serverless offline golang setup

#serverless #go

Recently i have faced an issue in running the serverless application built using GoLang in offline(locally).

So, i just want to share the detailed steps

Initial Setup

Pre requisites

Serverless package should be installed globally
Golang
Make sure you're in your ${GOPATH}/src directory

take a sample application setup from aws examples

$ serverless create -t aws-go-dep -p <your project name>

Add a Makefile in root directory

.PHONY: build clean deploy
build:
    env GOOS=linux go build -ldflags="-s -w" -o <your bunary path>
clean:
    rm -rf ./bin
deploy: clean build
    sls deploy --verbose

Add package.json file in the project root directory

{
    "name": "lambda-golang-offline",
    "description": "To run the golanf lambda service locally",
    "version": "1.0.0",
    "scripts": {
        "start": "node ./node_modules/.bin/serverless offline start --useDocker",
        "watch": "nodemon --watch ./ -e go,js --exec make build"
    },
    "devDependencies": {
        "nodemon": "^2.0.3",
        "serverless": "^1.70.0",
        "serverless-offline": "^6.1.5"
    }
}

Now install the npm dependencies using the command

$ npm i

Now build the binary

$ make build

Now start the server

$ npm start

for the first time it will take time. wait and then hit the api in postman

while development use watch

$ npm run watch

serverless.yaml looks like this

service: returns
frameworkVersion: '>=1.28.0 <2.0.0'
provider:
  name: aws
plugins:
  - serverless-offline
package:
  exclude:
    - ./**
  include:
    - ./bin/**
functions:
  return:
    runtime: go1.x
    handler: <your handler>
    environment:
      env: ${opt:stage, self:provider.stage}
      IS_OFFLINE: false
    events:
      - http: 
          path: /<desires path>
          method: post
          cors:
            origins:
            - "*"
            headers:
            - Content-Type
            - X-Amz-Date
            - Authorization
            - X-Api-Key
            - X-Amz-Security-Token
            - X-Amz-User-Agent

if you are planning to use api gateway endpoints in front end then you should add the cors policy in serverless.yaml file
instaed of * use the relevant origin names

you can find all the files in git

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