Apache vs Lighttpd: The Battle for RAM

It is 2012, and if you are still running a default Apache installation on a 512MB VPS, you are doing it wrong. The web has changed. We aren't just serving static HTML anymore; we are dealing with heavy PHP frameworks, constant AJAX polling, and the looming C10k problem (handling 10,000 concurrent connections).

I recently audited a client's server hosting a popular Norwegian forum. They were plagued by "Error establishing a database connection" during peak hours. The culprit wasn't MySQL. It was Apache spawning so many child processes that the server started swapping to disk. Game over.

Today, we pit the heavy-hitting veteran, Apache HTTP Server, against the lean, event-driven challenger, Lighttpd (Lighty). Which one deserves the CPU cycles on your CoolVDS instance?

The Architecture: Process vs. Event

The fundamental difference lies in how they handle traffic. Understanding this is crucial for tuning.

Apache (The Process/Thread Model)

Apache 2.2 (and the newer 2.4) typically uses the Prefork MPM (Multi-Processing Module) for PHP compatibility. This implies a simple but expensive rule: one request = one process.

If you have 500 concurrent users, you need 500 Apache processes. If each process consumes 25MB of RAM (common with mod_php), you need 12.5GB of RAM just for the web server. On a standard VPS, this leads to thrashing.

Lighttpd (The Event Model)

Lighttpd uses an asynchronous, event-driven architecture. It uses a single process (or very few) and handles I/O events using epoll() on Linux. It doesn't block.

Pro Tip: Lighttpd separates the web server from the PHP interpreter. You run PHP via FastCGI (php-fpm). This allows you to cap the number of PHP processes strictly, while the web server handles thousands of keep-alive connections with a tiny memory footprint.

Configuration Face-Off

Let's look at how we tune these beasts for a high-traffic environment.

Apache Optimization (`httpd.conf`)

If you must use Apache (perhaps for .htaccess support), strictly limit the MaxClients directive to fit your available RAM.

# /etc/httpd/conf/httpd.conf


StartServers       8
MinSpareServers    5
MaxSpareServers   20
ServerLimit      256
MaxClients       256  # Don't set this higher than (Total RAM - DB RAM) / Process Size
MaxRequestsPerChild  4000


# Crucial for performance, but eats RAM in Prefork
KeepAlive On
KeepAliveTimeout 3

Lighttpd Optimization (`lighttpd.conf`)

Here is how we set up Lighttpd to handle high loads using epoll. Note how simple the configuration is compared to the labyrinth of Apache XML-style tags.

# /etc/lighttpd/lighttpd.conf

server.modules = (
    "mod_access",
    "mod_fastcgi",
    "mod_compress",
    "mod_rewrite"
)

# The magic sauce for Linux 2.6 kernels
server.event-handler = "linux-sysepoll"
server.network-backend = "linux-sendfile"

# Connection handling
server.max-fds = 2048
server.max-connections = 1024

# PHP via FastCGI
fastcgi.server = ( ".php" =>
  (( 
    "socket" => "/tmp/php-fastcgi.socket",
    "bin-path" => "/usr/bin/php-cgi",
    "max-procs" => 4,
    "idle-timeout" => 20
  ))
)

Performance Benchmarks

We ran ab (Apache Bench) against a CoolVDS 2GB RAM instance running CentOS 6. The test served a 5KB static file to 1000 concurrent users.

The results are brutal. For static content, Lighttpd obliterates Apache. For dynamic content (PHP), the gap narrows because the bottleneck becomes PHP execution, but Lighttpd still wins on memory overhead.

The Storage Factor: Why SSDs Matter

Regardless of your web server, your bottleneck in 2012 is likely I/O. Apache logging and MySQL writes can choke a standard SATA drive. This is why we deploy CoolVDS instances on Enterprise SSD RAID-10 arrays.

When your web server gets hit with a DDoS or a traffic spike (common if you are linked on Reddit or Digg), the log writes alone can lock up a hard drive. SSDs offer the random I/O performance needed to keep the server responsive while writing logs and reading from the database simultaneously.

Local Context: Hosting in Norway

Performance isn't just about software; it's about physics. If your users are in Oslo or Bergen, hosting on a server in Texas adds 120ms of latency before the first byte is even sent.

Furthermore, we must respect the Personopplysningsloven (Personal Data Act). By keeping your data on servers physically located in Norway, you satisfy the requirements of the Datatilsynet more easily than relying on the US-EU Safe Harbor framework, which is increasingly coming under scrutiny by European privacy advocates.

Verdict: Which one should you choose?

• Choose Apache if: You rely heavily on .htaccess files for rewriting rules, you need specific modules not available elsewhere, or you are on a shared hosting environment where you can't touch the main config.
• Choose Lighttpd if: You have a VPS, you are comfortable editing configuration files, and you need to serve high traffic with limited RAM. It is the pragmatic choice for efficiency.

At CoolVDS, we support both. Our KVM virtualization ensures that if you do choose Apache and it spikes your CPU, it won't be throttled by "noisy neighbors" as often happens with OpenVZ providers. You get the dedicated resources you pay for.

Ready to drop your load times? Don't let your web server wait on spinning rust. Deploy a high-performance SSD VPS with CoolVDS today.