Deploying Douglas with CGI

Summary

You can run Douglas as a CGI script with many web servers. This document covers setting Douglas up as a CGI script.

Dependencies

You need an account on a web server configured to run CGI scripts. It helps to know how to run CGI scripts on that server, too.

Deployment

  1. Copy the douglas.cgi file from the blog directory (the directory which you created with douglas-cmd create ./blog/) into your CGI directory.

  2. Edit the douglas.cgi file.

    The top of the file looks something like this

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    #!/usr/bin/env python
    
    # -u turns off character translation to allow transmission
    # of gzip compressed content on Windows and OS/2
    #!/path/to/python -u
    
    import os, sys
    
    # Uncomment this line to add the directory your config.py file is
    # in to the python path:
    #sys.path.append("/path/to/directory/")
    

    Make sure the first line points to a valid python interpreter. If you’re using virtualenv, then make sure it points to the python interpreter in the virtual environment.

    Uncomment the sys.path.append("/path/to/directory/") line and make sure the path being appended is the directory that your config.py file is in.

  1. Make sure the douglas.cgi file has the correct permissions and ownership for running a CGI script in this directory for the server that you’re using.

  2. Make sure your blog directory has the correct permissions for being read by the process executing your CGI script.

  3. Run your douglas.cgi script by doing:

    $ ./douglas.cgi test
    

    If that doesn’t work, double-check to make sure you’ve completed the above steps, then check the trouble-shooting section below.

If that does work, then try to run the CGI script from your web browser. The url is dependent on where you put the douglas.cgi script and how CGI works on your web server.

Trouble-shooting

We’re going to try to break this down a bit into categories. Bear with us and keep trying things.

Running ./douglas.cgi doesn’t work

If Python is installed on your system, make sure the first line in douglas.cgi points to the correct Python interpreter. By default, douglas.cgi uses env to execute the Python interpreter. In some rare systems, /usr/bin/env doesn’t exist or the system may have odd environment settings. In those cases, you may edit the first line to point to the Python interpreter directly. For example:

#!/usr/bin/python

Then try running ./douglas.cgi again.

If Python is installed on your system and the first line of douglas.cgi is correct, check for permissions issues. douglas.cgi is a script, so it needs execute permission in order to function. If those aren’t set, then fix that and try running ./douglas.cgi again.

Check the error logs for your web server.

I see a HTTP 404 error when I try to bring up my blog

When you try to look at your blog and you get a HTTP 404 error, then you’re using the wrong URL. Here are some questions to ask yourself:

  • Are you using an .htaccess file?
  • Does your server allow you to run CGI scripts?
  • Do other CGI scripts in this directory work?
  • Does the URL you’re trying to use to access Douglas look like other URLs that work on your system?

I see a HTTP 500 error when I try to bring up my blog

At this point, running ./douglas.cgi at the command prompt should work fine. If you haven’t done that and you’re busy trouble-shooting, go back and review the deployment instructions.

If the problem is with Douglas and not your web server, then you should see a pretty traceback that will help you figure out what the specific problem is.

If the traceback and information doesn’t make any sense to you, add an issue to the issue tracker.

If you don’t see a traceback, then you either have a configuration problem with your web server or a configuration problem with Python. The first thing you should do is check your web server’s error logs. For Apache, look for the error.log file in a place like /var/logs/apache/ or /var/logs/httpd/. If you don’t know where your web server’s error logs are, ask your system administrator.

Does the account your web server runs as have execute access to your douglas.cgi script? If your web server does not have the permissions to read and execute your douglas.cgi script, then your blog will not work.

Do you have plugins loaded? If you do, comment out the load_plugins setting in your config.py file so that Douglas isn’t loading any plugins.

For example:

py["load_plugins"] = ['plugina', 'pluginb', ...]

would get changed to:

# commenting this out to see if it's a plugin problem
# py["load_plugins"] = ['plugina', 'pluginb', ...]

Check to see if the problem persists. Sometimes there are issues with plugins that only show up in certain situations.

I have other issues

Try changing the renderer for your blog to the debug renderer. You can do this by setting the renderer property in your config.py file to debug. For example:

py["renderer"] = "debug"

That will show a lot more detail about your configuration, what the web server passes Douglas in environment variables, and other data about your blog that might help you figure out what your problem is.

