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Read this on the main serverless docs site
API Gateway
To create HTTP endpoints as Event sources for your AWS Lambda Functions, use the Serverless Framework's easy AWS API Gateway Events syntax.
There are two ways you can configure your HTTP endpoints to integrate with your AWS Lambda Functions:
- lambda-proxy (Recommended)
- lambda
The difference between these is lambda-proxy automatically passes the content of the HTTP request into your AWS Lambda function (headers, body, etc.) and allows you to configure your response (headers, status code, body) in the code of your AWS Lambda Function. Whereas, the lambda method makes you explicitly define headers, status codes, and more in the configuration of each API Gateway Endpoint (not in code). We highly recommend using the lambda-proxy method if it supports your use-case, since the lambda method is highly tedious.
By default, the Framework uses the lambda-proxy method (i.e., everything is passed into your Lambda), and nothing is required by you to enable it.
Lambda Proxy Integration
Simple HTTP Endpoint
This setup specifies that the hello function should be run when someone accesses the API gateway at hello via
a GET request.
Here's an example:
# serverless.yml
functions:
index:
handler: handler.hello
events:
- http: GET hello
// handler.js
'use strict';
module.exports.hello = function(event, context, callback) {
console.log(event); // Contains incoming request data (e.g., query params, headers and more)
const response = {
statusCode: 200,
headers: {
"x-custom-header" : "My Header Value"
},
body: JSON.stringify({ "message": "Hello World!" })
};
callback(null, response);
};
Note: When the body is a JSON-Document, you must parse it yourself:
JSON.parse(event.body);
HTTP Endpoint with Extended Options
Here we've defined an POST endpoint for the path posts/create.
# serverless.yml
functions:
create:
handler: posts.create
events:
- http:
path: posts/create
method: post
Enabling CORS
To set CORS configurations for your HTTP endpoints, simply modify your event configurations as follows:
# serverless.yml
functions:
hello:
handler: handler.hello
events:
- http:
path: hello
method: get
cors: true
Setting cors to true assumes a default configuration which is equivalent to:
functions:
hello:
handler: handler.hello
events:
- http:
path: hello
method: get
cors:
origins:
- '*'
headers:
- Content-Type
- X-Amz-Date
- Authorization
- X-Api-Key
- X-Amz-Security-Token
allowCredentials: false
Configuring the cors property sets Access-Control-Allow-Origin, Access-Control-Allow-Headers, Access-Control-Allow-Methods,Access-Control-Allow-Credentials headers in the CORS preflight response.
If you want to use CORS with the lambda-proxy integration, remember to include the Access-Control-Allow-* headers in your headers object, like this:
// handler.js
'use strict';
module.exports.hello = function(event, context, callback) {
const response = {
statusCode: 200,
headers: {
"Access-Control-Allow-Origin" : "*", // Required for CORS support to work
"Access-Control-Allow-Credentials" : true // Required for cookies, authorization headers with HTTPS
},
body: JSON.stringify({ "message": "Hello World!" })
};
callback(null, response);
};
HTTP Endpoints with Custom Authorizers
Custom Authorizers allow you to run an AWS Lambda Function before your targeted AWS Lambda Function. This is useful for Microservice Architectures or when you simply want to do some Authorization before running your business logic.
You can enable Custom Authorizers for your HTTP endpoint by setting the Authorizer in your http event to another function
in the same service, as shown in the following example:
functions:
create:
handler: posts.create
events:
- http:
path: posts/create
method: post
authorizer: authorizerFunc
authorizerFunc:
handler: handler.authorizerFunc
Or, if you want to configure the Authorizer with more options, you can turn the authorizer property into an object as
shown in the following example:
functions:
create:
handler: posts.create
events:
- http:
path: posts/create
method: post
authorizer:
name: authorizerFunc
resultTtlInSeconds: 0
identitySource: method.request.header.Authorization
identityValidationExpression: someRegex
authorizerFunc:
handler: handler.authorizerFunc
If the Authorizer function does not exist in your service but exists in AWS, you can provide the ARN of the Lambda function instead of the function name, as shown in the following example:
functions:
create:
handler: posts.create
events:
- http:
path: posts/create
method: post
authorizer: xxx:xxx:Lambda-Name
Or, if you want to configure the Authorizer with more options, you can turn the authorizer property into an object as
shown in the following example:
functions:
create:
handler: posts.create
events:
- http:
path: posts/create
method: post
authorizer:
arn: xxx:xxx:Lambda-Name
resultTtlInSeconds: 0
identitySource: method.request.header.Authorization
identityValidationExpression: someRegex
You can also configure an existing Cognito User Pool as the authorizer, as shown in the following example:
functions:
create:
handler: posts.create
events:
- http:
path: posts/create
method: post
authorizer:
arn: arn:aws:cognito-idp:us-east-1:xxx:userpool/us-east-1_ZZZ
By default the sub claim will be exposed in events.cognitoPoolClaims, you can add extra claims like so:
functions:
create:
handler: posts.create
events:
- http:
path: posts/create
method: post
integration: lambda
authorizer:
arn: arn:aws:cognito-idp:us-east-1:xxx:userpool/us-east-1_ZZZ
claims:
- email
- nickname
Note: Since claims must be explicitly listed to be exposed, you must use integration: lambda integration type to access any claims.
