问题
I have a DynamoDB connected to step functions and I am building a UI to display changes. I connected the DB to an AppSync instance and have tried using subscriptions through AppSync, but it seems they only observe mutations within the current AppSync.
How can I subscribe to the data source changes directly?
回答1:
You are correct. Currently, AppSync Subscriptions are only triggered from GraphQL Mutations. If there are changes made to the DynamoDB from a source other than AppSync, subscriptions will not trigger.
If you want to track all changes being made to DynamoDB table and publish them using AppSync, you can do the following:
1) Setup a DynamoDB stream to capture changes and feed the changes to AWS Lambda
https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Streams.html https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Streams.Lambda.html
2) Setup an AppSync mutation with a Local (no datasource) resolver. You can use this to publish messages to subscribers without writing to a datasource.
https://docs.aws.amazon.com/appsync/latest/devguide/tutorial-local-resolvers.html
3) Make the DynamoDB Stream Lambda function (setup in step 1) call the AWS AppSync mutation (setup in step 2).
This will enable publishing ALL changes made to a DynamoDB table to AppSync subscribers, regardless of where the change came from.
来源：https://stackoverflow.com/questions/51659099/how-do-i-subscribe-directly-to-my-aws-appsync-data-source