Surviving the Slashdot Effect: High-Performance Caching with Nginx and Varnish

It is 3:00 AM. Your monitoring system is screaming. Your Apache error logs are flooding with server reached MaxClients setting, consider raising the MaxClients setting. You bump it up. Five minutes later, the server swaps to death. Game over.

If you are still serving static assets directly through Apache in 2009, you are doing it wrong. The "C10k problem" (handling 10,000 concurrent connections) isn't solved by throwing more RAM at a prefork MPM. It's solved by architecture.

I have spent the last month migrating a high-traffic news portal in Oslo from a traditional LAMP stack to a high-performance tiered architecture. The results? Load average dropped from 15.0 to 0.4. Here is the exact stack we used, and why your choice of underlying virtualization matters more than your PHP version.

The Architecture: Nginx as the Bouncer, Varnish as the bodyguard

Apache is fantastic at processing PHP, but it is terrible at holding open connections for users on slow mobile networks (like EDGE or 3G). Every open connection eats a thread. Every thread eats RAM.

The fix is a tiered approach:

1. Front-end: Nginx (v0.7.x). It handles thousands of keep-alive connections with a tiny memory footprint.
2. Cache Layer: Varnish (v2.0). It serves hot content from memory before it ever touches the application.
3. Back-end: Apache/PHP. It only works when absolutely necessary.

1. Configuring Nginx as a Reverse Proxy

Don't use Nginx to process PHP via FastCGI unless you enjoy debugging segmentation faults. Use it to buffer the slow clients. Put this in your nginx.conf:

worker_processes 4;
events {
    worker_connections 4096;
    use epoll;
}

http {
    # Buffer slow clients to prevent them from tying up backend resources
    proxy_buffering on;
    proxy_buffer_size 4k;
    proxy_buffers 8 16k;

    upstream backend {
        server 127.0.0.1:8080;
    }
}

The use epoll; directive is critical on Linux kernels (2.6+). It allows O(1) connection handling. If you are on an older VPS provider using outdated kernels, you are capped before you start.

2. Varnish: The "Instant" Button

Varnish 2.0 is the single most effective tool for reducing Time to First Byte (TTFB). By writing a proper VCL (Varnish Configuration Language) file, we can instruct the server to ignore cookies for static content, increasing hit rates dramatically.

Here is a snippet for /etc/varnish/default.vcl that strips cookies from images and static files, ensuring they are always cached:

sub vcl_recv {
    if (req.url ~ "\.(jpg|jpeg|gif|png|ico|css|js)$") {
        unset req.http.cookie;
        return (lookup);
    }
}

sub vcl_fetch {
    if (req.url ~ "\.(jpg|jpeg|gif|png|ico|css|js)$") {
        unset beresp.http.set-cookie;
        set beresp.ttl = 1h;
    }
}

Pro Tip: Always size your malloc storage strictly. If you have 4GB RAM, give Varnish 2GB. Leave the rest for the OS and MySQL. Swapping Varnish pages to disk defeats the purpose.

The Hardware Bottleneck: Why I/O Kills

You can tune software all day, but you cannot code your way out of physics. High-traffic databases generate massive random I/O. Traditional 7.2k SATA drives—or even 15k SAS drives in RAID-5—crumble under this load. The seek times (latency) kill your MySQL queries.

This is where CoolVDS disrupts the market. While most hosts are still overselling spinning rust, CoolVDS is implementing Enterprise SSD storage. The difference in random read/write performance is not incremental; it is exponential.

Database Tuning for SSD

If you are lucky enough to be on an SSD-backed instance, ensure your MySQL my.cnf is tuned to utilize that I/O throughput rather than avoiding it:

[mysqld]
# Set to 70-80% of available RAM on a dedicated DB server
innodb_buffer_pool_size = 1G

# Crucial for data integrity, but on SSDs the penalty is lower
innodb_flush_log_at_trx_commit = 1

# Stop the disk thrashing
innodb_file_per_table = 1

Data Sovereignty and Latency

Performance isn't just about disk speed; it's about the speed of light. If your target audience is in Norway, hosting in Texas is a mistake. You are adding 120ms of latency to every TCP handshake.

Hosting locally in Oslo means you are peering directly at NIX (Norwegian Internet Exchange). Latency drops to 2-5ms. Furthermore, with the Norwegian Personal Data Act (Personopplysningsloven) enforcing strict privacy standards, keeping data within national borders satisfies Datatilsynet requirements better than relying on US Safe Harbor frameworks.

The CoolVDS Implementation

We choose KVM virtualization for our setups. Unlike OpenVZ, which shares the host kernel and often suffers from "noisy neighbor" syndrome, KVM provides true hardware isolation.

When you combine KVM isolation, local NIX peering, and the emerging speed of Solid State storage, you get a platform that doesn't just run your stack—it accelerates it.

Don't let legacy I/O bottlenecks destroy your uptime. Deploy a high-performance KVM instance on CoolVDS today and handle the traffic spike you've been waiting for.