With a new support for Java; Lambda has become a very good candidate for implementing many of the microservices (and providing a RESTful interface via API Gateway).
Initiall the documentation on how to connect them was lacking (both docs and functionality has improved recently; e.g. enabling CORS no longer takes 20+ min). A key point is to implement the RequestHandler interface as described in the official docs; note that you will need to create custom Request and Response objects; using generic ones (e.g. String) would thrown an exception.

This is a seed application.

Lambda

Building

First you'll need to package your program. You can do that by executing:

• sbt assembly

(note the output path; you'll need to grab that jar later)

Setup

Go to console; and create a new lambda function.

• runtime: Java 8
• upload a .ZIP file: jar produced by the sbt assembly; e.g. target/scala-2.11/aws-lambda-scala-api-gateway-assembly-1.0.jar
• handler: specify a full quantified class name (no need to included the method): e.g.: org.activeintel.lambda.seed.post.Handler (for get use handler from another corresponding package ...seed.get.Handler)
• role: create basic execution role (if you haven't already)

After your lambda function has been created; make sure that it run by doing a test from AWS console.

Integration of Lambda and API Gateway

From API Gateway console; select your function (note that doing this from lambda console API Endpoints will result in exception; since some of the permissions don't get set up properly)

POST

For testing, make sure to include corresponding bodies through API Gateway, and Lambda e.g. pass the following in the Request Body:

{ 
    "firstName": "John",
     "lastName": "Doe" 
}  

GET

When creating resource; you'll need to encode part of the path which is used as argument; e.g. {messageID}

You'll also need to add mapping rules to get the argument under Integration Request

In the mapping section; select mapping template and add e.g.:

{
    "messageID" : "$input.params('messageID')"
}

for more information see: http://docs.aws.amazon.com/apigateway/latest/developerguide/api-gateway-mapping-template-reference.html

Enable CORS for a Method in API Gateway

You'll probably need to allow cross-domain call; to do that please follow: http://docs.aws.amazon.com/apigateway/latest/developerguide/how-to-cors.html

OLD

NOTE: the documentation is a little confusing; see this post (by Stefano@AWS) for clarifications: https://forums.aws.amazon.com/thread.jspa?messageID=644489&

Nice Folks at AWS have listened; and now there is a button that does all of the steps necessary to enable CORS.

Give Lambda Permissions to AWS Resources

Simplest way is to configure through IAM/Roles/Create Role Policy

p.s. you can look up the role name of your lambda see Lambda/Functions/YOUR-Function/Configuration/Role

See Also

http://docs.aws.amazon.com/lambda/latest/dg/java-handler-io-type-pojo.html

Keywords:

java lambda scala aws amazon api gateway rest restful

Exceptions

XMLHttpRequest cannot load https://ddd.execute-api.us-east-1.amazonaws.com/test/data. Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://ddd.s3-website-us-east-1.amazonaws.com' is therefore not allowed access. The response had HTTP status code 403.

{
"message": "Missing Authentication Token"
}

                Execution log for request test-request
Sun Oct 04 04:40:30 UTC 2015 : Starting execution for request: test-invoke-request
Sun Oct 04 04:40:30 UTC 2015 : API Key: test-invoke-api-key
Sun Oct 04 04:40:30 UTC 2015 : Method request path: {}
Sun Oct 04 04:40:30 UTC 2015 : Method request query string: {}
Sun Oct 04 04:40:30 UTC 2015 : Method request headers: {}
Sun Oct 04 04:40:30 UTC 2015 : Method request body before transformations: null
Sun Oct 04 04:40:30 UTC 2015 : Endpoint request URI: 
https://lambda.us-east-1.amazonaws.com/2015-03-31/functions/arn:aws:lambda:us-east-1:function:testFunction/invocations
Sun Oct 04 04:40:30 UTC 2015 : Endpoint request headers: 
{Authorization=*******************************************************************************************************************************************************************************************************************************, 
X-Amz-Date=20151004T044030Z, X-Amz-Source-Arn=arn:aws:execute-api:us-east-1:/null/POST/testMessage, 
Accept=application/json, User-Agent=AmazonAPIGateway, Host=lambda.us-east-1.amazonaws.com}
Sun Oct 04 04:40:30 UTC 2015 : Endpoint request body after transformations: 
Sun Oct 04 04:40:30 UTC 2015 : Execution failed due to configuration error: Invalid permissions on Lambda function

{
"Type": "User",
"message": "Could not parse request body into json."
}rialize instance of java.lang.String out of START_OBJECT token\n at [Source: lambdainternal.util.NativeMemoryAsInputStream@3224f60b; line: 1, column: 1]",
"errorType": "com.fasterxml.jackson.databind.JsonMappingException",
"stackTrace": [
"com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:148)",
"com.fasterxml.jackson.databind.DeserializationContext.mappingException(DeserializationContext.java:835)",
"com.fasterxml.jackson.databind.deser.std.StringDeserializer.deserialize(StringDeserializer.java:59)",
"com.fasterxml.jackson.databind.deser.std.StringDeserializer.deserialize(StringDeserializer.java:12)",
"com.fasterxml.jackson.databind.ObjectReader._bindAndClose(ObjectReader.java:1441)",
"com.fasterxml.jackson.databind.ObjectReader.readValue(ObjectReader.java:1047)"
]
}
}
}n."
}

