Charles Engelke's Blog

Yesterday I showed how to get a basic static web site hosted on Google AppEngine.  But I need a little bit more than a purely static site.  My blog used to be hosted at engelke.com/blog and http://www.engelke.com/blog, but now it’s at blog.engelke.com.  So any existing links to my blog entries will break.  That is, they’ll break unless requests to engelke.com/blog/something get redirected to blog.engelke.com/something.

I did this with a rewrite rule when my site was being served with the Apache httpd server.  The specific rule I had was:

RewriteRule ^/blog(.*)$  http://blog.engelke.com$1  [R]

That says that a request that starts with /blog will be redirected to one at blog.engelke.com followed by whatever followed the word blog.  Which is actually kind of wrong; for example, this will redirect a request made to engelke.com/blogging to blog.engelke.comging, which is nonsense.  I really should have given two rules:

RewriteRule ^/blog/(.*)$  https://blog.engelke.com/$1 [R]
RewriteRule ^/blog$  https://blog.engelke.com/        [R]

The first rule says that anything starting with /blog/ will be redirected to blog.engelke.com/ followed by whatever was after blog/.  That handles everything but a request to engelke.com/blog just by itself.  The second rule handles that.

AppEngine’s url: mapping rules in app.yaml kind of look like rewrite rules.  For example, the mapping:

- url: (.*)/
  static_files: static\1/index.html

That says any request that ends with a slash should be served with the file at that relative directory followed by index.html.  But that’s not a redirect.  The browser still requests the URL ending with the slash; the server just returns the contents of a particular file.

No, if we want redirection similar to the rewrite rules I had, we’ll need to write an AppEngine script.  First we add two url: mappings to app.yaml.  These should be placed before the existing ones:

- url: /blog/.*
  script: redirector.py

- url: /blog
  script: redirector.py

These correspond to the first part of the old rewrite rules, but they don’t tell what the response should be.  Instead, they just tell AppEngine to run the redirector.py script and let it figure out what to do.

I started writing the redirector.py script with a standard skeleton from the AppEngine documentation:

from google.appengine.ext import webapp
from google.appengine.ext.webapp.util import run_wsgi_app

application = webapp.WSGIApplication(
            [
            # pattern to handler mapping pairs go here
            ])

def main():
   run_wsgi_app(application)

if __name__ == "__main__":
    main()

The “pattern to hander mapping pairs” are each a string that’s a regular expression to match and the name of a class to handle those request paths.  The following two lines match both patterns and invoke the BlogHandler class for them (the ‘r’ in front a string just tells Python it’s a “raw” string, so Python doesn’t interpret any characters in any special way):

     (r'^/blog/(.*)', BlogHandler),
     (r'^/blog$',     BlogHandler)

The BlogHandler class contains methods for each HTTP method to be handled.  We’ll just handle GET and HEAD requests, since those are the only kind our blog will respond to anyway.  The pattern matched inside the parentheses will be passed as a parameter to each of these methods (and self is always going to be passed as the first parameter in Python).  The second pattern doesn’t have any parentheses, so that matching string parameter will be missing; our handlers will have to accept that.

Here’s the code for the BlogHandler class:

class BlogHandler(webapp.RequestHandler):
    def get(self, tail = ''):
        self.redirect('https://blog.engelke.com/'+tail, permanent = True)
    def head(self, tail = ''):
        self.redirect('https://blog.engelke.com/'+tail, permanent = True)

This code is pretty simple and should be self-explanatory.  If no second parameter is given, the methods act as if an empty string was passed.  The optional “permanent = True” parameter makes the redirect an HTTP status 301 Moved Permanently so that client programs can know to never bother to look at the old address.

Complete code

The new app.yaml file is:

application: engelkeweb
version: 1
runtime: python
api_version: 1

handlers:
- url: /blog/.*
  script: redirector.py

- url: /blog
  script: redirector.py

- url: (.*)/
  static_files: static\1/index.html
  upload: static/index.html

- url: /
  static_dir: static

The redirector.py script is:

from google.appengine.ext import webapp
from google.appengine.ext.webapp.util import run_wsgi_app

class BlogHandler(webapp.RequestHandler):
    def get(self, tail = ''):
        self.redirect('https://blog.engelke.com/'+tail, permanent = True)
    def head(self, tail = ''):
        self.redirect('https://blog.engelke.com/'+tail, permanent = True)

application = webapp.WSGIApplication(
            [
                (r'^/blog/(.*)', BlogHandler),
                (r'^/blog$',     BlogHandler)
            ])

def main():
   run_wsgi_app(application)

if __name__ == "__main__":
    main()

And that’s my AppEngine hosted web site.  The one problem left is that requests that should have a trailing slash, but don’t, won’t work (other than /blog, handled above).  But there are only two such possible pages on my site, and I’ve never posted links without the trailing slashes.  So I don’t need to deal with them.

