Aws-sam-cli: Debugging SAM Local + Java in IntelliJ

[debuggins]

I am unable to hit breakpoints in IntelliJ (ver 14.1.7). I am using a Mac (ver. 10.13.3), SAM (ver. 0.2.8), and Docker (ver. 17.12.0-ce, build c97c6d6).

After starting sam local and then hitting the endpoint in Chrome, my console output is this:
```$ sam local start-api --debug-port 3000
2018/03/09 14:02:18 Connected to Docker 1.35
2018/03/09 14:02:18 Fetching lambci/lambda:java8 image for java8 runtime...
java8: Pulling from lambci/lambda
Digest: sha256:e1c82c7707c28f533480c76bb93a010f2279f699a0d7f8d3e9727082e0a81051
Status: Image is up to date for lambci/lambda:java8

Mounting com.amazonaws.lambda.hw.LambdaFunctionHandler::handleRequest (java8) at http://127.0.0.1:3000/ [GET]

You can now browse to the above endpoints to invoke your functions.
You do not need to restart/reload SAM CLI while working on your functions,
changes will be reflected instantly/automatically. You only need to restart
SAM CLI if you update your AWS SAM template.

2018/03/09 14:02:24 Invoking com.amazonaws.lambda.hw.LambdaFunctionHandler::handleRequest (java8)
2018/03/09 14:02:24 Decompressing /*/Hello World/target/hw-1.0.0.jar
2018/03/09 14:02:26 Mounting /private/var/folders/pr/zzhpj48x70l0gk6n1t11x74m0000gn/T/aws-sam-local-1520632944922829000 as /var/task:ro inside runtime container

It hangs after mounting and the page never loads.

My template.yaml looks like this:
```AWSTemplateFormatVersion : '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: 

Resources:
  GetFunction:
    Type: AWS::Serverless::Function
    Properties:
      FunctionName: handleRequest
      Handler: com.amazonaws.lambda.hw.LambdaFunctionHandler::handleRequest
      Runtime: java8
      CodeUri: target/hw-1.0.0.jar
      Timeout: 300
      Events:
        GetEvent:
          Type: Api
          Properties:
            Path: /
            Method: get

My LambdaFunctionHandler.java looks like this:
```package com.amazonaws.lambda.hw;

import com.amazonaws.services.lambda.runtime.Context;
import com.amazonaws.services.lambda.runtime.RequestHandler;
import org.json.simple.JSONObject;

public class LambdaFunctionHandler implements RequestHandler {

@Override
public String handleRequest(Object input, Context context) {
    JSONObject obj = new JSONObject();
    obj.put("statusCode", 200);
    JSONObject headers = new JSONObject();
    headers.put("x-custom-header", "my custom header value");
    obj.put("headers", headers);
    obj.put("body", "Hello from Lambda!");

    return obj.toJSONString();
}

}
````

Remote Configuration Settings:
Transport: Socket
Debugger mode: Attach
Host: 127.0.01
Port: 3000

Invoking the function works fine with a default generated event file, but won't hit the breakpoints. Console output below:
```$ sam local invoke GetFunction --event evt.json
2018/03/12 10:15:57 Successfully parsed template.yml
2018/03/12 10:15:57 Connected to Docker 1.35
2018/03/12 10:15:57 Fetching lambci/lambda:java8 image for java8 runtime...
java8: Pulling from lambci/lambda
Digest: sha256:c2ec8db145bbe44154dbddcdd2976ab8afd60d58d7d633dc98f53f657c0ef909
Status: Image is up to date for lambci/lambda:java8
2018/03/12 10:15:59 Invoking com.amazonaws.lambda.hw.LambdaFunctionHandler::handleRequest (java8)
2018/03/12 10:15:59 Decompressing /*/Hello World/target/hw-1.0.0.jar
2018/03/12 10:16:00 Mounting /private/var/folders/pr/zzhpj48x70l0gk6n1t11x74m0000gn/T/aws-sam-local-1520874959484468000 as /var/task:ro inside runtime container
START RequestId: 28e2a514-e190-4bec-9681-fa194d91e654 Version: $LATEST
END RequestId: 28e2a514-e190-4bec-9681-fa194d91e654
REPORT RequestId: 28e2a514-e190-4bec-9681-fa194d91e654 Duration: 44.77 ms Billed Duration: 100 ms Memory Size: 128 MB Max Memory Used: 9 MB

"{\"headers\":{\"x-custom-header\":\"my custom header value\"},\"body\":\"Hello from Lambda!\",\"statusCode\":200}"
```

This is my first time trying to debug something remotely so I'm not sure what I'm doing wrong. Can anyone help? Thanks in advance.

[michaelj-smith]

I'm not sure if it could be this simple, but make sure that you are passing the debug flag when you execute the sam commands:

$ sam local invoke -d 5858 <function logical id> 

Reference: https://github.com/awslabs/aws-sam-local#debugging-applications

[PaulMaddox]

It hangs after mounting and the page never loads.

This is the intended behaviour. The debugger is configured to break on the first line of code encountered, to give you a chance to attach your debugger.

Hit the URL in the browser, then attach your debugger of choice to the --debug-port specified.

[josephmcasey]

For anyone finding this issue at a later date, I'd like to recommend this online video to help demonstrate the intended behavior @PaulMaddox describes.

[miparnisari]

I created a "remote debug" configuration in IntelliJ that points to port 5000.

I then ran sam local start-lambda -d 5000, and then start clicking on the "debug" button in IntelliJ until the docker container is up.