Apache keeps going down after increasing MaxRequestWorkers many times

Symptoms

Apache keeps going down after reaching the MaxRequestWorkers limit even after increasing it multiple times.

server reached MaxRequestWorkers setting, consider raising the MaxRequestWorkers setting

Cause

The limit continues to be reached because of a DDoS attack, or a very long response time for each request.

Resolution

Use the following guides to identify whether the problem is caused by a DDoS attack, or slow response time.

• How to diagnose a DDoS attack
  Based on the results, adjust the firewall and Fail2Ban settings, or disable the affected domain.

• How to enable Apache statistics
  Look for high values in the SS and Req fields; .php scripts that take a long time should have their code reviewed. In the meantime, switching to nginx-only hosting may improve performance.