{
"errorMessage": "An error occurred during JSON parsing",
"errorType": "java.lang.RuntimeException",
"stackTrace": [],
"cause": {
"errorMessage": "com.fasterxml.jackson.databind.JsonMappingException: Can not deserialize instance of java.lang.String out of START_OBJECT token\n at [Source: lambdainternal.util.NativeMemoryAsInputStream@72b6cbcc; line: 1, column: 1]",
"errorType": "java.io.UncheckedIOException",
"stackTrace": [],
"cause": {
"errorMessage": "Can not deserialize instance of java.lang.String out of START_OBJECT token\n at [Source: lambdainternal.util.NativeMemoryAsInputStream@72b6cbcc; line: 1, column: 1]",
"errorType": "com.fasterxml.jackson.databind.JsonMappingException",
"stackTrace": [
"com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:148)",
"com.fasterxml.jackson.databind.DeserializationContext.mappingException(DeserializationContext.java:835)",
"com.fasterxml.jackson.databind.deser.std.StringDeserializer.deserialize(StringDeserializer.java:59)",
"com.fasterxml.jackson.databind.deser.std.StringDeserializer.deserialize(StringDeserializer.java:12)",
"com.fasterxml.jackson.databind.ObjectReader._bindAndClose(ObjectReader.java:1441)",
"com.fasterxml.jackson.databind.ObjectReader.readValue(ObjectReader.java:1047)"
]
}
}
}rialize instance of java.lang.String out of START_OBJECT token\n at [Source: lambdainternal.util.NativeMemoryAsInputStream@3224f60b; line: 1, column: 1]",
"errorType": "com.fasterxml.jackson.databind.JsonMappingException",
"stackTrace": [
"com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:148)",
"com.fasterxml.jackson.databind.DeserializationContext.mappingException(DeserializationContext.java:835)",
"com.fasterxml.jackson.databind.deser.std.StringDeserializer.deserialize(StringDeserializer.java:59)",
"com.fasterxml.jackson.databind.deser.std.StringDeserializer.deserialize(StringDeserializer.java:12)",
"com.fasterxml.jackson.databind.ObjectReader._bindAndClose(ObjectReader.java:1441)",
"com.fasterxml.jackson.databind.ObjectReader.readValue(ObjectReader.java:1047)"
]
}
}
}n."
}

{
"errorMessage": "An error occurred during JSON parsing",
"errorType": "java.lang.RuntimeException",
"stackTrace": [],
"cause": {
"errorMessage": "com.fasterxml.jackson.databind.JsonMappingException: Can not deserialize instance of java.lang.String out of START_OBJECT token\n at [Source: lambdainternal.util.NativeMemoryAsInputStream@7494e528; line: 1, column: 1]",
"errorType": "java.io.UncheckedIOException",
"stackTrace": [],
"cause": {
"errorMessage": "Can not deserialize instance of java.lang.String out of START_OBJECT token\n at [Source: lambdainternal.util.NativeMemoryAsInputStream@7494e528; line: 1, column: 1]",
"errorType": "com.fasterxml.jackson.databind.JsonMappingException",
"stackTrace": [
"com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:148)",
"com.fasterxml.jackson.databind.DeserializationContext.mappingException(DeserializationContext.java:835)",
"com.fasterxml.jackson.databind.deser.std.StringDeserializer.deserialize(StringDeserializer.java:59)",
"com.fasterxml.jackson.databind.deser.std.StringDeserializer.deserialize(StringDeserializer.java:12)",
"com.fasterxml.jackson.databind.ObjectReader._bindAndClose(ObjectReader.java:1441)",
"com.fasterxml.jackson.databind.ObjectReader.readValue(ObjectReader.java:1047)"
]
}
}
}

Integration Request Exception

Fix: Make sure to follow Integration Request instructions

The provided key element does not match the schema (Service: AmazonDynamoDBv2; Status Code: 400; Error Code: ValidationException; Request ID: ): com.amazonaws.AmazonServiceException com.amazonaws.AmazonServiceException: The provided key element does not match the schema (Service: AmazonDynamoDBv2; Status Code: 400; Error Code: ValidationException; Request ID: ) at com.amazonaws.http.AmazonHttpClient.handleErrorResponse(AmazonHttpClient.java:1275) at com.amazonaws.http.AmazonHttpClient.executeOneRequest(AmazonHttpClient.java:873) at com.amazonaws.http.AmazonHttpClient.executeHelper(AmazonHttpClient.java:576) at com.amazonaws.http.AmazonHttpClient.doExecute(AmazonHttpClient.java:362) at com.amazonaws.http.AmazonHttpClient.executeWithTimer(AmazonHttpClient.java:328) at com.amazonaws.http.AmazonHttpClient.execute(AmazonHttpClient.java:307) at com.amazonaws.services.dynamodbv2.AmazonDynamoDBClient.invoke(AmazonDynamoDBClient.java:1776) at com.amazonaws.services.dynamodbv2.AmazonDynamoDBClient.getItem(AmazonDynamoDBClient.java:1145) at com.amazonaws.services.dynamodbv2.document.internal.GetItemImpl.doLoadItem(GetItemImpl.java:77) at com.amazonaws.services.dynamodbv2.document.internal.GetItemImpl.getItemOutcome(GetItemImpl.java:40) at com.amazonaws.services.dynamodbv2.document.internal.GetItemImpl.getItemOutcome(GetItemImpl.java:99) at com.amazonaws.services.dynamodbv2.document.internal.GetItemImpl.getItem(GetItemImpl.java:111) at com.amazonaws.services.dynamodbv2.document.Table.getItem(Table.java:610)