Самописный сертификат ssl для nginx ubuntu
Генерим

openssl req -x509 -nodes -days 365 -newkey rsa:2048 -keyout nginx.key -out nginx.crt

Редактим конфиг

server {
        listen 80 default_server;
        listen [::]:80 default_server ipv6only=on;
        listen 443 ssl;
        root /usr/share/nginx/html;
        index index.html index.htm;
        server_name your_domain.com;
        ssl_certificate /etc/nginx/ssl/nginx.crt;
        ssl_certificate_key /etc/nginx/ssl/nginx.key;
        location / {
                try_files $uri $uri/ =404;
        }
}