How to map lambda error to API Gateway error response with Serverless Framework
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Serverless Framework provides an easy way to deploy aws serverless applications. In this article, I'll show you how to build a simple REST API handling error from Lambda Function.
Prerequisite
- AWS account
- Node.js
- AWS CLI (configured).
Sample Repository and Usage
git clone git@github.com:cm-wada-yusuke/sls-lambda-error-api-integration-sample.git
cd sls-lambda-error-api-integration-sample
yarn install
yarn deploy # sls deploy
Check 1: Create a REST Resource for handling error
I updated serverless.yml as shown below.
service: api-response-codes
provider:
name: aws
runtime: nodejs12.x
plugins:
- serverless-offline
functions:
hello:
handler: handler.hello
events:
- http:
method: get
path: whatever
integration: lambda
response:
headers:
Content-Type: "'application/json'"
template: $input.path('$')
statusCodes:
200:
pattern: "" # Default response method
template: $input.path("$.body")
404:
pattern: '.*"statusCode":404,.*' # JSON response
template: $util.parseJson($input.json('$.errorMessage')) # JSON return object
headers:
Content-Type: "'application/json'"
Highlighted object deploys API Gateway Integration Response:
Check 2: Create a Lambda Function that responds error status
Lambda code is simple, but note an error mapping with the API Gateway:
- Our API Gateway's
Lambda Error Regexruns a check when throwing an exception in Lambda Function. It does not run on a regular response. - Our Lambda Function packs the exception into an object called
errorMessageby herself.
See documentation for more details.
Handle Lambda errors in API Gateway - Amazon API Gateway
I've written a Lambda Function to cause errors on purpose.
exports.hello = async (event, context) => {
const error = true;
if (error) {
throw new Error(JSON.stringify({
statusCode: 404,
message: "order not found"
}));
} else {
return {
body: 'Hello from Lambda!',
};
}
};
throw new Error(JSON.stringify({statusCode: 404,message:"order not found"})); - this error will be packed to another object:
{
"errorMessage": "{\"statusCode\":404,\"message\":\"order not found\"}",
"errorType": "somestring",
"stackTrace": [
"somestring",
...
]
}
In the API Gateway, errorMessage is checked with regex pattern -- .*"statusCode":404,.* in this time. Finally, the API call failed to get and respond 404 code and parsed the error message.
Conclusion
In this article, I showed you how to create API Gateway integration response handling Lambda Function error.
![[ServerlessFramework] アクセスキーによるデプロイの運用方法を考えてみた](https://images.ctfassets.net/ct0aopd36mqt/wp-thumbnail-4fe785b14e998b3c159119acfb76c6d7/827db674ed6e7c651836f5c6bef1323a/serverless-framework-icon.png){kind=icon}