Though I did.  I just added mappings for those two raw names (/xhtmlref and /charles/TPC5) to the redirector.py script, and added a class to redirect those requests to the right URL with the trailing slash.  But that doesn’t show any new ideas, so I’m not going to put the additional code here.

Shortly after I first got my own domain I decided to run all the services myself.  It was a good experience but eventually got old, so I’ve been migrating everything to hosted services.  Free hosted services if possible.

DNS went first.  When I first registered my domain the registrar would only register my nameservers, which I then had to manage.  But now they (and apparently all registrars) will manage my nameservers for me through a simple web dashboard.  Step one was done and it was free as part of my domain registration.

Next came e-mail.  Before I ran my own mail servers I had a mail hosting provider, which cost $25 per month back then.  But now I can get mail hosting for free from Google Apps.  It’s easy to use and works great.  If you don’t have your own domain name, you can also register one through them for just $10 per year.

I’d been running my own Movable Type installation for my blog.  I considered moving to hosted TypePad, but I’d heard good things about WordPress.  WordPress.com now hosts my blog, also for free, but I decided to pay $10 per year to have it at my own domain name.  I love their service.

And now I’d migrated everything but my core web site, which is very minimal.  All I’ve got is a home page and a small number of other pages, because I’d already migrated my photos to Picasa web albums and my presentation files to Google Docs (which is also available as part of Google Apps), all for free.  There is one hitch, though: when I moved to a hosted blog all my old URLs changed, so my main web site has to redirect requests for the old URLs to the correct new ones.  But still, I didn’t want to pay for full web hosting for what is essentially just a starting point.

Google AppEngine to the rescue.  It’s a neat platform for a fancy web application, but it can also be a minimal web server.  It’s hosting my site now, and here’s what’s involved in doing it.

First, register an application name for AppEngine.  You’ll need a regular Google Mail account for this, but that’s easy to get.  It doesn’t matter what you call it; mine was engelkeweb.

Next, create a local folder on your machine to hold your application.  Put a folder inside that containing all your web pages.  It can be called anything, but the AppEngine examples always call it static, so that’s what I’ll do.  If your application folder is at C:\MyAppEngine then this folder will be C:\MyAppEngine\static, and the main home page would probably be C:\MyAppEngine\static\index.html.

Now create a text file called app.yaml in the main folder (in this example, at C:\MyAppEngine\app.yaml) with the following contents (change the engelkeweb entry to the name you registered):

application: engelkeweb
version: 1
runtime: python
api_version: 1

handlers:
- url: (.*)/
  static_files: static\1/index.html
  upload: static/index.html

- url: /
  static_dir: static

Now upload your application (actually, just the static pages and the app.yaml file) using the command:

appcfg.py update C:\MyAppEngine

Voila!  You’ve got a simple static web site.  The second handler specification (for url: /, handled by static_dir: static) means that AppEngine will serve the page static\folder\xyz.ext whenever a user requests http://engelkeweb.appspot.com/folder/xyz.ext.  That’s 95% of a static web site. And the first handler specification (for url: (.*)/) says that any request to a URL ending with a slash should return the index.html page in that folder.  So a request to http://engelkeweb.appspot.com/folder/ would return the file static\folder\index.html.

Note that the order of the handler specifications matter, since the first one matched is what is returned.

You can use your Google Apps settings page to make this site available at your domain’s normal address, too (so in my case, that same page is returned for http://www.engelke.com/folder/xyz.ext and http://engelke.com/folder/xyz.ext).  You have to set up some DNS entries for that, but the Google Apps pages give clear explanations of what to do.

That’s how I’m now serving up engelke.com.  But what about the redirection for my blog pages?  Every URL of the form http://engelke.com/blog/something should now be redirected to https://blog.engelke.com/something.  Doing that requires actually writing a very simple Python handler for the site, just 20 lines long, and adding another handler specification in the app.yaml file.  I’ll cover that in my next post.