NodeBalancer SSL Configuration

Updated , by Joel Kruger

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NodeBalancer SSL Configuration.

This guide will help you install an SSL certificate on your NodeBalancer. It includes step-by-step instructions for configuring a NodeBalancer to redirect all web connections over port 443/HTTPS using SSL. The provided directions are designed to work with Apache and Nginx web servers, running on Debian and Red Hat-based distributions.

Note
Throughout this guide we will offer several suggested values for specific configuration settings; some of these values will be set by default. These settings are shown in the guide as a reference and you may need to modify them to suit your application accordingly.

Before you Begin

  • When first configuring back-end Linodes, you should set them up according to the instructions in our Getting Started guide. In addition, we recommend that you implement security precautions. For assistance with this, please see our guide on Securing Your Server

  • Generate an SSL certificate for your domain name. This can be done through any Certificate Authority, including Let’s Encrypt using the Certbot tool. Since Certbot cannot run directly on the NodeBalancer, run the following command on any Linode to generate the certificate (after following Certbot’s installation instructions). This allows you to manually verify ownership by updating a DNS record on your domain:

      sudo certbot certonly --manual --preferred-challenges dns
    

    Most Certificate Authorities will generate an SSL certificate using the RSA digital signature algorithm, which is fully supported by NodeBalancers. Certificates using the ECDSA algorithm are not supported.

  • This guide assumes that you have already deployed two or more back-end Linodes and configured them with either a LAMP stack or a LEMP stack. If you have not, please review the following documentation for assistance with configuring your respective stack:

  • In addition, this guide assumes that you have already deployed a NodeBalancer and have configured it with two or more back-end Linodes that make connections on port 80/HTTP. We recommend that you first verify that your NodeBalancer is configured correctly, prior to introducing the complexities of an encrypted connection over SSL. If you would like assistance with setting up a basic NodeBalancer configuration, please review the following documentation:

Note
This guide has been written with the assumption that you are logged in as the root user. If you are using a limited user account, you will need to prefix some commands with sudo.

Install the SSL Certificate and Private Key on your NodeBalancer

  1. On your NodeBalancer Configurations page, select Add another Configuration.

  2. Under Port Configuration, fill out the values in the fields as shown below:

    FieldValue
    Port443
    ProtocolHTTPS
    Session StickinessNone
    SSL CertificatePaste the contents of your SSL certificate. If you have linked multiple segments of a chained certificate, be sure to copy all of its contents into the text field, appearing one after another. The certificate must be signed using the RSA algorithm, which is the default in most cases. ECDSA certificates are not supported.
    Private KeyPaste the contents of your private key. Your private key must not have a passphrase.
    AlgorithmRound Robin
    Health Check TypeHTTP Status
    Interval5
    Timeout3
    Attempts2
    Check HTTP Path/
  3. Select Save Changes when you’re finished.

  4. Add as many nodes as you require for the port configuration by selecting Add a Node. Once selected, fill out the values in the fields as shown below, replacing xxx.xxx.xxx.xxx with your Linode’s private IP address:

    • Label Backend Linode 1
    • IP Address xxx.xxx.xxx.xxx
    • Port 80
    • Weight 100
    • Mode Accept

    Select Save Changes when you’re finished.

Diffie-Hellman Parameters

Diffie-Hellman key exchange is a method for enabling forward secrecy for SSL/TLS connections. Configuring Diffie-Hellman is normally achieved by generating a dhparams.pem file and then updating your web server’s cipher suites list.

A NodeBalancer’s SSL/TLS settings can’t be accessed in the same way you can view your web server configuration, but you can still use Diffie-Hellman with your SSL certificate. This is accomplished by concatenating your certificate file with the contents of your dhparams.pem file and then supplying that to the Certificate field of your NodeBalancer’s HTTPS configuration. The result of this concatenation will look similar to the example:

  -----BEGIN CERTIFICATE-----
YOUR_CERTIFICATE_INFORMATION
-----END CERTIFICATE-----
-----BEGIN DH PARAMETERS-----
YOUR_DHPARAMS_INFORMATION
-----END DH PARAMETERS-----
Caution

