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How To Host a Website Using Cloudflare and Nginx on Ubuntu 16.04

PostedMarch 15, 2018 7k views Nginx Security Ubuntu 16.04

The author selected the Electronic Frontier Foundation to receive a $200 donation as part of the Write for DOnations program.

Introduction

Cloudflare is a service that sits between the visitor and the website owner's server, acting as a reverse proxy for websites. Cloudflare provides a Content Delivery Network (CDN), as well as DDoS mitigation and distributed domain name server services.

Nginx is a popular web server responsible for hosting some of the largest and highest-traffic sites on the internet. It's common for organizations to serve websites with Nginx and use Cloudflare as a CDN and DNS provider.

In this tutorial you will secure your website served by Nginx with an Origin CA certificate from Cloudflare and configure Nginx to use authenticated pull requests. The advantages of using this setup are that you benefit from Cloudflare's CDN and fast DNS resolution while ensuring that all connections pass through Cloudflare. This prevents any malicious requests from reaching your server.

Prerequisites

To complete this tutorial, you'll need the following:

Step 1 — Generating an Origin CA TLS Certificate

The Cloudflare Origin CA lets you generate a free TLS certificate signed by Cloudflare to install on your Nginx server. By using the Cloudflare generated TLS certificate you can secure the connection between Cloudflare's servers and your Nginx server.

To generate a certificate with Origin CA, navigate to the Crypto section of your Cloudflare dashboard. From there, click on the Create Certificate button in the Origin Certificates section:

Create certificate option in the Cloudflare dashboard

Leave the default option of Let CloudFlare generate a private key and a CSR selected.

Origin CA GUI options

Click Next and you will see a dialog with the Origin Certificate and Private key. You need to transfer both the origin certificate and private key from CloudFlare to your server.

Dialog showing the origin certificate and private key

We'll use the /etc/ssl/certs directory on the server to hold the origin certificate. The /etc/ssl/private directory will hold the private key file. Both folders already exist on the server.

First, copy the contents of the Origin Certificate displayed in the dialog box in your browser.

Then, on your server, open /etc/ssl/certs/cert.pem for editing:

  • sudo nano /etc/ssl/certs/cert.pem

Paste the certificate contents into the file. Then save and exit the editor.

Then return to your browser and copy the contents of the Private key. Open the file /etc/ssl/private/key.pem for editing:

  • sudo nano /etc/ssl/private/key.pem

Paste the key into the file, save the file, and exit the editor.

Warning: Cloudflare's Origin CA Certificate is only trusted by Cloudflare and therefore should only be used by origin servers that are actively connected to Cloudflare. If at any point you pause or disable Cloudflare, your Origin CA certificate will throw an untrusted certificate error.

Now that you copied the key and certificate files to your server, you need to update the Nginx configuration to use them.

Step 2 — Installing the Origin CA certificate in Nginx

In the previous section, you generated an origin certificate and private key using Cloudlfare's dashboard and saved the files to your server. Now you'll update the Nginx configuration for your site to use the origin certificate and private key to secure the connection between Cloudflare's servers and your server.

Nginx creates a default server block during installation. Remove it if it exists, as you've already configured a custom server block for your domain:

  • sudo rm /etc/nginx/sites-enabled/default

Next, open the Nginx configuration file for your domain:

  • sudo nano /etc/nginx/sites-available/example.com

The file should look like this:

example.com'>/etc/nginx/sites-available/example.com
server {
        listen 80;
        listen [::]:80;

        root /var/www/example.com/html;
        index index.html index.htm index.nginx-debian.html;

        server_name example.com www.example.com;

        location / {
                try_files $uri $uri/ =404;
        }
}

We'll modify the Nginx configuration file to do the following:

  • Listen on port 80 and redirect all requests to use https.
  • Listen on port 443 and use the origin certificate and private key that you added in the previous section.

