How to set up Let’s Encrypt for a Go server application

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This is the minimal automatic setup of an HTTPS server using Go and Let’s Encrypt certificates I have found:

package main

import (
    "crypto/tls"
    "log"
    "net/http"

    "golang.org/x/crypto/acme/autocert"
)

func main() {
    certManager := autocert.Manager{
        Prompt:     autocert.AcceptTOS,
        HostPolicy: autocert.HostWhitelist("example.com"), //Your domain here
        Cache:      autocert.DirCache("certs"),            //Folder for storing certificates
    }

    http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
        w.Write([]byte("Hello world"))
    })

    server := &http.Server{
        Addr: ":https",
        TLSConfig: &tls.Config{
            GetCertificate: certManager.GetCertificate,
            MinVersion: tls.VersionTLS12, // improves cert reputation score at https://www.ssllabs.com/ssltest/
        },
    }

    go http.ListenAndServe(":http", certManager.HTTPHandler(nil))

    log.Fatal(server.ListenAndServeTLS("", "")) //Key and cert are coming from Let's Encrypt
}

More information on the autocert package: link

EDIT: Needed to make http available because of letsencrypt security issue, read more here. As a bonus of this fix we now have http–>https redirect. The old example will continue to work if you have already received certificates on it, but it will break for new sites.

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