87 lines
2.9 KiB
Markdown
87 lines
2.9 KiB
Markdown
---
|
|
tags:
|
|
- AWS
|
|
- aws-lambda
|
|
---
|
|
|
|
# AWS Lambda handler function
|
|
|
|
Every Lambda function begins the same way with a handler function. In NodeJS:
|
|
|
|
```js
|
|
module.exports.handler = function(event, context, callback){...}
|
|
```
|
|
|
|
The handler is the entry point for the Lambda. It is a function that Lambda can
|
|
call to start the execution of your code when an event triggers your Lambda
|
|
function.
|
|
|
|
You may put your whole code in the body of the handler, or you may call other
|
|
modules and keep the handler clean and focused on bootstrapping.
|
|
|
|
The `module.exports` part is just the standard way of exporting a module in
|
|
Node. `handler` is a property that is being exported.
|
|
|
|
You always have access to the parameters `event`, `context` and `callback`.
|
|
|
|
- `event`
|
|
- The triggering event of the Lambda function stored as an object. The
|
|
object's contents will be different depending on the trigger. It could be
|
|
any AWS service that serves a trigger (S3, DynamoDB, API Gateway etc).
|
|
- For example, if the triggering function is a request to API Gateway, the
|
|
`event` object will contain information about the HTTP request such as
|
|
headers, path, and the request body.
|
|
- `context`
|
|
- contains information about the runtime environment and the current execution
|
|
of the Lambda function. The context object provides properties and methods
|
|
that you can use to interact with the AWS Lambda service and the current
|
|
invocation.
|
|
- `callback`
|
|
- an optional parameter that represents a callback function provided by AWS
|
|
Lambda. The callback function allows you to signal the completion of your
|
|
Lambda function's execution and return a response or an error. The callback
|
|
function accepts two arguments: error and result. If the first argument is
|
|
not null, AWS Lambda treats it as an error, and the Lambda function
|
|
invocation fails. If the first argument is null, AWS Lambda treats the
|
|
second argument as the result and considers the invocation successful. Using
|
|
the callback function is more common in non-async handler functions. When
|
|
you use async functions, you can return a response or throw an error
|
|
directly, without using the callback function.
|
|
|
|
### Full example:
|
|
|
|
In JavaScript:
|
|
|
|
```js
|
|
module.exports.handler = async (event, context) => {
|
|
// Your logic to handle the incoming event
|
|
// For example, you can call other AWS services, process the event data, etc.
|
|
|
|
// Return a response
|
|
return {
|
|
statusCode: 200,
|
|
body: JSON.stringify({
|
|
message: "Your Lambda function has successfully executed!",
|
|
}),
|
|
};
|
|
};
|
|
```
|
|
|
|
In Python:
|
|
|
|
```py
|
|
import json
|
|
|
|
def handler(event, context):
|
|
# Your logic to handle the incoming event
|
|
# For example, you can call other AWS services, process the event data, etc.
|
|
|
|
# Return a response
|
|
response = {
|
|
'statusCode': 200,
|
|
'body': json.dumps({
|
|
'message': 'Your Lambda function has successfully executed!'
|
|
})
|
|
}
|
|
return response
|
|
```
|