Routes and Events

About

For the 5.31.0 version of Webiny we have refactored our handler package (@webiny/handler) to use fastify. Fastify has quite extensive documentation, so feel free to check it out if you need to modify our default behavior.

Fastify enables us to:

• add the possibility to add new routes and event handling
• consistent request and reply (formerly response in our system) methods throughout the system
• a lot of request lifecycle events for users to hook into
• implement some other cloud service, at some point, more easily

The new @webiny/handler package does not differentiate between incoming Lambda requests, that is left to the @webiny/handler-aws package, which exports a few handler possibilities:

• API Gateway handler
• Raw handler
• EventBridge handler
• SQS handler
• S3 handler
• DynamoDB handler

Why All the Different Handlers?

Well, the API Gateway handler and the Raw handler are actually only ones that are really required. The others are there to help with typings and some other checks.

API Gateway Handler

This handler uses @fastify/aws-lambda in the background to handle API Gateway events. It transforms APIGatewayEvent into the request which fastify understands, and it is then used throughout the system.

For this handler to work it requires at least one RoutePlugin to be initialized. It always returns LambdaResponse defined in the @fastify/aws-lambda package.

Raw Handler

This handler uses a nice fastify feature that allows you to run any route you have previously defined. So basically, on initialization of the handler we add some dummy route (something like webiny-raw-event) and then run it via the .inject() method on fastify instance. This is the same procedure being used in the @fastify/aws-lambda package. The difference is that our Raw handler can return either APIGatewayProxyResult or what ever is directly sent from the EventPlugin.

For this handler to work it requires exactly one EventPlugin to be defined. If more, or none, are defined, an error will be thrown.

S3 Handler

This handler works as the Raw handler does, only it expects S3EventHandler plugin.

EventBridge Handler

This handler works as the Raw handler does, only it expects EventBridgeEventHandler plugin.

SQS Handler

This handler works as the Raw handler does, only it expects SQSEventHandler plugin.

DynamoDB Handler

This handler works as the Raw handler does, only it expects DynamoDBEventHandler plugin.

Difference BetweencreateHandlerandcreateEventHandler

There are two methods of defining the event handling:

• createHandler
• createEventHandler

What Is thecreateHandlerMethod?

This method creates the base of Webiny system. It will initialize fastify, context and everything which is defined by plugins that were passed on.

We have built-in methods for different types of events:

• API Gateway

createApiGatewayHandler if imported from @webiny/handler-aws or createHandler if imported from @webiny/handler-aws/gateway

• Raw handler

createRawHandler if imported from @webiny/handler-aws or createHandler if imported from @webiny/handler-aws/raw

• EventBridge handler

createEventBridgeHandler if imported from @webiny/handler-aws or createHandler if imported from @webiny/handler-aws/eventBridge

• SQS handler

createSQSHandler if imported from @webiny/handler-aws or createHandler if imported from @webiny/handler-aws/sqs

• S3 handler

createS3Handler if imported from @webiny/handler-aws or createHandler if imported from @webiny/handler-aws/s3

• DynamoDB handler

createDynamoDBHandler if imported from @webiny/handler-aws or createHandler if imported from @webiny/handler-aws/dynamodb

Depending on your need, you can import which ever is most suitable. You can import methods from the root of the @webiny/handler-aws package.

What Is thecreateEventHandlerMethod?

This method creates the handler for the received event. At this point whole Webiny system is ready - all passed plugins are applied, security checks are done, etc…

We have built-in methods for different types of events:

• API Gateway

createApiGatewayRoute if imported from @webiny/handler-aws or createRoute if imported from @webiny/handler-aws/gateway

• Raw handler

createRawEventHandler if imported from @webiny/handler-aws or createEventHandler if imported from @webiny/handler-aws/raw

• EventBridge handler

createEventBridgeEventHandler if imported from @webiny/handler-aws or createEventHandler if imported from @webiny/handler-aws/eventBridge

• SQS handler

createSQSEventHandler if imported from @webiny/handler-aws or createEventHandler if imported from @webiny/handler-aws/sqs

• S3 handler

createS3EventHandler if imported from @webiny/handler-aws or createEventHandler if imported from @webiny/handler-aws/s3

• DynamoDB handler

createDynamoDBEventHandler if imported from @webiny/handler-aws or createEventHandler if imported from @webiny/handler-aws/dynamodb

Notice that all event handlers, except one for API Gateway, are named createEventHandler (or createSomethingEventHandler when importing from root).

The naming convention indicates the amount of event handlers you can define, so route is multiple whereas event is single.

Adding New Routes

Adding new routes is quite simple, but you need to add them via both Pulumi code and the RoutePlugin.

The Pulumi code goes into apps/api/webiny.application.ts. You must add the new route there, check out the example below, where we are adding a [POST]/webiny route.

Next thing you need to do is to add it into the apps/api/graphql/src/index.ts file via the RoutePlugin or createApiGatewayRoute method:

Adding Event Handler

The idea behind all our predefined event handlers is to handle events which are not of API Gateway Event type.

Yes, you can catch API Gateway event like this, but there is no point since we have a handler specifically designed for that. Of course, feel free to use whatever is available and can help you to achieve your goal.

Example

Let’s say you created a part of code which sends out an SQS message, and you want to have a Lambda which handles that message.

Good example would be if you want to run some calculation, asynchronously, from our GraphQL Lambda. You would insert an SQS Message and in turn it would trigger a Lambda which you have defined. That lambda should have code similar to this:

Event Handler Response

When handling an event, you can either return the reply object or something else, what ever you like. Basically, when you return the reply, a standard APIGatewayProxyResult is created out of the data, headers and cookies you sent. When you return anything else other than the reply, it is returned as the result of the handler, and the Lambda itself.

For example, you can send plain text or object to get the response of the Lambda without the need to parse the APIGatewayProxyResult.