Build basic microservice online store backend with Golang use Api Gateway Pattern - Part 1

Introduction

Hey, fellow developers! 👋 Ever thought about building a microservices architecture but felt overwhelmed by where to start? Worry no more! In this article, we'll build a basic microservices setup using the API Gateway pattern for an online store. And guess what? We'll do it all in Go (Golang)! 🦦

What You'll Learn

By the end of this guide, you’ll know how to:

• Implement the API Gateway pattern in a microservices architecture.
• Use gRPC for seamless communication between services.
• Set up multiple microservices in Go with Docker.
• Connect the dots and make everything work smoothly together!

Why Microservices? Why Go? Why API Gateway? 🤔

Before we dive into the code, let’s talk about why:

• Microservices: Scalability, independent deployment, and flexibility.
• Go: Fast, efficient, and ideal for building microservices.
• **API **Gateway: Centralized entry point to handle all client requests and route them to the appropriate microservice.

Who said that? Me 😂. Just kidding, but you'll soon be quoting this too when your app handles a gazillion users without breaking a sweat! Imagine your API dancing through the traffic while sipping coffee ☕. Yes, that’s the power of Microservices with Go and an API Gateway.

Oke, without further ado let's start it.

1. Setting Up Your Environment 🛠️

• Install and download Go https://go.dev/doc/install
• Use docker for your microservices https://docs.docker.com/engine/install/
• Just use IDE that you want

2. Setup you project

/online-store
├── api-gateway/
├──── cmd/
├────── main.go
├──── internal/
├────── handler/
├──────── handler.go
├── services/
├──── user-service/
├────── cmd/
├──────── main.go
├────── internal/
├──────── handler/
├────────── handler.go
├────── proto/
├──────── user-proto
├────── Dockerfile
├──── <you can add more services>/
├── docker-compose.yml
└── README.md

That's will be the dir structure the project, you can tweak it as you want, later we will also create pb directory do store generated pb file from our proto file.

Clone googleapis https://github.com/googleapis/googleapis, we will need that for our proto later. Just clone in root dir under online-store dir.

git clone https://github.com/googleapis/googleapis.git

3. Building the User Service 👤

• Initiate Go Mod
  Let's use our terminal and initiate our user-service go mod init
  go mod init user-service
  you can change "user-service" with your github url, but we will use it for now.

• Create our first proto file for user
  create a new file under user-service/proto dir with name user.proto, let's use this proto code:
  

syntax = "proto3";

package order;

option go_package = ".";

import "google/api/annotations.proto";

service OrderService {
    rpc GetMyOrder(GetMyOrderRequest) returns (GetMyOrderResponse) {
        option (google.api.http) = {
            get: "/v1/order/my"
        };
    }
}

message GetMyOrderRequest {
    string user_id = 1;
}

message GetMyOrderResponse {
    string  user_id = 1;
    string order_id = 2;
    string product_id = 3;
    int32 quantity = 4;
    float price = 5;
    string status = 6;
}

• Use protoc to generate gRPC First, we need to create pb dir under service/user-service to store our generated grpc files and run this command to generate our gRPC:

protoc --proto_path="services/user-service/proto" \
        --go_out="services/user-service/pb" \
        --go-grpc_out="services/user-service/pb" \
        --grpc-gateway_out="services/user-service/pb" \
        "services/user-service/proto/user.proto"

With that command we will generate 3 files (user_grpc.pb.go, user_pb.go, and user.pb.gw.go) and will place them into services/user-service/pb directory.

But, because we want use the same grpc to our Api Gateway, we need to copy them too into api-gateway/pb directory. You can copy it manually each time you generate grpc, but let's just use script for it.

I create a new dir online-store/scripts to store all scripts. Let's create a new file generate-proto.sh, and put this code:

#!/bin/bash

# Error handling function
handle_error() {
  echo "Error occurred in script at line: $1"
  exit 1
}

# Trap any error and call the handle_error function
trap 'handle_error $LINENO' ERR

# Declare an associative array to map proto directories to their corresponding pb directories
declare -A dir_map=(
  ["services/user-service/proto"]="services/user-service/pb"
  # you can add another directory here
  # e.g ["services/order-service/proto"]="services/order-service/pb"
)

# Define Static Dir Path
GOOGLEAPIS_DIR="googleapis"
API_GATEWAY_PB_DIR="api-gateway/pb"

# Ensure the API_GATEWAY_PB_DIR exists
if [ ! -d "$API_GATEWAY_PB_DIR" ]; then
  mkdir -p "$API_GATEWAY_PB_DIR"
  echo "Directory $API_GATEWAY_PB_DIR created."
else 
  echo "Directory $API_GATEWAY_PB_DIR already exists."
fi

