AWS

How to work around CloudFormation circular dependencies

An interesting question came up on the AppSync Masterclass forum, and it highlights a common way you can get into CloudFormation circular dependencies. In the CloudFormation stack, there is an AppSync API, which uses a Cognito User Pool for authentication and authorization. When a user signs up, the app should fire an update on a …

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Group-based auth with AppSync Lambda authoriser

AWS AppSync added support for Lambda authorizers on 30th July 2021 and it made it much easier to implement group-based authorization with 3rd party identity services. Group-based auth with AppSync and Cognito I previously wrote about how you can secure multi-tenant applications with AppSync and Cognito. Where you can use custom attributes to capture the tenant …

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How to handle client errors gracefully with AppSync and Lambda

With API Gateway and Lambda, you can handle client errors gracefully by returning a 4xx response. module.exports.handler = async (event) => { // run validation logic return { statusCode: 400 } } This way, we can communicate clearly to the client that there’s a problem with its request. It also lets the Lambda invocation complete …

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How to manage Route53 hosted zones in a multi-account environment

An interesting question came up in a conversation today: “How should I manage the Route53 DNS records in a multi-account environment?” Suppose you have configured an AWS Organization with different accounts for dev, staging and production environments. And you have registered the root domain for your application in the master AWS account. When working with …

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Building a custom IAM system has made me appreciate AWS IAM even more

In the last post I discussed my preferred approach for modelling multi-tenant applications with AppSync and Cognito. This approach supports the common requirements in these applications, where there are a number of distinct roles within each tenant. This approach (and others like it) works great when the tenants are isolated. But what if they are …

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How to model one-to-many relationships with AppSync and DynamoDB

Thank you to Josh for asking this question on the AppSync Masterclass forum. His original question goes like this: Let’s say I want to add a one-to-many relationship from Profile to a new property called “Tag” (a complex object with “name” and “color” properties) so a user can define their own Tags. I would also like a …

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