Plack::Builder 

# in .psgi
use Plack::Builder;

my $app = sub { ... };

builder {
    enable "Plack::Middleware::AccessLog", format => "combined";
    enable "Plack::Middleware::ContentLength";
    enable "Plack::Middleware::ErrorDocument",
              404 => '/path/to/error_404.html',
              500 => '/path/to/error_500.html';
    enable "Plack::Middleware::Lint";
    enable sub {
        my $app = shift;
        sub {
            my $env = shift;
            $app->($env);
        };
    };
    $app;
};