Modify the file so it looks like the following:

example.com'>/etc/nginx/sites-available/example.com
server {
    listen 80;
    listen [::]:80;
    server_name example.com www.example.com;
    return 302 https://$server_name$request_uri;
}

server {

    # SSL configuration

    listen 443 ssl http2;
    listen [::]:443 ssl http2;
    ssl        on;
    ssl_certificate         /etc/ssl/certs/cert.pem;
    ssl_certificate_key     /etc/ssl/private/key.pem;

    server_name example.com www.example.com;

    root /var/www/example.com/html;
    index index.html index.htm index.nginx-debian.html;


    location / {
            try_files $uri $uri/ =404;
    }
}

Save the file and exit the editor.

Next, test to make sure that there are no syntax errors in any of your Nginx configuration files:

  • sudo nginx -t

If no problems were found, restart Nginx to enable your changes:

  • sudo systemctl restart nginx

Now go to the Cloudflare dashboard's Crypto section and change SSL mode to Full. This informs Cloudflare to always encrypt the connection between Cloudflare and your origin Nginx server.

Enable Full SSL mode in the Cloudflare Dashboard

Now visit your website at https://example.com to verify that it's set up properly. You'll see your home page displayed, and the browser will report that the site is secure.

In the next section, you will set up Authenticated Origin Pulls to verify that your origin server is indeed talking to Cloudflare and not some other server. By doing so, Nginx will be configured to only accept requests which use a valid client certificate from Cloudflare and requests which have not passed through CloudFlare will be dropped.

Step 3 — Setting Up Authenticated Origin Pulls

The Origin CA certificate will help Cloudflare verify that it is talking to the correct origin server. But how can your origin Nginx server verify that it is actually talking to Cloudflare? Enter TLS Client Authentication.

In a client authenticated TLS handshake, both sides provide a certificate to be verified. The origin server is configured to only accept requests that use a valid client certificate from Cloudflare. Requests which have not passed through Cloudflare will be dropped as they will not have Cloudflare's certificate. This means that attackers cannot circumvent Cloudflare's security measures and directly connect to your Nginx server.

Cloudflare presents certificates signed by a CA with the following certificate:

-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----

You can also download the certificate directly from Cloudflare here.

Copy this certificate.

Then create the file /etc/ssl/certs/cloudflare.crt file to hold Cloudflare's certificate:

  • sudo nano /etc/ssl/certs/cloudflare.crt

Paste the certificate into the file. Then save the file and exit the editor.

Now update your Nginx configuration to use TLS Authenticated Origin Pulls. Open the configuration file for your domain:

  • sudo nano /etc/nginx/sites-available/example.com

Add the ssl_client_certificate and ssl_verify_client directives as shown in the following example:

example.com'>/etc/nginx/sites-available/example.com
. . .

server {

    # SSL configuration

    listen 443 ssl http2;
    listen [::]:443 ssl http2;
    ssl        on;
    ssl_certificate         /etc/ssl/certs/cert.pem;
    ssl_certificate_key     /etc/ssl/private/key.pem;
    ssl_client_certificate /etc/ssl/certs/cloudflare.crt;
    ssl_verify_client on;

    . . .

Save the file and exit the editor.

Next, test to make sure that there are no syntax errors in your Nginx configuration.

  • sudo nginx -t

If no problems were found, restart Nginx to enable your changes:

  • sudo systemctl restart nginx

Finally, to enable Authenticated Pulls, open the Crypto section in the Cloudflare dashboard and toggle the Authenticated Origin Pulls option .

Enable Authenticated Origin Pulls

Now visit your website at https://example.com to verify that it was set up properly. As before, you'll see your home page displayed.

To verify that your server will only accept requests signed by Cloudflare's CA, toggle the Authenticated Origin Pulls option to disable it and then reload your website. You should get the following error message :

Error message

Your origin server raises an error if a request is not signed by Cloudflare's CA.

Now that you know it works properly, return to the Crypto section in the Cloudflare dashboard and toggle the Authenticated Origin Pulls option again to enable it.

Conclusion

In this tutorial you secured your Nginx-powered website by encrypting traffic between Cloudflare and the Nginx server using an Origin CA certificate from Cloudflare. You then set up Authenticated Origin Pulls on the Nginx server to ensure that it only accepts requests from Cloudflare's servers, preventing anyone else from directly connecting to the Nginx server.

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