Use Google App Engine and Golang to Host a Static Website with Same Domain Redirects

There are several inexpensive ways to host a static website generated with a static site generator like Jekyll, Hugo, or Pelican:

This entire blog is statically generated using Jekyll. However, I am unable to use any of the options above, because, over this blog’s lifetime, I have changed domain names, changed URL schemes, and renamed posts, and I want to keep alive all of the old URLs.

I have been hosting this blog using Apache and, more recently, nginx on a single virtual machine, and the redirection features of either piece of software work just fine, but I was ready to host it somewhere new and different.

A previous post details how I redirect URLs from an old domain to a new domain using Google App Engine and Python, but now I needed a way to serve static content and redirect URLs from the same domain. That same domain redirection requirement is why I cannot simply use Google App Engine’s static content only feature (linked in the list above). However, I can use Google App Engine in combination with a simple Golang application to serve both static content and same domain redirects.

Why Google App Engine?

Before you dive into the rest of the post, perhaps you are wondering, why host a blog on Google App Engine? Here are my reasons why:

  • If your traffic fits within App Engine’s free tier of 28 instance hours and 1 GB of egress traffic per day, hosting the blog is practically free
  • Pushing updates is done with one command
  • Logging and monitoring are integrated using Stackdriver
  • Automatic up and down scaling based on traffic patterns
  • With a few clicks, web logs can easily be pushed to something like BigQuery for long term storage and ad hoc analysis
  • Managed SSL certificates using Let’s Encrypt

Prerequisites

This post assumes the following:

  • You are familiar with Google Cloud Platform (GCP) and have already created a GCP Project
  • You have installed the Google Cloud SDK
  • You have authenticated the gcloud command against your Google Account

Create a GCP Project

If you have not yet created a GCP Project, follow these steps:

  1. Open a web browser, and create or log in to a Google Account
  2. Navigate to the GCP Console
  3. If this is your first GCP Project, you will be prompted to create a GCP Project. Each Google Account gets $300 in credit to use within 12 months towards GCP. You are required to enter a credit card to create a GCP Project, but it will not be charged until the $300 credit is consumed or 12 months expire.
  4. If this is a new GCP Project, you will need to enable the Compute Engine API by navigating to the Compute Engine section of the GCP Console and wait for initialization to complete

Install the Google Cloud SDK

If you have not yet installed the Google Cloud SDK, follow the instructions here.

Authenticate gcloud

Once you have created a GCP Project and installed the Google Cloud SDK, the last step is to authenticate the gcloud command to your Google Account. Open your terminal application and run the following command:

gcloud auth login

A web page will open in your web browser. Select your Google Account and give it permission to access GCP. Once completed, you will be authenticated and ready to move forward.

Create a Directory

Next, create a directory somewhere on your workstation to store your Google App Engine application:

mkdir ~/Sites/example.com/app_engine

Change into that directory:

cd ~/Sites/example.com/app_engine

The remainder of this post will assume you are working inside of this directory.

Additionally, create a directory inside of the app_engine directory called static:

mkdir ~/Sites/example.com/app_engine/static

You will revisit this directory later.

Create app.yaml

Google App Engine typically requires two files: app.yaml and an application file written in Python, Golang, Java, or PHP - in this case it’s going to be Golang.

app.yaml provides the necessary configuration to run your application. There are a lot of different parameters that can exist in app.yaml. Those parameters might differ based on the programming language used. For this post, Golang will be used, and you can find all the available Golang parameters here.

Create file app.yaml with the following contents:

runtime: go
api_version: go1

handlers:
- url: /.*
  script: _go_app
  secure: always
  redirect_http_response_code: 301

Notice that secure: always has been set. This means the Golang application will always be served over HTTPS. If an end user navigates to the web application over HTTP, they will by default be 302 redirected to the HTTPS version. This is why redirect_http_response_code: 301 has also been set. I always want the web application to be served over HTTPS, and I do not want search engines interpreting the redirection from HTTP to HTTPS as a temporary redirect; it is a permanent redirect.

If you have static assets, and you probably do, it is best practice to inform App Engine of this and let it serve those assets from object storage instead of from your application. Doing this is easy and is also done through the app.yaml file.

