Using Reverse Proxy with Multiple Instances of ODK Central

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Hey everyone!

I wanted to share my experience of setting up multiple instances of ODK Central behind a reverse proxy (Multiple Instances Within Same Docker on a VM is also possible). This setup allows you to efficiently manage and access multiple instances of ODK Central on different virtual machines. Here's a step-by-step guide on how to achieve this configuration.

Prerequisites:

  • ODK Central is installed in a virtual machine (let's call it VM1).
  • You have a main server with internet connectivity that will act as the reverse proxy server.
  • The main server uses Apache as the web server.

Step 1: Installing ODK Central on VM1
Install ODK Central on your virtual machine (VM1) following the standard installation instructions.

Step 2: Configuring Reverse Proxy on the Main Server
On the main server, generate an Apache configuration file (usually saved at /etc/apache2/sites-available). Let's use an example configuration file called mycentral.conf for this demonstration.

Here's an example of the mycentral.conf file:

<VirtualHost *:80>    
    ServerName mycentral.example.com
    ServerAlias www.mycentral.example.com
   
    # Log configuration
    ErrorLog ${APACHE_LOG_DIR}/mycentral_error.log
    CustomLog ${APACHE_LOG_DIR}/mycentral_access.log combined

    ProxyPreserveHost On
    ProxyPass / http://192.168.1.11/
    ProxyPassReverse / http://192.168.1.11/
    
</VirtualHost>

Please note the following:

Step 3: Register SSL Certificate
Before proceeding, ensure that you have registered an SSL certificate for your domain using Let's Encrypt in your main server. You can follow their documentation or use tools like Certbot for the certificate registration process.

Once you have obtained the SSL certificate, add the following line to the mycentral-le-ssl.conf file generated by Certbot (usually saved at /etc/apache2/sites-available):

SSLProxyEngine On

Additionally, modify the http://192.168.1.11/ line in the file to https://192.168.1.11/ to ensure the proxy forwards requests over HTTPS.

The final config file should be like this:

<IfModule mod_ssl.c>
    <VirtualHost *:443>
        SSLProxyEngine On
    
        ServerName mycentral.example.com
        ServerAlias www.mycentral.example.com
   
        # Log configuration
        ErrorLog ${APACHE_LOG_DIR}/mycentral_error.log
        CustomLog ${APACHE_LOG_DIR}/mycentral_access.log combined

        ProxyPreserveHost On
        ProxyPass / https://192.168.1.11/
        ProxyPassReverse / https://192.168.1.11/
    
        Include /etc/letsencrypt/options-ssl-apache.conf
        SSLCertificateFile /etc/letsencrypt/live/mycentral/fullchain.pem
        SSLCertificateKeyFile /etc/letsencrypt/live/mycentral/privkey.pem
    </VirtualHost>
</IfModule>

Step 4: Restart Apache
After making the necessary changes, save the configuration file and restart Apache using the following command:

sudo systemctl restart apache2

Step 5: Accessing ODK Central Instances
With the reverse proxy configured, you can now create and access multiple instances of ODK Central by using different subdomains or URLs that point to the main server. Each subdomain or URL can be associated with a specific ODK Central instance running on it's own VM.

For example, if you have another ODK Central instance installed on a different virtual machine (VM2), you can configure a new virtual host in the mysecondcentral.conf file for that instance using a different subdomain or URL.

That's it! You should now have multiple instances of ODK Central accessible through the main server using a reverse proxy.

If you have any questions or encounter any issues during the setup process, feel free to ask for help in this forum. Good luck!

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