Gzip & Brotli Compression: Reducing Transfer Size

Compressing text-based content (HTML, CSS, JS, JSON) reduces network transfer by 60–80% and dramatically improves page load times. Nginx supports both Gzip and Brotli compression.

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Gzip vs Brotli

Item	Gzip	Brotli
Standard	RFC 1952 (1996)	RFC 7932 (2016)
Compression ratio	Baseline	~15–25% better
Speed	Fast	Levels 1–4 are similar; high levels are slower
Browser support	All browsers	Modern browsers (not IE)
Requires HTTPS	No	Browsers only request it over HTTPS
Best use	General purpose	Pre-compressing static files

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Nginx Gzip Configuration

# /etc/nginx/nginx.conf — http block

http {
    # Enable Gzip
    gzip on;

    # Minimum file size (smaller files are not worth compressing)
    gzip_min_length 1024;    # skip files under 1 KB

    # Compression level: 1 (fast, low ratio) – 9 (slow, high ratio)
    # 5–6 is the CPU-efficiency sweet spot
    gzip_comp_level 5;

    # MIME types to compress (images/video are already compressed — skip them)
    gzip_types
        text/plain
        text/css
        text/javascript
        application/javascript
        application/json
        application/xml
        application/rss+xml
        image/svg+xml
        font/ttf
        font/woff
        font/woff2;

    # Compress responses forwarded through a proxy
    gzip_proxied any;

    # Add Vary: Accept-Encoding (helps cache distinguish compressed vs plain)
    gzip_vary on;

    # Disable for IE6 (buggy Gzip support)
    gzip_disable "MSIE [1-6]\.";

    # Compression buffer
    gzip_buffers 32 4k;

    # Apply compression even for HTTP/1.0 requests
    gzip_http_version 1.0;
}

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Nginx Brotli Configuration

Brotli requires a separate module. On Ubuntu install libnginx-mod-http-brotli-filter.

# Ubuntu
sudo apt install libnginx-mod-http-brotli-filter libnginx-mod-http-brotli-static

# Or compile from source
# --add-module=/path/to/ngx_brotli

# /etc/nginx/nginx.conf — http block

http {
    # Dynamic Brotli compression
    brotli on;
    brotli_comp_level 4;      # 0–11, levels 4–6 recommended (CPU efficient)
    brotli_min_length 1024;
    brotli_types
        text/plain
        text/css
        text/javascript
        application/javascript
        application/json
        application/xml
        image/svg+xml;
}

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Pre-compression — Best Performance

For static files, compress at deploy time rather than per-request. This eliminates CPU cost entirely.

# Pre-compress during the deployment pipeline
gzip -9 -k /var/www/html/static/app.js    # creates app.js.gz
brotli -9 -k /var/www/html/static/app.js  # creates app.js.br

# Nginx automatically picks the pre-compressed file
server {
    location ~* \.(css|js|html|json|svg)$ {
        root /var/www/html;

        brotli_static on;  # serve app.js.br if it exists
        gzip_static on;    # serve app.js.gz if it exists
    }
}

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Apache Gzip Configuration (mod_deflate)

# Enable mod_deflate
sudo a2enmod deflate

# /etc/apache2/conf-available/compression.conf
<IfModule mod_deflate.c>
    SetOutputFilter DEFLATE
    DeflateCompressionLevel 5

    AddOutputFilterByType DEFLATE text/html text/css text/javascript
    AddOutputFilterByType DEFLATE application/javascript application/json
    AddOutputFilterByType DEFLATE application/xml image/svg+xml

    # Add Vary header for cache differentiation
    Header append Vary Accept-Encoding

    # Skip already-compressed files
    SetEnvIfNoCase Request_URI \
        \.(?:gif|jpe?g|png|zip|gz|bz2|woff2)$ no-gzip dont-vary

    # Legacy browser handling
    BrowserMatch ^Mozilla/4 gzip-only-text/html
    BrowserMatch ^Mozilla/4\.0[678] no-gzip
    BrowserMatch \bMSIE !no-gzip !gzip-only-text/html
</IfModule>

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Measuring Compression Effectiveness

# Compare size before and after
curl -s -H "Accept-Encoding: gzip" https://example.com/api/products \
    -o /dev/null -w "Size: %{size_download} bytes, Time: %{time_total}s\n"

curl -s https://example.com/api/products \
    -o /dev/null -w "Size: %{size_download} bytes, Time: %{time_total}s\n"

# Check compression headers
curl -I -H "Accept-Encoding: gzip, br" https://example.com/static/app.js
# Content-Encoding: br    ← Brotli in use
# Content-Encoding: gzip  ← Gzip in use

# Measure compression ratio
echo "Original size:"
wc -c /var/www/html/static/app.js

echo "Gzip size:"
gzip -c -9 /var/www/html/static/app.js | wc -c

echo "Brotli size:"
brotli -c -9 /var/www/html/static/app.js | wc -c

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What to Compress — and What to Skip

# DO NOT compress these — already compressed:
# JPEG, PNG, WebP, AVIF — compressed images
# ZIP, GZ, BR, WOFF2   — compressed files
# MP4, WebM             — compressed video
# Encrypted data        — compression has no effect

# DO compress these:
# HTML:      50–70% savings
# CSS:       60–80% savings
# JavaScript: 60–80% savings
# JSON APIs: 60–90% savings (more repetition = better ratio)
# SVG:       70–90% savings (XML-based)

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Performance Tuning Tips

http {
    gzip_comp_level 1;     # Lower level = less CPU for large files
    gzip_min_length 10240; # Only compress files over 10 KB

    # Compress dynamic responses on the fly; serve static with gzip_static
    location /api/ {
        proxy_pass http://backend;
        gzip on;
        gzip_comp_level 5;
    }

    location /static/ {
        root /var/www;
        gzip_static on;   # use pre-compressed files
        brotli_static on;
        expires 1y;
    }
}