If that doesn’t help, add an issue to the issue tracker.

UGH! My blog looks UGLY!

Check out Renderers, Themes and Templates.

I hate writing in HTML!

That’s ok. Douglas supports formatters and entry parsers which allow you to use a variety of markups for writing blog entries. See the documentation on Writing Entries for more information.

Check out Categories.

Advanced installation

We encourage you not to try any of this until you’ve gotten a blog up and running.

This section covers additional advanced things you can do to your blog that will make it nicer. However, they’re not necessary and they’re advanced and we consider these things to be very much a “you’re on your own” kind of issue.

If you ever have problems with Douglas and you ask us questions on the douglas-users or douglas-devel mailing lists, make sure you explicitly state what things you’ve done from this chapter. It’ll go a long way in helping us to help you.

Renaming the douglas.cgi script

In the default installation, the Douglas script is named douglas.cgi.

For a typical user on an Apache installation with user folders turned on, Douglas URLs could look like this:

http://example.com/~joe/cgi-bin/douglas.cgi
http://example.com/~joe/cgi-bin/douglas.cgi/an_entry.html
http://example.com/~joe/cgi-bin/douglas.cgi/dev/another_entry.html

That gets pretty long and it’s not very good looking. For example, telling the URL to your mother or best friend over the phone would be challenging. It would be nice if we could shorten and simplify it.

So, we have some options:

  • Change the name of the douglas.cgi script.
  • And if that’s not good enough for you, use the Apache mod_rewrite module to get URLs internally redirected to the douglas.cgi script.

Both methods are described here in more detail.

Change the name of the douglas.cgi script

There’s no reason that douglas.cgi has to be named douglas.cgi. Let’s try changing it blog. Now our example URLs look like this:

http://example.com/~joe/cgi-bin/blog
http://example.com/~joe/cgi-bin/blog/an_entry.html
http://example.com/~joe/cgi-bin/blog/category1/another_entry.html

That’s better looking in the example. In your specific circumstances, that may be all you need.

You might have to change the base_url property in your config.py file to match the new URL.

Note

The base_url value should NOT have a trailing slash.

If you’re running on Apache, you might have to tell Apache that this is a CGI script even if it doesn’t have a .cgi at the end of it. If you can use .htaccess files to override Apache settings, you might be able to do something like this:

# this allows execution of CGI scripts in this directory
Options ExecCGI

# if the user doesn't specify a file, then instead of doing the
# regular directory listing, we look at "blog" (which is our
# douglas.cgi script renamed)
DirectoryIndex blog

# this tells Apache that even though "blog" doesn't end in .cgi,
# it is in fact a CGI script and should be treated as such
<Files blog>
ForceType application/cgi-script
SetHandler cgi-script
</Files>

You may need to stop and restart Apache for your Apache changes to take effect.

Hiding the .cgi with RewriteRule

Apache has a module for URL rewriting which allows you to convert incoming URLs to other URLs that can be handled internally. You can do URL rewriting based on all sorts of things. See the Apache manual for more details.

In our case, we want all incoming URLs pointing to blog to get rewritten to cgi-bin/douglas.cgi so they can be handled by Douglas. Then all our URLs will look like this:

http://example.com/~joe/blog
http://example.com/~joe/blog/an_entry.html
http://example.com/~joe/blog/category1/another_entry.html

To do this, we create an .htaccess file (it has to be named exactly that) in our public_html directory (or wherever it is that /~joe/ points to). In that file we have the following code:

RewriteEngine on
RewriteRule   ^blog?(.*)$   /~joe/cgi-bin/douglas.cgi$1   [last]

The first line turns on the Apache mod_rewrite engine so that it will rewrite URLs.

The second line has four parts. The first part denotes the line as a RewriteRule. The second part states the regular expression that matches the part of the URL that we want to rewrite. The third part denotes what we’re rewriting the URL to. The fourth part states that after this rule is applied, no future rewrite rules should be applied.

If you do URL rewriting, you may have to set the base_url property in your config.py accordingly. In the above example, the base_url would be http://example.com/~joe/blog with no trailing slash.

For more information on URL re-writing, see the mode_rewrite chapter in the Apache documentation for the version that you’re using.