How to debug and run multiple lambdas locally - aws-lambda

Question

I would like to build .NET HTTP API using aws lambdas. These lambdas will be called by UI and some other systems via api gateway. Obviously in local environment I would like to run/debug these.
What I have tried:
a) Using the mock tool that comes with AWS Visual Studio templates. You can call individual lambdas but I couldn't figure out how I can call them from e.g. postman using normal rest calls. I don't know how mock tool makes those calls as chrome/firefox doesn't show them.
b) Using sam local start-api. Here is what I did:
sam --version
SAM CLI, version 1.22.0
sam init (choose aws quick start template, package type Image and amazon/dotnet5.0-base as base image)
I can build the solution with sam build, run it wit sam local start-api and I can browse to http://localhost:3000/hello and it works. Problem is that I would need to do build in VS + do those steps every time I change code. Also no easy way to attach debugger.
So what is the recommended way to do this? I know you can run whole .NET web api inside lambda but that doesn't sound like a good technical solution. I am assuming I am not the first person building HTTP api using lambdas.

Answer 1

It might be worth considering running a lambda-like environment in Docker.
While including the dotnet tools you need might not be feasable in actual Lambda, It might be feasible to either include them in a Docker image, or bind mounted to a docker container. These images from lambci can help with that: https://hub.docker.com/r/lambci/lambda/

Answer 2

You can use sam local
https://github.com/thoeni/aws-sam-local
Create API with API gateway example
Resources:
ApiGatewayToLambdaRole:
Type: AWS::IAM::Role
Properties:
AssumeRolePolicyDocument:
Statement:
- Action: ['sts:AssumeRole']
Effect: Allow
Principal:
Service: ['apigateway.amazonaws.com']
Version: '2012-10-17'
ManagedPolicyArns:
- arn:aws:iam::aws:policy/service-role/AWSLambdaRole
- arn:aws:iam::aws:policy/service-role/AmazonAPIGatewayPushToCloudWatchLogs
ApiGateway:
Type: AWS::Serverless::Api
Properties:
StageName: test
EndpointConfiguration: REGIONAL
DefinitionBody:
swagger: "2.0"
info:
title: "TestAPI"
description: TestAPI description in Markdown.
paths:
/create:
post:
x-amazon-apigateway-integration:
uri:
!Sub arn:aws:apigateway:${AWS::Region}:lambda:path/2015-03-31/functions/${MyLambda.Arn}/invocations
credentials: !GetAtt ApiGatewayToLambdaRole.Arn
responses: {}
httpMethod: POST
type: aws
x-amazon-apigateway-request-validators:
Validate query string parameters and headers:
validateRequestParameters: true
validateRequestBody: false
LambdaRole:
Type: AWS::IAM::Role
Properties:
AssumeRolePolicyDocument:
Statement:
- Action: ['sts:AssumeRole']
Effect: Allow
Principal:
Service: [lambda.amazonaws.com]
Version: '2012-10-17'
Path: /
Policies:
- PolicyName: CodeBuildAccess
PolicyDocument:
Version: '2012-10-17'
Statement:
- Action:
- logs:*
- lambda:*
- ec2:CreateNetworkInterface
- ec2:DescribeNetworkInterfaces
- ec2:DeleteNetworkInterface
Effect: Allow
Resource: "*"
Version: '2012-10-17'
MyLambda:
Type: AWS::Serverless::Function
Properties:
Role: !GetAtt LambdaRole.Arn
Handler: myfunctionname.lambda_handler
CodeUri: ./src/myfunctionname
Events:
SCAPIGateway:
Type: Api
Properties:
RestApiId: !Ref ApiGateway
Path: /create
Method: POST
...
Build :
Time sam build --use-container --template backend/template.yam
Invoke Lambda Locally:
The command to invoke Lambda locally is sam local invoke and -e flag is used to specify the path to the Lambda event.
$ sam local invoke -e event.json
When it is run, it will look something like this:
$ sam local invoke MyLambda -e event.json
2021-04-20 11:11:09 Invoking index.handler
2021-04-20 11:11:09 Found credentials in shared credentials file:
~/.aws/credentials
https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/serverless-sam-cli-using-invoke.html
https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/serverless-sam-cli-using-start-api.html
https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/serverless-sam-cli-using-debugging.html
https://github.com/ashiina/lambda-local