For example, if you have a favicon file, a CSS directory, a Javascript directory, and an images directory, use the following app.yaml file:

runtime: go
api_version: go1

handlers:
- url: /favicon.png$
  static_files: static/favicon.png
  upload: static/favicon.png

- url: /css
  static_dir: static/css

- url: /js
  static_dir: static/js

- url: /images
  static_dir: static/images

- url: /.*
  script: _go_app
  secure: always
  redirect_http_response_code: 301

Create main.go

Next, you need the Golang application file.

For the following code to meet your needs, create file main.go, copy and paste the code below, and make the following modifications:

  • In the domain variable, change the value to match your domain name with the correct HTTP protocol.
  • In the urls map, replace all of the key value pairs to match the redirects you need in place. Replace each key with just the path portion (/example-post-1.html instead of https://example.com/example-post-1.html) of the current domain’s old URL you want to keep alive. Then replace each value with the path portion of current domain’s new URL you want to redirect to.

All redirects will be 301 redirects. This can be modified by changing 301 in the code below to a different HTTP redirect status code such as 302.

package main

import (
    "net/http"
    "os"
    "strings"
)

func init() {
    http.HandleFunc("/", handler)
}

func handler(w http.ResponseWriter, r *http.Request) {
    // True (ok) if request path is in the urls map
    if value, ok := urls[r.URL.Path]; ok {
        value = domain + value
        http.Redirect(w, r, value, 301)
    } else {
        path := "static/" + r.URL.Path
        // Return 403 if HTTP request is to a directory that exists and does not contain an index.html file
        if f, err := os.Stat(path); err == nil && f.IsDir() {
            index := strings.TrimSuffix(path, "/") + "/index.html"
            if _, err := os.Open(index); err != nil {
                w.WriteHeader(403)
                w.Write([]byte("<html><head><title>403 Forbidden</title></head><body><center><h1>403 Forbidden</h1></center></body></html>"))
                return
            }
        }

        // Return custom 404 page if HTTP request is to a non-existant file
        if _, err := os.Stat(path); os.IsNotExist(err) {
            w.WriteHeader(404)
            http.ServeFile(w, r, "static/404.html")
            return // Without naked return, a "404 page not found" string will be displayed at the bottom of your custom 404 page
        }

        http.ServeFile(w, r, path)
        return
    }
}

var domain string = "https://example.com"

var urls = map[string]string{
            "/example-post-1.html": "/post/example-post-1.html",
            "/example-post-2.html": "/post/example-post-2.html",
            "/example-post-3.html": "/post/example-post-3.html",
}

Generate the Static Content

With app.yaml and main.go saved, the last piece is to generate your static content and store it in the static directory you created earlier.

How you do this entirely depends on what static site generator you are using.

If you are using Jekyll, you can configure the destination parameter in Jekyll’s _config.yml file to save your static content in any directory on your workstation. So, you could set the destionation parameter to ~/Sites/example.com/app_engine/static, and, everytime you run jekyll build, the static content will be saved in that directory.

Deploy to App Engine

With app.yaml, main.go, and your static content generated, you are ready to deploy your Google App Engine application.

Assuming gcloud is already pointed at the Google Cloud Project you want to deploy to, verify with gcloud config list project, run the following command:

gcloud app deploy

The command will output the appspot URL your application will be deployed to and ask if you want to continue. Typically, the appspot URL is https://your-project-id.appspot.com. This is also a useful self-check to make sure you are not deploying your application to the wrong Google Cloud Project. If everything looks okay, type Y and Enter to deploy your application. Depending on how large your static content is, your application should be deployed within about one minute.

Setup DNS

At this point, your application is deployed under URL https://your-project-id.appspot.com. Unless your website uses that as its domain name, you will probably want to setup a custom domain that uses your actual current domain name.

The App Engine section of the Google Cloud Console can be used to do this. Go here and follow the instructions to configure your custom domain.

Once that is complete and DNS has had time to propagate, you should be able to navigate in your web browser to one of your current domain’s old URLs, for example https://example.com/example-post-1.html, and have it redirect to your current domain’s new URLs, for example https://example.com/post/example-post-1.html.

Pushing Updates

To push updates, make the necessary changes in your static site’s source directory, regenerate the static content, and redeploy to Google App Engine by changing into the ~/Sites/example.com/app_engine directory and running gcloud app deploy.

References