/go-app
|-- cmd
|-- internal <-- the app source code
|-- nginx
   |-- nginx.conf
|-- config.json <-- my config file for Viper
|-- docker-compose.yaml
|-- Dockerfile
|-- go.mod
|-- go.sum
|-- main.go

user nginx;
# can handle 1000 concurrent connections
events {
    worker_connections   1000;
}
# forwards http requests
http {
        # http server
        server {
              # listens the requests coming on port 8080
              listen 80;
              access_log  off;
              proxy_request_buffering off;
              proxy_buffering off;
              # / means all the requests have to be forwarded to api service
              location / {
                # resolves the IP of api using Docker internal DNS
                proxy_pass http://rest-api:3000;
                proxy_set_header Host $host;
                proxy_set_header X-Real-IP $remote_addr;
                proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
                proxy_set_header X-Forwarded-Proto $scheme;
              }
        }
}

FROM golang:1.22-alpine AS builder

# working directory (/build).
WORKDIR /build

# dependency using go mod.
COPY go.mod go.sum ./
RUN go mod download

# Copy the code
COPY . .

# environment variables for docker image
# and build the server.
ENV CGO_ENABLED=0 GOOS=linux GOARCH=amd64
RUN apk add --no-cache dumb-init
RUN go build -ldflags="-s -w" -o apiserver ./main.go

FROM alpine:latest

# working directory (/build).
WORKDIR /

# Copy the Pre-built binary file from the previous stage.
COPY --from=builder ["/usr/bin/dumb-init", "/usr/bin/dumb-init"]
COPY --from=builder ["/build/apiserver", "/"]
COPY --from=builder ["/build/config.json", "/config.json"]

# Export necessary port.
EXPOSE 3000

ENTRYPOINT ["/usr/bin/dumb-init", "--"]
CMD ["/apiserver"]

services:
  # service name
  rest-api:
    # Dockerfile location
    build: "."
    # Exposes the port 3000 for internal
    ports:
      - "3000"
    # always restart when the service went down
    restart: always
    # number of replicas
    deploy:
      replicas: 2
  # nginx load balancer
  nginx:
    # latest stable alpine nginx image
    image: nginx:stable-alpine
    # nginx configuration
    volumes:
      - ./nginx/nginx.conf:/etc/nginx/nginx.conf:ro
    # start nginx after the service up successfully
    depends_on:
      - rest-api
    # map the nginx port 80 to docker port 3000
    ports:
      - "3000:80"