Phusion Passenger and nginx location blocks

I spent much of yesterday getting Danbooru set up for the new Room 208 imageboard, and one issue in particular wasted a lot of my time. I had nginx configured to serve requests to the Danbooru directory through Phusion Passenger, using the passenger_base_uri directive. No matter what combination of settings I tried, however, Passenger invariably refused to start up. This in turn meant that requests bounced into the application’s public/ directory, leaving me with a 403 when I tried to access the board’s index page.

Now, I’d read somewhere that if a server has a location / block, the passenger_enabled directive has to go inside of it, instead of server:

# Doesn't work
server {
    # ...
    root /my/www/dir;
    passenger_base_uri /booru;
    location / {
        passenger_enabled on;
    }
}

Problem was, of course, that this piece of advice didn’t help, because I had no such block for that server. It turns out, though, that if a directory specified in passenger_base_uri has a corresponding location block, passenger_enabled must be specified there:

server {
    # ...
    root /my/www/dir;
    passenger_base_uri /booru;
    location /booru/ {  # note path change
        passenger_enabled on;
    }
}

In short, if you have a location block corresponding to the root URL of a Passenger application, passenger_enabled belongs inside it. Hope this keeps at least one other person from self-harm.¹