Call Lambda function with proxy integration from another Lambda function without passing through the Api Gateway

Question

I have deployed two lambda functions with proxy integration on AWS. Each of them is referenced from its corresponding API Gateway entry using the proxy wildcard:

The idea is to have two APIs, one per function, let's suppose this is what they offer:

API 1 -> Lambda 1 -> ms-user

GET /users GET /users/{userId} POST /user

API 2 -> Lambda 2 -> ms-departments

GET /departments POST /departments

Certain operations from Lambda 2 have to call Lambda 1, e.g: GET /departments needs to get user information, GET /users/{userId}.

I could make Lambda 2 invoke the API of Lambda 1, but I am wondering is there is a way to call that lambda directly with the AWS Java SDK without passing through the Gateway again. In that case how can I specify the endpoint of the target Lambda?

API 2 -> Lambda 2 -> Lambda 1

instead of

API 2 -> Lambda 2 -> API 1 -> Lambda 1

codependent · Accepted Answer · 2019-06-28 12:48:05Z

The key to achieve this is to pass a request containing certain expected fields, e.g:

{ "path": "/users/1234D", "httpMethod": "GET", "headers": null, "multiValueHeaders": { "Host": [ "xxxx.execute-api.eu-west-1.amazonaws.com" ] } }

The Java/Kotlin code would be:

 val region = Regions.fromName("eu-west-1") val builder = AWSLambdaClientBuilder.standard().withRegion(region) val client = builder.build() val req = InvokeRequest().withFunctionName("ms-user") .withPayload("""{ "path": "/users/${req.userId}", "httpMethod": "GET", "headers": null, "multiValueHeaders": { "Host": [ "xxx.execute-api.eu-west-3.amazonaws.com" ] } }""") val result = client.invoke(req)

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