High Private Bandwidth & CPU Load on Laravel Servers — Need Help Identifying Root Cause

Question

Hey folks, I’m dealing with a strange performance issue across my Laravel infrastructure and would appreciate expert eyes on this. 🧱 Infrastructure Overview: I have three separate servers on DigitalOcean: Backend Server 2 vCPU, 4GB RAM Laravel app handling: queues, scheduled jobs, email notifications, Laravel Horizon, admin panel Horizon processes ~17,000 jobs/hour on sometimes Frontend Server 4 vCPU, 8GB RAM Laravel + WordPress serving the public web/app interface No cron jobs or queue workers here — it’s just for public traffic Database Server Monitored using DigitalOcean metrics 🧪 Symptoms & Observations: 1. Backend Server Issues CPU usage is constantly 100% even when no jobs are actively processing Horizon dashboard shows idle workers top and ps show multiple php-fpm: pool www processes using 5%+ CPU each Private inbound bandwidth spikes to 100–160 Mbps it happens in sequence, after 5-6 hours. 2. Frontend Server Experiences private outbound bandwidth spikes (same time as backend spikes) No cron jobs, but still shows significant bandwidth usage 3. Database Server Private outbound traffic (to backend) also spikes up to 160+ Mbps Coincides with backend server inbound private bandwidth spikes 🧩 Investigations So Far: Checked Nginx logs: Only minimal legitimate traffic (~5 requests in the past hour from any IP) Detected a research scanner from Ruhr University Bochum hitting .env paths (harmless but noted) No cron jobs or unusual shell processes on the frontend Enabled MySQL slow query log — will monitor if Laravel is overloading DB Laravel log doesn’t show any failed jobs or errors 🧠 My Theory (but unsure) It seems like: The frontend server may be initiating requests to the backend (APIs or queue triggering?) Backend may be doing internal API polling or syncing causing load loops Database is returning large responses, adding to outbound bandwidth and backend CPU load PHP-FPM is stuck in high CPU usage loops possibly because of Laravel jobs or WordPress plugin issues 💭 Questions I’m Stuck On: What could cause such high private traffic between servers if no visible external traffic or jobs are running? Could there be Laravel-to-Laravel internal calls misfiring, especially between frontend and backend? How to trace which requests (internal or external) are causing this load — ideally in real time ? Are there Laravel debugging tools (beyond Telescope) that can help me pinpoint this traffic pattern? I’ve attached Backend Server usage graphs from DO. image alt textBackend Server Usage Graphs from DO image alt textBackend Server Usage Graphs from DO

Bobby Iliev · Answer

Hey!

From the graphs and your notes, it really looks like there’s some kind of internal traffic loop happening between your frontend, backend, and DB, even when things look quiet from the outside.

I’d start by checking your Laravel schedulers with php artisan schedule:list on every server, sometimes the same jobs accidentally run in multiple places. Also worth reviewing any internal API calls between frontend and backend. One small loop or sync job running too frequently can easily cause the kind of spike you’re seeing.

To trace it live, try using iftop or tcpdump on the backend to see exactly what’s coming in over the private network. That’ll help you pinpoint what’s triggering the CPU and bandwidth jumps.

Also, this might be a perfect use case to try out Laravel Nightwatch. It was just released a few days ago, and it can give you insights into background job performance, failed jobs, and scheduling. There’s even a free plan, so you could give it a spin without risk.

And yeah, if PHP-FPM is spiking without jobs running, something might be stuck or retrying silently in the background, Telescope helps, but tools like Blackfire or Nightwatch can show you the full picture.

Let me know what you dig up!

- Bobby