Docker Multi-Stage Builds: Smaller, Secure Production Images

It looks like you have a comprehensive guide on using Docker multi-stage builds to optimize your Go application. Let's break down each part of this example, ensuring clarity and completeness.

Step-by-Step Guide

1. Application Code (main.go)

Your main.go file sets up a simple HTTP server that responds with the version number passed as an environment variable:

go
 
1package main
2
3import (
4	"fmt"
5	"log"
6	"net/http"
7	"os"
8)
9
10func main() {
11	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
12		appVersion := os.Getenv("APP_VERSION")
13		if appVersion == "" {
14			appVersion = "unknown"
15		}
16		fmt.Fprintf(w, "Hello from Go, version %s!\n", appVersion)
17	})
18
19	port := os.Getenv("PORT")
20	if port == "" {
21		port = "8080"
22	}
23	log.Printf("Server starting on port %s...", port)
24	log.Fatal(http.ListenAndServe(":"+port, nil))
25}

2. Dockerfile

Your Dockerfile is divided into two stages: a build stage and a release/runtime stage.

Build Stage

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