
• Usage
• Limitations
• Contributing

For an example of a working application, see the integration-test

This plugin adds the following resources to your Serverless Cloudformation stack:

• A lambda function (invoked using CloudFormation Custom Resources) that adds an SNS Subscription Filter to a SNS Subscription
• An IAM Role, with a policy, to allow the above Lambda to create the SNS subscription filters including the following:

- Effect: Allow
           Action:
           - SNS:ListSubscriptions
           Resource:
           - Fn::Sub: arn:aws:sns:${AWS::Region}:${AWS::AccountId}:*
         - Effect: Allow
           Action:
           - SNS:setSubscriptionAttributes
           Resource:
             Fn::Sub: arn:aws:sns:${AWS::Region}:${AWS::AccountId}:*

Installation

Install the plugin:

npm install serverless-sns-filter

Add the plugin to your serverless.yml

plugins:
  - serverless-sns-filter

Configuration

Add a filter policy to your function under the events section:

functions:
  hello:
    handler: handler.hello
    events:
      - sns: ${self:custom.greeterTopic}
        # filter policy to accept messages with attrib_one values including "foo" OR "bar"
        filter:
          attrib_one:
            - foo
            - bar

Usage

SNS Subscription filters require SNS notifications to include MessageAttributes that the filters are matched against.

Example, NodeJS lambda that shall post a message that shall be received by the hello function above:

serverless.yml:

  sendMessage:
    handler: send.with_attribute
    environment:
      TOPIC_ARN: "${{self:custom.greeterTopicArn}}"

send.js:

const AWS = require('aws-sdk')
let sns = new AWS.SNS()

const publish_sns = (params, callback) => {
  sns.publish(params).promise().then(done => {
    console.log(JSON.stringify(done))
    callback(null,done)
  }).catch(error => {
    console.log(JSON.stringify(error))
    callback(error,"send failed")
  })
}

const with_attribute = (event, context, callback) => {
  const topicArn = process.env['TOPIC_ARN']
  console.log(`publishing to topic: ${topicArn}`)
  const params = {
    Message: 'should be received',
    MessageAttributes: {
      'attrib_one': {
        DataType: 'String',
        StringValue: 'foo'
      }
    },
    Subject: "Successful message",
    TopicArn: topicArn
  }

  publish_sns(params,callback)

}

module.exports = {
  with_attribute: with_attribute
}

Limitations

• SNS Subscription Filters cannot be removed at the present time. If you need to remove a filter, then remove the SNS subscription and re-create it without the filter definition.

• The plugin currently only supports a single SNS filter per function.

Contributing

• The person who found a bug should fix the bug by themself.
• If you find a bug and cannot fix it by yourself, send a pull request and attach test code to reproduce the bug, please.
• The person who want a new feature should implement it by themself.
• For above reasons, we accept pull requests only and disable issues.
• If you're not sure how to fix an issue, please create a pull request demonstrating a minimal viable complete example as a failing test.
• If you'd like to discuss about a new feature before implement it, make an empty commit and send a WIP pull request. But It is better that the WIP PR has some code than an empty commit.

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request

Publishing

cd plugin
yarn version
yarn run test
yarn run compile
npm login
npm publish