mod_deflate (since lighttpd 1.4.42) enables output compression of responses. (Content-Encoding)

Output compression reduces the network load and can improve the overall throughput of the webserver. All major http-clients support compression by announcing it in the Accept-Encoding header. This is used to negotiate the most suitable compression method. We support deflate, gzip, bzip2, brotli (since 1.4.56), and zstd (since 1.4.59).

deflate (RFC1950, RFC1951) and gzip (RFC1952) depend on zlib.
brotli (RFC7932) is supported in most popular browsers.
zstd (RFC8478)
bzip2 is only supported by lynx and some other console text-browsers, and is no longer recommended; brotli or gzip should be preferred.

Since lighttpd 1.4.56, mod_deflate subsumes and replaces mod_compress. mod_deflate can compress static and dynamic responses, while mod_compress could compress only static files.

Module options:

#deflate.mimetypes = ("text/")       # prefix matches all text/* Content-Type responses
deflate.mimetypes = ("text/html", "text/plain", "text/css", "text/javascript", "text/xml")
deflate.allowed-encodings = ( "br", "gzip", "deflate" ) # "bzip2" and "zstd" also supported

## optional

deflate.cache-dir = "/path/to/compress/cache" 

#deflate.max-compress-size = 131072   # measured in kilobytes, so 131072 indicates 128 MB
#deflate.min-compress-size = 256      # measured in bytes
#deflate.max-loadavg = "3.50" 

#deflate.params = (                   # since lighttpd 1.4.60 (recommended: leave defaults unless you test your changes for positive effect)
#  "BROTLI_PARAM_QUALITY"    => 4,    #  0..11 (default is  4 (not 11 (BROTLI_DEFAULT_QUALITY) due to time costs of BROTLI_DEFAULT_QUALITY))
#  "BROTLI_PARAM_LGWIN"      => 22,   # 10..24 (default is 22 (BROTLI_DEFAULT_WINDOW))
#  "BROTLI_PARAM_MODE"       => 0,    #  0..2  (default is  0 (BROTLI_MODE_GENERIC)) (1: BROTLI_MODE_TEXT) (2: BROTLI_MODE_FONT)
#  "ZSTD_c_compressionLevel" => 3,    # -3..22 (default is  3 (ZSTD_CLEVEL_DEFAULT)
#  "ZSTD_c_strategy"         => 0,    #  1..9  (default is  0 (use zstd default strategy))
#  "ZSTD_c_windowLog"        => 0,    # 10..31 (default is  0 (use zstd default windowLog))
#  "gzip.level"              => 6,    #  1..9  (default is  6 (Z_DEFAULT_COMPRESSION))
#  "gzip.windowBits"         => 6,    #  9..15 (default is 15 (MAX_WBITS))
#  "gzip.memLevel"           => 8,    #  1..9  (default is  8 )
#  "gzip.strategy"           => 0,    #  0..4  (default is  0 (Z_DEFAULT_STRATEGY)) (1: Z_FILTERED 2: Z_HUFFMAN_ONLY 3: Z_RLE 4: Z_FIXED)
#  "bzip2.blockSize100k"     => 9,    #  1..9  (default is  9 (block size 900k))

#deflate.compression-level = 9        # deprecated; overloaded; use deflate.params (since 1.4.60) for encoder-specific values) = 2048       # deprecated; gzip-specific; currently has no effect (unused) in code
#deflate.output-buffer-size = 8192    # deprecated; gzip- and bzip2-specific; currently has little effect in code (due to mod_deflate not streaming partial responses)

deflate.cache-dir (since 1.4.56) is the location under which to store cache of compressed files. Cleaning the cache is left to the user. A cron job deleting files older than
10 days could do it: find /path/to/compress/cache -type f -mtime +10 | xargs -r rm

deflate.allowed-encodings lists the encodings from which the server will select. Since lighttpd 1.4.60, the ordering of this list is preserved and the server selects the first encoding from this list which matches a value in the client request Accept header.

deflate.max-compress-size is the largest response size that will be compressed.
deflate.min-compress-size is the smallest response size that will be compressed.
deflate.max-loadavg is max system loadavg before bypassing compression (since 1.4.43)

deflate.params configures encoder-specific tunables. It is strongly recommended to omit deflate.params and to use lighttpd defaults unless you test your changes for positive effect. (FYI: the parameters are named to directly map to the names in the C headers of the encoder libraries)

deflate.compression-level (deprecated) is compression level or quality tuning for the underlying compressor. (deprecated; use deflate.params (since 1.4.60) for encoder-specific values)
(more info: man gzip (1..9); man bzip2 (1..9); man -s 3brotli encode.h (0..11)

Known Limitations

mod_deflate currently does not stream compressed content in chunks. This affects very large dynamic responses, or dynamic responses sent in chunks with large time lapses between chunks. If the entire response is not ready when the response header is sent, mod_deflate does not compress the response. (e.g. dynamic response from backend and is set > 0) While mod_deflate does not handle this use case, the backend producing the streaming response is able to apply an appropriate Content-Encoding itself (instead of mod_deflate).

mod_deflate deflate.cache-dir, if set, contains cached output of static files, but does not cache dynamic responses unless the response contains an ETag response header. (dynamic responses, if eligible, are still compressed by mod_deflate before the response is sent to the client.)

mod_deflate must be listed after mod_setenv in server.modules if mod_setenv might be used to force setting "Content-Encoding" response header.


For selection/negotiation of pre-compressed files in the document root, e.g. or main.html.gz when main.html is requested, use mod_magnet with custom lua code for Content-Negotiation

Updated by gstrauss about 1 month ago · 40 revisions