# Loop through the associative array and generate Go code for each proto directory
for proto_dir in "${!dir_map[@]}"; do
  pb_dir="${dir_map[$proto_dir]}"

  # Check if the pb directory exists, if not, create it
  if [ ! -d "$pb_dir" ]; then
    mkdir -p "$pb_dir"
    echo "Directory $pb_dir created."
  else
    echo "Directory $pb_dir already exists."
  fi

  # Process each .proto file in the proto directory
  for proto_file in "$proto_dir"/*.proto; do
    # Ensure the proto file exists
    if [ -f "$proto_file" ]; then
      # Generate Go code for the current proto file
      protoc --proto_path="$proto_dir" \
        --proto_path="$GOOGLEAPIS_DIR" \
        --go_out="$pb_dir" \
        --go-grpc_out="$pb_dir" \
        --grpc-gateway_out="$pb_dir" \
        "$proto_file"
      echo "Generated Go code for $proto_file"

      # Copy the generated Go code to the API Gateway directory
      cp -auv "$pb_dir"/* "$API_GATEWAY_PB_DIR/"
      echo "Copied generated Go code to $API_GATEWAY_PB_DIR from $pb_dir"
    else
      echo "No .proto files found in $proto_dir."
    fi
  done
done

That script will create you a new pb directory if it's does not exist.

Now, lets execute our script:

./scripts/generate-proto.sh

You will need to install some packages:

go get github.com/grpc-ecosystem/grpc-gateway/v2
go get google.golang.org/genproto/googleapis/api
go get .golang.org/protobuf

If you get some error regarding import, do this comman go mod tidy

• Create our user handler code create a user-handler.go file under services/user-services/internal/handler directory, use let's use this simple code:

package handler

import (
    "context"
    "log"

    pb "user-service/pb"

    "google.golang.org/grpc"
)

// server implements the UserServiceServer interface
type server struct {
    pb.UnimplementedUserServiceServer
}

// NewServer creates a new instance of server
func NewServer() pb.UserServiceServer {
    return &server{}
}

// Implement the methods defined in your proto file here
func (s *server) GetUser(ctx context.Context, req *pb.GetUserRequest) (*pb.GetUserResponse, error) {
    // Log the request details
    log.Printf("Received GetUser request with ID: %s", req.GetId())

    // Implement your logic to get user information
    response := &pb.GetUserResponse{
        Id:    req.GetId(),
        Name:  "John Doe",
        Email: "[e-mail]",
    }

    // Log the response details
    log.Printf("Returning GetUser response: %+v", response)

    return response, nil
}

// Implement GetUserProfile method
func (s *server) GetUserProfile(ctx context.Context, req *pb.GetUserProfileRequest) (*pb.GetUserProfileResponse, error) {
    // Log the request details
    log.Printf("Received GetUserProfile request with ID: %s", req.GetId())

    response := &pb.GetUserProfileResponse{
        Id:      req.GetId(),
        Name:    "John Doe",
        Email:   "[e-mail]",
        Phone:   "1234567890",
        Address: "123 Main St",
    }

    // Log the response details
    log.Printf("Returning GetUserProfile response: %+v", response)

    return response, nil
}

// RegisterServices registers the gRPC services with the server
func RegisterServices(s *grpc.Server) {
    pb.RegisterUserServiceServer(s, NewServer())
}

You will need to install some package:

go get google.golang.org/grpc

• Create our main.go file in user-service/cmd/main.go We use this simple code for our main code:

package main

import (
    "log"
    "net"

    "google.golang.org/grpc"
    "google.golang.org/grpc/reflection"

    "user-service/internal/handler"
)

func main() {
    // Create a new gRPC server
    s := grpc.NewServer()

    // Register the server with the gRPC server
    handler.RegisterServices(s)

    // Register reflection service on gRPC server
    reflection.Register(s)

    // Listen on port 50051
    lis, err := net.Listen("tcp", ":50051")
    if err != nil {
        log.Fatalf("failed to listen: %v", err)
    }

    // Start the gRPC server
    log.Println("Starting gRPC server on :50051")
    if err := s.Serve(lis); err != nil {
        log.Fatalf("failed to serve: %v", err)
    }
}

You need to install google.golang.org/grpc/reflection, with this package we can look into our services.

