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How to get automatic SSL for multi tenant applications and websites

In this tutorial you will learn how to setup OpenResty/nginx with on the fly Let’s Encrypt SSL certificate registration and renewal on a Amazon EC2 instance. Point your domain to the IP address of the server and you never need to worry again about SSL. No cronjobs, just pure power of Nginx and Lua.

Starting a Amazon EC2 instance

First we choose a EC2 instance with Amazon Linux and create it with the default settings.

Amazon Ec2 instance

Copy the IPv4 Public IP from the EC2 instance dashboard and connect to your instance using your private key.

ssh -i your_key.pem ec2-user@YOUR_EC2_IP

Install OpenResty

We will need to install OpenResty on the remote instance. What is OpenResty®? OpenResty® is a full-fledged web platform that integrates the standard Nginx core, LuaJIT and many carefully written Lua libraries. Lua gives OpenResty/nginx the power to make automatic SSL possible.

sudo yum-config-manager --add-repo https://openresty.org/package/amazon/openresty.repo
sudo yum install openresty
sudo yum install openresty-resty

On newer Amazon machines I got following error installing OpenResty:

https://openresty.org/package/amazon/2/x86_64/repodata/repomd.xml: \[Errno 14\] HTTPS Error 404 - Not Found

To fix that error you need to edit the repo file with sudo vim /etc/yum.repos.d/openresty.repo and exchange the $releasever placeholder of the baseurl to “latest” baseurl=https://openresty.org/package/amazon/latest/$basearch.

Install LuaRocks

LuaRocks is the package manager we need to install the lua-resty-auto-ssl package.

wget http://luarocks.org/releases/luarocks-2.0.13.tar.gz
tar -xzvf luarocks-2.0.13.tar.gz
cd luarocks-2.0.13/
./configure --prefix=/usr/local/openresty/luajit \
    --with-lua=/usr/local/openresty/luajit/ \
    --lua-suffix=jit \
    --with-lua-include=/usr/local/openresty/luajit/include/luajit-2.1
make
sudo make install

Install ggc

https://github.com/GUI/lua-resty-auto-ssl requires ggc for the installation process so we install it with yum.

sudo yum install gcc

Setup a user group

As lua-resty-auto-ssl needs to write to the directory /etc/resty-auto-ssl we’ll add the user group www to our ec2-user.

sudo groupadd www
sudo usermod -a -G www ec2-user

Install lua-resty-auto-ssl

Using the package manger luarocks we install lua-resty-auto-ssl and create the directory where the library will write it’s files to.

sudo /usr/local/openresty/luajit/bin/luarocks install lua-resty-auto-ssl
sudo mkdir /etc/resty-auto-ssl
sudo chown -R root:www /etc/resty-auto-ssl/
sudo chmod -R 775 /etc/resty-auto-ssl

Generate a self signed fallback certificate

We will need a self signed fallback certificate as a fallback to be able to start nginx.

sudo openssl req -new -newkey rsa:2048 -days 3650 -nodes -x509 \
  -subj '/CN=sni-support-required-for-valid-ssl' \
  -keyout /etc/ssl/resty-auto-ssl-fallback.key \
  -out /etc/ssl/resty-auto-ssl-fallback.crt

Edit nginx.conf

After backing up our original nginx.conf we open vim to insert the required configuration for the server.

sudo mv /usr/local/openresty/nginx/conf/nginx.conf /usr/local/openresty/nginx/conf/nginx.backup.conf
sudo vim /usr/local/openresty/nginx/conf/nginx.conf

Insert following content to the nginx.conf

/usr/local/openresty/nginx/conf/nginx.conf
user ec2-user www;
events {
  worker_connections 1024;
}

http {
  lua_shared_dict auto_ssl 1m;
  lua_shared_dict auto_ssl_settings 64k;
  resolver 8.8.8.8 ipv6=off;

  init_by_lua_block {
    auto_ssl = (require "resty.auto-ssl").new()
    auto_ssl:set("allow_domain", function(domain)
      return true
    end)
    auto_ssl:init()
  }

  init_worker_by_lua_block {
    auto_ssl:init_worker()
  }

  server {
    listen 443 ssl;
    ssl_certificate_by_lua_block {
      auto_ssl:ssl_certificate()
    }
    ssl_certificate /etc/ssl/resty-auto-ssl-fallback.crt;
    ssl_certificate_key /etc/ssl/resty-auto-ssl-fallback.key;
  }

  server {
    listen 80;
    location /.well-known/acme-challenge/ {
      content_by_lua_block {
        auto_ssl:challenge_server()
      }
    }
  }

  server {
    listen 127.0.0.1:8999;
    client_body_buffer_size 128k;
    client_max_body_size 128k;

    location / {
      content_by_lua_block {
        auto_ssl:hook_server()
      }
    }
  }
}

Start OpenResty

As the final step we start OpenResty as a system service.

sudo service openresty start

Change DNS record

To test it out point your domain or subdomain to the IP address of your EC2 instance and open the browser with **https://**subdomain.yourdomain.com.

Automatic SSL OpenResty

Debugging

If you get an error or a invalid certificate checkout what’s happening tailing the nginx error.log. I had some directory rights issues and found it out by watching the error.log while reloading the website with https.

tail -F /usr/local/openresty/nginx/logs/error.log

Conclusion

Thanks to Let’s Encrypt and OpenResty I have now a server that can provide automatic SSL for all of my domains. The only thing I need to do is to point my domain to the IP address of the server. The Nginx server can act as a proxy to forward the requests to other servers which makes this setup perfect for multi tenant applications where multiple domains point to the same server.


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About the author

Alexander Feiglstorfer

Alexander Feiglstorfer

Passionate developer and always in search of the most effective way to resolve a problem. After working 13 years for agencies and SaaS companies using almost every CMS out there he founded Storyblok to solve the problem of being forced to a technology, proprietary template languages and the plugin hell of monolithic systems.