Catching Exceptions In Your Lambda Function
In case an exception is thrown in your lambda function AWS will send an error message with Process exited before completing request. This will be caught by the regular expression for the 500 HTTP status and the 500 status will be returned.
Setting API keys for your Rest API
Note: Due to a CloudFormation restriction you need to wire up API Keys and usage plans manually in the AWS console.
You can specify a list of API keys to be used by your service Rest API by adding an apiKeys array property to the
provider object in serverless.yml. You'll also need to explicitly specify which endpoints are private and require
one of the api keys to be included in the request by adding a private boolean property to the http event object you
want to set as private. API Keys are created globally, so if you want to deploy your service to different stages make sure
your API key contains a stage variable as defined below.
Here's an example configuration for setting API keys for your service Rest API:
service: my-service
provider:
name: aws
apiKeys:
- myFirstKey
- ${opt:stage}-myFirstKey
- ${env:MY_API_KEY} # you can hide it in a serverless variable
functions:
hello:
events:
- http:
path: user/create
method: get
private: true
Please note that those are the API keys names, not the actual values. Once you deploy your service, the value of those API keys will be auto generated by AWS and printed on the screen for you to use.
Clients connecting to this Rest API will then need to set any of these API keys values in the x-api-key header of their request. This is only necessary for functions where the private property is set to true.
Lambda Integration
This method is more complicated and involves a lot more configuration of the http event syntax.
Request Parameters
To pass optional and required parameters to your functions, so you can use them in API Gateway tests and SDK generation, marking them as true will make them required, false will make them optional.
functions:
create:
handler: posts.create
events:
- http:
path: posts/create
method: post
integration: lambda
request:
parameters:
querystrings:
url: true
headers:
foo: false
bar: true
paths:
bar: false
In order for path variables to work, API Gateway also needs them in the method path itself, like so:
functions:
create:
handler: posts.post_detail
events:
- http:
path: posts/{id}
method: get
integration: lambda
request:
parameters:
paths:
id: true
Request templates
Default Request Templates
Serverless ships with the following default request templates you can use out of the box:
application/jsonapplication/x-www-form-urlencoded
Both templates give you access to the following properties you can access with the help of the event object:
- body
- method
- principalId
- stage
- headers
- query
- path
- identity
- stageVariables
Custom Request Templates
However you can define and use your own request templates as follows (you can even overwrite the default request templates by defining a new request template for an existing content type):
functions:
create:
handler: posts.create
events:
- http:
method: get
path: whatever
integration: lambda
request:
template:
text/xhtml: '{ "stage" : "$context.stage" }'
application/json: '{ "httpMethod" : "$context.httpMethod" }'
Note: The templates are defined as plain text here. However you can also reference an external file with the help of the ${file(templatefile)} syntax.
Note 2: In .yml, strings containing :, {, }, [, ], ,, &, *, #, ?, |, -, <, >, =, !, %, @, ` must be quoted.
If you want to map querystrings to the event object, you can use the $input.params('hub.challenge') syntax from API Gateway, as follows:
functions:
create:
handler: posts.create
events:
- http:
method: get
path: whatever
integration: lambda
request:
template:
application/json: '{ "foo" : "$input.params(''bar'')" }'
Note: Notice when using single-quoted strings, any single quote ' inside its contents must be doubled ('') to escape it.
You can then access the query string https://example.com/dev/whatever?bar=123 by event.foo in the lambda function.
If you want to spread a string into multiple lines, you can use the > or | syntax, but the following strings have to be all indented with the same amount, read more about > syntax.
Pass Through Behavior
API Gateway provides multiple ways to handle requests where the Content-Type header does not match any of the specified mapping templates. When this happens, the request payload will either be passed through the integration request without transformation or rejected with a 415 - Unsupported Media Type, depending on the configuration.
You can define this behavior as follows (if not specified, a value of NEVER will be used):
functions:
create:
handler: posts.create
events:
- http:
method: get
path: whatever
integration: lambda
request:
passThrough: NEVER
There are 3 available options:
| Value | Passed Through When | Rejected When |
|---|---|---|
| NEVER | Never | No templates defined or Content-Type does not match a defined template |
| WHEN_NO_MATCH | Content-Type does not match defined template | Never |
| WHEN_NO_TEMPLATES | No templates were defined | One or more templates defined, but Content-Type does not match |
See the api gateway documentation for detailed descriptions of these options.