• Create Dockerfile for user-service create a new file in user-service directory with name Dockerfile, use this for our Dockerfile:

# Stage 1: Build
FROM golang:1.23 AS builder

WORKDIR /app

# Copy go mod and sum files
COPY go.mod go.sum ./
RUN go mod download

# Copy the application code
COPY . .

# Build the Go application
RUN go build -o user-service ./cmd

# Stage 2: Run
FROM ubuntu:22.04

# Install necessary libraries
RUN apt-get update && apt-get install -y \
    ca-certificates \
    libc6 \
    && rm -rf /var/lib/apt/lists/*

WORKDIR /app

# Copy the binary from the build stage
COPY --from=builder /app/user-service /app/user-service

ENTRYPOINT ["/app/user-service"]

# Expose port
EXPOSE 50051

4. Build Api Gateway

Because we already have pb files generated under api-gateway/pb directory. Now, we can create handler for our api-gateway, create a new file api-gateway/internal/handler/service-regitry.go, use this code to register our services:

package handler

import (
    "context"
    "log"

    "github.com/grpc-ecosystem/grpc-gateway/v2/runtime"
    "google.golang.org/grpc"

    pb "api-gateway/pb"
)

// ServiceConfig holds the configuration for each service.
type ServiceConfig struct {
    Name    string
    Address string
}

// RegisterServices registers all services with the mux based on the given service configurations.
func RegisterServices(ctx context.Context, mux *runtime.ServeMux, services []ServiceConfig) error {
    for _, svc := range services {
        opts := []grpc.DialOption{grpc.WithInsecure()}
        var err error
        switch svc.Name {
        case "UserService":
            err = pb.RegisterUserServiceHandlerFromEndpoint(ctx, mux, svc.Address, opts)
        // We can create another cases for another services
        default:
            log.Printf("No handler implemented for service %s", svc.Name)
            continue
        }
        if err != nil {
            return err
        }
        log.Printf("Registered service %s at %s", svc.Name, svc.Address)
    }
    return nil
}

You will also need to install these in api-gateway:

go get github.com/grpc-ecosystem/grpc-gateway
go get google.golang.org/grpc

• Create our main.go in Api Gateway Now, create a new file api-gateway/cmd/main.go for our main code, use this code:

package main

import (
    "context"
    "log"
    "net/http"

    "github.com/grpc-ecosystem/grpc-gateway/v2/runtime"

    "api-gateway/internal/handler"
)

func main() {
    // Define service configurations
    services := []handler.ServiceConfig{
        {Name: "UserService", Address: "user-service:50051"},
        // You can add another services here
    }

    ctx := context.Background()
    ctx, cancel := context.WithCancel(ctx)
    defer cancel()

    mux := runtime.NewServeMux()

    // Register services
    if err := handler.RegisterServices(ctx, mux, services); err != nil {
        log.Fatalf("Failed to register services: %v", err)
    }

    // Start the HTTP server
    if err := http.ListenAndServe(":8080", mux); err != nil {
        log.Fatalf("Failed to start HTTP server: %v", err)
    }
}

• Create Dockerfile for Api Gateway We also need Dockerfile for Api Gateway, create a new file api-gateway/Dockerfile and use this config:

# Stage 1: Build
FROM golang:1.23 AS builder

WORKDIR /app

# Copy go mod and sum files
COPY go.mod go.sum ./
RUN go mod download

# Copy the application code
COPY . .

# Build the Go application
RUN go build -o main ./cmd

# Stage 2: Run
FROM ubuntu:22.04

# Install necessary libraries
RUN apt-get update && apt-get install -y \
    ca-certificates \
    libc6 \
    && rm -rf /var/lib/apt/lists/*

WORKDIR /app

# Copy the binary from the build stage
COPY --from=builder /app/main /app/main

ENTRYPOINT ["/app/main"]

# Expose port (if necessary)
EXPOSE 8080

• Create docker-compose.yml Oke, we also need to create a online-store/docker-compose.yml file, use use copy:

version: '4.0'
services:
  api-gateway:
    build: ./api-gateway
    ports:
      - "8080:8080"
    depends_on:
      - user-service

  user-service:
    build: 
      context: ./services/user-service
      dockerfile: Dockerfile
    ports:
      - "50051:50051"

  # Can put another service here

5. Start our Microservice

Because we use docker, make sure your docker already active.
And we can run with this command:

docker-compose up --build -d

You will see your services already up. (I use windows)

You can also use this command to see active service:

docker ps

You see that i also have another services, you can also add it to your code.

6. Hit our endpoint

I use postman to hit user-service endpoint

Because we also put log code in our user-service, we can do this command to look into our service logs:

docker logs --follow user-service-1

Make sure service name by looks into our active service docker ps

Then you will see this log:

Conclusion 🏁

Congratulations! 🎉 You've just built a basic microservices architecture for an online store using Go, gRPC, Docker. Keep experimenting and improving your setup. We will continue to build our online-store until finish, stay tune 🧑‍💻🚀

Repository: https://github.com/agustrinaldokurniawan/online-store/tree/main/backend