Static File Serving Optimization

Nginx's ability to serve static files quickly is a cornerstone of web performance. Correctly configuring expires, Cache-Control, sendfile, and gzip can dramatically improve client load times.

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sendfile — Kernel-Level File Transfer

Standard file transfer reads file contents into user space and then sends them to the socket. Enabling sendfile transfers files directly from the kernel to the socket, reducing memory copies and CPU overhead.

[Standard]
Disk → Kernel buffer → User space → Socket buffer → Network
             (2 memory copies)

[sendfile]
Disk → Kernel buffer → Socket buffer → Network
         (processed entirely in kernel, 1 copy)

http {
    sendfile        on;    # Use sendfile() syscall
    tcp_nopush      on;    # With sendfile: bundle TCP packets to max size
    tcp_nodelay     on;    # Send last packet immediately without delay
}

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Cache Control (expires, Cache-Control)

Proper browser caching reduces unnecessary server requests from repeat visitors, lowering both traffic and response times.

expires Directive

server {
    root /var/www/html;

    location ~* \.(png|jpg|jpeg|gif|webp|svg|ico)$ {
        expires 7d;
    }

    location ~* \.(woff|woff2|ttf|otf|eot)$ {
        expires 1y;
    }

    # JS/CSS with build hash — 1 year (immutable)
    location ~* \.(js|css)$ {
        expires 1y;
        add_header Cache-Control "public, immutable";
    }

    # HTML — no cache (always fetch latest)
    location ~* \.html$ {
        expires -1;
        add_header Cache-Control "no-store, no-cache, must-revalidate";
    }
}

Cache-Control Header Values

Value	Description
public	Allow CDN and intermediate caches
private	Browser cache only, no CDN caching
no-cache	Store cache but revalidate with server before use
no-store	Do not store cache at all (sensitive data)
must-revalidate	Expired cache must be revalidated with server
immutable	Content will never change during cache validity
max-age=N	Cache valid for N seconds

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Gzip Compression

Compressing text-based files before sending can reduce network traffic by 50–80%.

http {
    gzip  on;
    gzip_comp_level  6;          # Level 1–9 (6 balances speed vs ratio)
    gzip_min_length  1024;       # Don't compress files smaller than 1KB
    gzip_http_version  1.0;
    gzip_vary  on;               # Vary header for proxy caching

    gzip_types
        text/plain
        text/css
        text/javascript
        text/xml
        application/javascript
        application/x-javascript
        application/json
        application/xml
        application/xml+rss
        image/svg+xml
        font/woff
        font/woff2;
}

Verify Gzip

# Check for Content-Encoding: gzip header
curl -H "Accept-Encoding: gzip" -I http://example.com/app.js

# Should see:
# Content-Encoding: gzip
# Vary: Accept-Encoding

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Open File Cache — File Descriptor Caching

Reduce the number of open() syscalls in high-traffic static file environments by caching file descriptors.

http {
    open_file_cache  max=1000 inactive=20s;
    open_file_cache_valid  30s;
    open_file_cache_min_uses  2;
    open_file_cache_errors  on;
}

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Comprehensive Static Serving Configuration

Production-ready static file serving optimization:

server {
    listen 80;
    server_name static.example.com;
    root /var/www/static;

    open_file_cache max=5000 inactive=20s;
    open_file_cache_valid 30s;
    open_file_cache_min_uses 2;
    open_file_cache_errors on;

    # Versioned/hashed assets — 1 year strong cache
    location ~* \.[0-9a-f]{8,}\.(js|css)$ {
        expires 1y;
        add_header Cache-Control "public, immutable";
        access_log off;
    }

    # Images and fonts — 30 day cache
    location ~* \.(png|jpg|jpeg|gif|webp|ico|svg|woff|woff2|ttf)$ {
        expires 30d;
        add_header Cache-Control "public";
        access_log off;
    }

    # HTML — no-cache
    location ~* \.html$ {
        add_header Cache-Control "no-cache";
    }

    location / {
        try_files $uri $uri/ =404;
        expires 7d;
        add_header Cache-Control "public";
    }
}

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Summary

Optimization	Setting	Effect
sendfile on	Kernel direct transfer	Reduced CPU usage, higher throughput
tcp_nopush on	Bundle TCP packets	Improved network efficiency
expires	Browser cache duration	Fewer requests from repeat visitors
Cache-Control: immutable	Strong cache (no changes guaranteed)	Eliminates unnecessary revalidation
gzip on	Text compression	50–80% reduction in transfer size
open_file_cache	File descriptor caching	Fewer I/O syscalls