Setting up nginx on the Dokku droplet to show 404 errors

Just return 404 in whatever block you want.

server {
        listen 80 default_server;

        return 404;
}

Thanks to help from @memnochxx, I’ve been able to get a working dokku nginx configuration that can deliver 404 pages for both http and https requests for any unknown pages or vhost’s (this is on Ubuntu 14.04 running Dokku v0.5.5).

Firstly, the /etc/nginx/nginx.conf is the file that needs to be modified in order to return 404. As explained in the dokku nginx documentation, you’ll need to place the 404 return before the virtual hosts config in the primary http block. The result should look like this:

##
# Custom 404 return for requests made to any URL or vhost
# that doesn't exist or match a dokku application.
#
# Make sure that this goes above "Virtual Host Configs"
##

server {
	listen 80 default_server;
	listen [::]:80 default_server ipv6only=on;
	listen 443 default_server ssl;
	ssl_certificate /etc/nginx/ssl/fake.crt;
	ssl_certificate_key /etc/nginx/ssl/fake.pem;
	return 404;
}

##
# Virtual Host Configs
##

include /etc/nginx/conf.d/*.conf;
include /etc/nginx/sites-enabled/*;

We’ll also need to generate some dummy self-signed SSL certificates to get the https 404 working. We’ll throw those in the /etc/nginx/ssl directory. Run the following commands to do that:

cd /etc/nginx
mkdir ssl
cd ssl
openssl req -x509 -newkey rsa:2048 -keyout fake.pem -out fake.crt -days 365

The days for the openssl command don’t really matter, as the certificate will be invalid anyway. Just run through the default options and don’t worry about the content of the certificate. We’re only putting them there to make nginx happy because it requires a certificate and an associated key to listen on 443. Hope this helped, and thank you again @memnochxx for your help earlier!