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 …
How to model one-to-many relationships with AppSync and DynamoDB Read More »
TL;DR To make an AppSync DynamoDB resolver throw exceptions on conditional check errors, we need to check $context.error in the response mapping template ourselves. Like this: #if ( $ctx.error ) #if ( $ctx.error.type.equals(“DynamoDB:ConditionalCheckFailedException”) ) $util.error(“your error message”) #else $util.error($ctx.error.message, $ctx.error.type) #end #end $utils.toJson($context.result) And now, the longer version. The problem AppSync lets us perform DynamoDB …
AppSync: how to error on DynamoDB conditional check failures Read More »
Last week, someone asked me at the AWS User Group in The Hague “Is caching still relevant for serverless applications?” The assumption there is that Lambda auto-scales by traffic, so do we still need to worry about caching? And if so, where and how do we implement caching? So let’s break it down. Caching is …
All you need to know about caching for serverless applications Read More »
Update 17/09/2019: based on feedback, I added a few more alternatives that do not require you to deploy additional Lambda functions to the e2e-test stage. Scroll to the end to find out more. Being event-driven is a key characteristic of a serverless architecture. Often our Lambda functions would publish events to SNS topics or Kinesis …
How to include SNS and Kinesis in your e2e tests Read More »
Recently, I have been helping a client implement an event-sourced system. In the process, I put together a very simple demo app to illustrate how one could build such a system using Lambda and DynamoDB. The source code is available on GitHub here. Before you go ahead and read all about the demo app, I …
A simple event-sourcing example with snapshots using Lambda and DynamoDB Read More »
A while back I wrote about using DynamoDB TTL to implement ad-hoc scheduling. It generated some healthy debate and a few of you have mentioned alternatives including using Step Functions. So let’s take a look at some of these alternatives, starting with the simplest – using a cron job. We will assess this approach using the …
Using CloudWatch and Lambda to implement ad-hoc scheduling Read More »
Update 15/03/2019: Thanks to Zac Charles who pointed me to this new page in the DynamoDB docs. It explains how the OnDemand capacity mode works. Turns out you DON’T need to pre-warm a table. You just need to create the table with the desired peak throughput (Provisioned), and then change it to OnDemand. After you change the table to OnDemand …
Understanding the scaling behaviour of DynamoDB OnDemand tables Read More »
CloudWatch Events let you easily create cron jobs with Lambda. However, it’s not designed for running lots of ad-hoc tasks, each to be executed once, at a specific time. The default limit on CloudWatch Events is a lowly 100 rules per region per account. It’s a soft limit, so it’s possible to request a limit …
In the last post, we look at how you can implement pub-sub with AWS Lambda. We compared several event sources you can use, SNS, Kinesis streams and DynamoDB streams, and the tradeoffs available to you. Let’s look at another messaging pattern today, push-pull, which is often referred to as fan-out/fan-in. It’s really two separate patterns …
AWS offers a wealth of options for implementing messaging patterns such as pub-sub with Lambda, let’s compare and contrast some of these options. The pub-sub pattern Publish-Subscribe (often shortened to pub-sub) is a messaging pattern where publishers and subscribers are decoupled through an intermediary broker (ZeroMQ, RabbitMQ, SNS, etc.). SNS + Lambda In the AWS ecosystem, the obvious …
What is the best event source for doing pub-sub with AWS Lambda? Read More »
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