Optimizing Apache/LiteSpeed for High-Traffic cPanel Environments: Specific server management Challenges with Concurrency Limits

We provide 'Website Maintenance & cPanel Management Services' and are encountering a persistent performance bottleneck for specific clients on shared/VPS cPanel environments. Despite our diligent server management practices, we're hitting a wall with resource contention.

• Problem Statement: We are experiencing intermittent 503 Service Unavailable errors during moderate traffic spikes, primarily linked to web server (Apache/LiteSpeed) concurrency limits and PHP-FPM pool exhaustion. Standard server management practices for MaxRequestWorkers (Apache), LSAPI_CHILDREN (LiteSpeed), and PHP-FPM pm settings (e.g., pm.max_children, pm.start_servers, pm.min_spare_servers, pm.max_spare_servers) are proving insufficient for dynamic load fluctuations. The errors suggest that processes are not being released or scaled quickly enough to handle the sudden influx of requests.
• Current Configuration: Typically, our VPS setups range from 4-8 vCPU with 8-16GB RAM. We've experimented with various httpd.conf, lsphp.conf, and php-fpm.conf parameters, attempting to balance resource utilization with responsiveness. For instance, increasing pm.max_children often leads to excessive RAM consumption, while conservative settings lead to 503s.
• Seeking Solutions: We are looking for advanced strategies or less common configurations for dynamic resource scaling within cPanel/WHM, especially concerning optimal PHP-FPM process management and its interaction with the web server under varying loads. How can we prevent resource contention and maintain service availability without immediately pushing clients to more expensive dedicated resources? Are there specific kernel-level tunings, alternative PHP-FPM process managers, or web server modules that offer better adaptive scaling for multi-tenant environments?
• Expert Input: We are eager for insights from those who have successfully managed similar high-concurrency, multi-tenant cPanel server management challenges and have found robust solutions that go beyond basic configuration tweaks.

Waiting for an expert reply.