Notes:
- A missing/empty request Content-Type is considered to be the API Gateway default (
application/json) - API Gateway docs refer to "WHEN_NO_TEMPLATE" (singular), but this will fail during creation as the actual value should be "WHEN_NO_TEMPLATES" (plural)
Responses
Serverless lets you setup custom headers and a response template for your http event.
Custom Response Headers
Here's an example which shows you how you can setup a custom response header:
functions:
create:
handler: posts.create
events:
- http:
method: get
path: whatever
integration: lambda
response:
headers:
Content-Type: integration.response.header.Content-Type
Cache-Control: "'max-age=120'"
Note: You're able to use the integration response variables
for your header values. Headers are passed to API Gateway exactly like you define them. Passing the Cache-Control header
as "'max-age=120'" means API Gateway will receive the value as 'max-age=120' (enclosed with single quotes).
Custom Response Templates
Sometimes you'll want to define a custom response template API Gateway should use to transform your lambdas output. Here's an example which will transform the return value of your lambda so that the browser renders it as HTML:
functions:
create:
handler: posts.create
events:
- http:
method: get
path: whatever
integration: lambda
response:
headers:
Content-Type: "'text/html'"
template: $input.path('$')
Note: The template is defined as plain text here. However you can also reference an external file with the help of
the ${file(templatefile)} syntax.
Status codes
Serverless ships with default status codes you can use to e.g. signal that a resource could not be found (404) or that the user is not authorized to perform the action (401). Those status codes are regex definitions that will be added to your API Gateway configuration.
Available Status Codes
| Status Code | Meaning |
|---|---|
| 400 | Bad Request |
| 401 | Unauthorized |
| 403 | Forbidden |
| 404 | Not Found |
| 422 | Unprocessable Entity |
| 500 | Internal Server Error |
| 502 | Bad Gateway |
| 504 | Gateway Timeout |
Using Status Codes
To return a given status code you simply need to add square brackets with the status code of your choice to your
returned message like this: [401] You are not authorized to access this resource!.
Here's an example which shows you how you can raise a 404 HTTP status from within your lambda function.
module.exports.hello = (event, context, callback) => {
callback(new Error('[404] Not found'));
}
Custom Status Codes
You can override the defaults status codes supplied by Serverless. You can use this to change the default status code, add/remove status codes, or change the templates and headers used for each status code. Use the pattern key to change the selection process that dictates what code is returned.
If you specify a status code with a pattern of '' that will become the default response code. See below on how to change the default to 201 for post requests.
If you omit any default status code. A standard default 200 status code will be generated for you.
functions:
create:
handler: posts.create
events:
- http:
method: post
path: whatever
integration: lambda
response:
headers:
Content-Type: "'text/html'"
template: $input.path('$')
statusCodes:
201:
pattern: '' # Default response method
409:
pattern: '.*"statusCode":409,.*' # JSON response
template: $input.path("$.errorMessage") # JSON return object
headers:
Content-Type: "'application/json+hal'"
You can also create varying response templates for each code and content type by creating an object with the key as the content type
functions:
create:
handler: posts.create
events:
- http:
method: post
path: whatever
integration: lambda
response:
headers:
Content-Type: "'text/html'"
template: $input.path('$')
statusCodes:
201:
pattern: '' # Default response method
409:
pattern: '.*"statusCode":409,.*' # JSON response
template:
application/json: $input.path("$.errorMessage") # JSON return object
application/xml: $input.path("$.body.errorMessage") # XML return object
headers:
Content-Type: "'application/json+hal'"
Setting an HTTP Proxy on API Gateway
To set up an HTTP proxy, you'll need two CloudFormation templates, one for the endpoint (known as resource in CF), and
one for method. These two templates will work together to construct your proxy. So if you want to set your-app.com/serverless as a proxy for serverless.com, you'll need the following two templates in your serverless.yml:
service: service-name
provider: aws
functions:
...
resources:
Resources:
ProxyResource:
Type: AWS::ApiGateway::Resource
Properties:
ParentId:
Fn::GetAtt:
- ApiGatewayRestApi # our default Rest API logical ID
- RootResourceId
PathPart: serverless # the endpoint in your API that is set as proxy
RestApiId:
Ref: ApiGatewayRestApi
ProxyMethod:
Type: AWS::ApiGateway::Method
Properties:
ResourceId:
Ref: ProxyResource
RestApiId:
Ref: ApiGatewayRestApi
HttpMethod: GET # the method of your proxy. Is it GET or POST or ... ?
MethodResponses:
- StatusCode: 200
Integration:
IntegrationHttpMethod: POST
Type: HTTP
Uri: http://serverless.com # the URL you want to set a proxy to
IntegrationResponses:
- StatusCode: 200
There's a lot going on in these two templates, but all you need to know to set up a simple proxy is setting the method & endpoint of your proxy, and the URI you want to set a proxy to.
Now that you have these two CloudFormation templates defined in your serverless.yml file, you can simply run
serverless deploy and that will deploy these custom resources for you along with your service and set up a proxy on your Rest API.