Hardware and performance

The "untestable" thing is not an issue. It's just that the tests that Moodle includes don't work with Redis. I don't know why. It's always been difficult getting answers out of the people who developed the cache functionality.

Anyway, it doesn't mean that there's a problem.

Hi Andrei,

Performance can be optimized by using caching, caching and caching, for PHP the Zend Opcache, for session and Moodle MUC Redis, for the database InnoDB (load your database in memory). It all fits together when tuned in a way that you find your bottlenecks in your Moodle stack. It took us a lot of time, but we see that every new LTS version asks for a good performance test. Redis 'untestable' means that there is no test configuration found in [your site]/admin/settings.php?section=cachestore_redis_settings, configure it there and you can run the tests. But, as Howard mentioned, it's not a really good test to find out your Redis performance. You could try the Redis benchmark on the server, but that only gives you a view of the server itself, and not when a lot of clients cache their data in Redis. There is a plugin you can install to see some stats of Redis: https://moodle.org/plugins/tool_redis
I hope this gives you a little insight, feel free to contact me if I can help you, as we run almost the same stack.

Hi,

It looks like you’ve done a great job setting up and analyzing your staging and production environments. The fact that your staging setup on Nginx is performing better than production on Apache is a strong indicator that you should consider replicating that setup for production.

1. Is Your Staging Setup Suitable for Production?

Yes, in most cases, Nginx + PHP-FPM performs better than Apache, especially for high-traffic environments like Moodle. Since you have 9,000+ users and a large number of courses, the switch could bring noticeable improvements. However, before making the final decision, you might want to test a few additional aspects:

• Load Testing: Even though staging performs well, running a stress test with simulated high concurrency (e.g., JMeter or Locust) can confirm if it will scale efficiently under real production loads.
• Auto-Scaling Considerations: Since you’re on AWS, it’s worth checking whether your infrastructure should include auto-scaling to handle peak traffic smoothly.
• Load Balancing: If you expect traffic to grow, setting up an Application Load Balancer (ALB) in AWS can help distribute the load evenly.

Once these aspects are verified, transitioning production to Nginx + PHP-FPM should be a good move.

2. Redis "Untestable" Issue – Possible Fixes

If Moodle's built-in performance test is marking Redis as "untestable", the issue could be related to configuration, connectivity, or caching settings. Here are some troubleshooting steps:

Check Redis Connectivity

Run this command on your server:
redis-cli ping
If Redis is working correctly, it should return:
PONG
If not, there may be an issue with the Redis service or its configuration.

Verify Moodle’s Redis Configuration

Make sure your Moodle config.php file includes the correct Redis settings:

$CFG->session_handler_class = '\core\session\redis';
$CFG->session_redis_host = '127.0.0.1'; // Change if using a remote Redis server
$CFG->session_redis_port = 6379;
$CFG->session_redis_database = 0;
$CFG->session_redis_auth = 'your-redis-password'; // If applicable
$CFG->session_redis_acquire_lock_timeout = 120;

Also, check Redis timeouts and memory settings by running:

redis-cli config get timeout
redis-cli config get maxmemory

Use Predis Instead of PHPRedis

Some users have resolved Redis performance issues by switching from PHPRedis to Predis. You can install Predis with:

composer require predis/predis
Then adjust your config.php file accordingly.

Retest Moodle’s Redis Performance

After making these changes, rerun Moodle’s built-in Redis performance test to check if the issue is resolved.

3. Additional Optimizations for High-Performance Moodle Hosting

Since your Moodle instance serves a large number of users, consider the following optimizations:

• Enable a Reverse Proxy (Cloudflare or AWS CloudFront): Helps cache static content and reduce direct server load.
• Fine-Tune MariaDB Settings: Even though MySQLTuner provides recommendations, additional tweaks to InnoDB settings can improve performance. Consider adjustments like:
• innodb_buffer_pool_size = 24G
• innodb_log_file_size = 512M
• innodb_flush_log_at_trx_commit = 2
• query_cache_type = 0
• Upgrade PHP: If possible, test PHP 8.3, as it provides better performance and security improvements.

4. Should You Fully Switch to the Staging Setup?

If your staging environment continues to outperform production under realistic load tests, switching it over makes sense. Just ensure Redis issues are resolved before deploying the changes.
If you are looking for a managed VPS hosting solution optimized for Moodle, you might want to check Onlive Server (https://onliveserver.com/). They offer scalable VPS and dedicated servers that can handle large Moodle installations efficiently, with built-in optimizations for Redis, MariaDB, and PHP-FPM.

Let me know if you need any further insights.