Appsync Invoke lambda after response?

1
votes

Example Problem:

A user can post their own articles on our website. However, each user can only post 5 articles and when they post their 5th article, we want to send them an email.

Using revolvers only, is it possible to return the mutation response on time and then lazily/async invoke a lambda function that sends an email to the user?

1
aws-lambdagraphqlaws-appsyncaws-amplify

1 Answers

3
votes

Yes, that should be very possible. It depends a bit on what kind of resolver you want to use. If you were using a Lambda data source:

  • As you mentioned, Lambda invocations can be asynchronous, so you could execute one inside a Lambda resolver and see minimal additional overhead.
  • You could use Lambda event sourcing. For example, earlier this year, Lambda launched SQS event-based Lambda invocations. What that means is, your Lambda resolver would put a message with some event context into an SQS queue (such as account info, email address...etc.), and then you'd have a Lambda that listens to that queue. It automagically polls, so it would invoke immediately and parse that message, and you'd send the email from that.
  • There's additional Lambda event sources that you could find helpful based on personal preferences/application needs, all of which are visible in the docs. Specifically, you might find SNS and/or Kinesis to be viable options. Conceptually they're the same - your resolver pushes a message into some AWS service, and the event-driven Lambda will automatically be invoked.

If you were using a DynamoDB data source:

  • You could set up DynamoDB streams on your table and hook up an event-driven Lambda that listens to that stream.

In any case, you might find pipeline resolvers to be useful. It allows you to set up a linear, synchronous chain of resolvers to solve some more complex problems. You could have an initial Lambda function/DDB lookup to get the number of posts (and potentially fail if someone is at their limit), then a second resolver after that to do your normal action, then potentially even a third that could send the email that someone has hit the limit.