To avoid security vulnerabilities, it is recommended that you use at least 2048 bits when generating your Diffie-Hellman parameters:

openssl dhparam -out dhparams.pem 2048

Configure the Apache Web Server

  1. Enable mod_rewrite so that you can redirect all traffic back to the NodeBalancer over port 443/HTTPS:

    a2enmod rewrite
    

    Or, you can load the module manually by appending the following to your Apache configuration file:

    LoadModule rewrite_module modules/mod_rewrite.so
    
    Note

    Depending on your distribution, this file’s location may vary. For example, it can be found at the following paths on Debian and Red Hat based distributions, respectively:

    /etc/apache2/apache2.conf

    /etc/httpd/httpd.conf

  2. Edit the Apache virtual host configuration file to establish the rewrite rules necessary to redirect all incoming traffic from port 80/HTTP back to the NodeBalancer on port 443/HTTPS:

    File: /etc/apache2/sites-available/example.com.conf
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    <VirtualHost *:80>
    
         RewriteEngine    On
         RewriteCond      %{HTTP:X-Forwarded-Proto} !https
         RewriteRule      ^.*$ https://%{SERVER_NAME}%{REQUEST_URI} [L,R=301,NE]
         LogLevel alert rewrite:trace4  # Adjust log verbosity as required. ex. 1-8
     </VirtualHost>

    The rewrite configuration shown above is specific to Apache 2.4 or later. This means that logging gets recorded to Apache’s error.log file. To view only the records specific to mod_rewrite, you can pipe the log file through grep:

    tail -f error_log|fgrep '[rewrite:'
    

    If you are using Apache 2.2, then you will need to replace the LogLevel alert rewrite:trace directive with the following:

    File: /etc/apache2/sites-available/example.com.conf
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    RewriteLog       /var/log/apache2/rewrite.log
    RewriteLogLevel  5  # Adjust log verbosity as required. ex. 1-9
    Caution
    On Red Hat-based distributions, change the Rewritelog path to /var/log/httpd/rewrite.log
  3. Create the RewriteLog as referenced from above:

    • Debian / Ubuntu

        touch /var/log/apache2/rewrite.log
      
    • CentOS

        touch /var/log/httpd/rewrite.log
      

Configure the Nginx Web Server

  1. Edit the Nginx server block configuration file to establish the rewrite rules to redirect all incoming traffic from port 80/HTTP back to the NodeBalancer on port 443/HTTPS:

    File: /etc/nginx/sites-available/example.com.conf
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    server {
        listen   80;
        server_name example.com;
        access_log /var/log/nginx/access.log;
        error_log /var/log/nginx/error.log;
        proxy_set_header X-Forwarded-Proto $scheme;
        location / {
            root   /srv/www/example.com/public_html;
            index  index.html index.htm;
            if ($http_x_forwarded_proto = "http") {
                rewrite  ^/(.*)$  https://example.com/$1 permanent;
                }
            }
        }

    In the above configuration, be sure to replace the values of server_name and root with your actual domain and document root, respectively.

  2. Your configuration should now be complete. After reloading your web server, all requests made to your website that are not sent to port 443 should be redirected back to your NodeBalancer on a secure connection with SSL/TLS.

Tips for Troubleshooting

  • If you have difficulty getting the redirect to work properly or would like to see detailed information about how your SSL certificate is configured, you may wish to utilize the Qualys online SSL Server Test

  • Every time you make changes to your web server’s document root file or other configuration files, be sure to reload the server:

    • For Apache, choose from the following commands, depending on your distribution:

      service apache2 reload
      service httpd reload
      systemctl restart apache2
      systemctl restart httpd
      
    • For Nginx, choose from the following commands, depending on your distribution:

      service nginx reload
      systemctl restart nginx
      
  • When testing behind a load balancer, using curl with the -I or -L flags can be very helpful when debugging:

      curl -I example.com
      curl -L example.com
    

    The -I or --head options will fetch the HTTP-header only. The -L or --location option will detect and display if the server indicates that the requested page has moved to a different location. This option will make curl repeat the request at the new location. If used together with -I, headers from all requested pages will be displayed. This is particularly useful if your rewrite rules have created an infinite loop and your web page does not load. Refer to the man pages for curl for more info.

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