oracular (1) nginx-confgen.1.gz
NAME
nginx-confgen - A preprocessor and macro system for nginx(-like) configuration files.
SYNOPSIS
nginx-confgen -i input.conf -o output.conf
DESCRIPTION
nginx-confgen can be used to do pre-processing for nginx configuration files (and other configuration
files with a similar syntax). It has support for "compile-time" macro expansion and variable
interpolation, which should make it less tedious to maintain large and complex configurations.
nginx-confgen works by parsing the input into a syntax tree, modifying this tree, and then formatting the
tree to generate the output. It is completely oblivious to nginx contexts and directives, so it is
possible to do nonsensical transformations and generate incorrect configuration files. Comments in the
input file will not be present in the output. See also the "BUGS & WARTS" below.
SECURITY CONSIDERATION: Do NOT use nginx-confgen with untrusted input, the "pre_exec" directive allows
arbitrary code execution by design.
OPTIONS
The following command-line options are supported:
-h Show help text.
-V, --version
Show program version.
-i FILE
Use the given file name as input file. If this option is not given or set to "-", then the file will
be read from standard input.
-o FILE
Write the output to the given file. If this option is not given or set to "-", then the file will be
written to standard output.
-I DIR
Set the search path for pre_include directives. This option can be given multiple times to search
several directories in order. If this option is not given, then include files are resolved relative
to the directory that nginx-confgen is run from (i.e. "-I .").
DIRECTIVES
nginx-confgen recognizes and interprets the following directives:
pre_include
Similar to the "include" directive in nginx, except that the file is included during preprocessing. The
included file may contain any preprocessing directives supported by nginx-confgen. Variables and macros
defined in the included file will be available in the parent file.
Relative paths are searched for in the directories given with the "-I" flag.
pre_set
Similar to the "set" directive in nginx, except that variables defined with "pre_set" are resolved during
preprocessing. Variables are set in the order that they are encountered in the configuration file,
regardless of scoping. For example:
pre_set $var outer;
location / {
pre_set $var inner;
}
# $var is "inner" at this point.
Only variables that are known to nginx-confgen will be substituted, unknown variables are assumed to be
run-time variables for nginx and will be left alone without warning. For example:
pre_set $ip 127.0.0.1;
deny $ip; # This will output as: deny 127.0.0.1;
deny $otherip; # This will output as: deny $otherip;
pre_exec
Run a shell command and store the output in a variable. For example, nginx will not use your system's DNS
resolution methods to resolve domain names, instead you need to manually set a "resolver" address. With
the following hack you can fetch the nameserver from "/etc/resolv.conf" and use that as the "resolver":
pre_exec $nameserver "grep nameserver /etc/resolv.conf \\
| head -n 1 | sed 's/^nameserver //'";
resolver $nameserver;
(The "\\" is necessary, otherwise your shell will consider the newline as a new command).
pre_if
Similar to the "if" directive in nginx, except that this is evaluated during preprocessing. Braces around
the condition are optional. Some examples:
pre_if -f $certdir/ocsp.der {
ssl_stapling on;
ssl_stapling_file $certdir/ocsp.der;
}
pre_if (!-f $certdir/ocsp.der) {
ssl_stapling off;
}
# You can have different configuration depending on the name of
# the system on which nginx-confgen runs. Like... yeah.
pre_exec $hostname 'hostname';
pre_if $hostname ~* ^proxy_for_(.+) {
proxy_pass http://$1/;
}
pre_warn
This directive, when interpreted, will generate a warning to the standard error of nginx-confgen. Can be
used to signal that a special configuration is being used:
pre_if -e /etc/offline-mode {
pre_warn "Putting website in offline mode!";
}
Or to warn about certain directives:
pre_macro proxy_cache $var {
pre_warn "Using proxy_cache with $var violates company policy!";
# But we can output it anyway.
proxy_cache $var;
}
macro
Define a macro, which is a configuration block that you can later refer to. The general syntax is as
follows:
macro macro_name $var1 $var2 @remaining_vars &block_var {
# contents
}
The optional @remaining_vars argument will capture any number of variables and can be passed to another
directive inside the macro contents. The optional &block_var allows the macro to be invoked with a block
argument, which will expand to any number of directives. Some examples:
macro le {
location /.well-known/acme-challenge {
alias /etc/letsencrypt/challenge;
}
}
# Usage:
le;
macro redir $path $to {
location $path {
return 301 $to;
}
}
# Usage:
redir / http://blicky.net/;
macro vhost $primary_name @aliases &block {
server {
listen [::]:443 ssl;
server_name $primary_name @aliases;
ssl_certificate $crtdir/$primary_name/fullchain.pem;
ssl_certificate_key $crtdir/$primary_name/privkey.pem;
█
}
}
# Usage:
vhost example.com {
root /var/www/example.com;
}
vhost example.org alias.example.org {
root /var/www/example.org;
}
Note that these are hygienic macros, so variable capture is predictable (but not necessarily the most
useful):
pre_var $dest /a;
macro redir {
# This will be /a, regardless of the context in which this macro is called.
return 301 $dest;
}
# $dest is still '/a' inside the macro after this new variable definition.
pre_var $dest /b;
redir;
Similarly, macro arguments will not be available inside &block expansion or nested macro expansion and
any variables set inside a macro will not be available outside of the macro body.
BUGS & WARTS
nginx-confgen is a quickly written hack to solve a particular use case, it is quite likely to have some
weird behavior and bugs. In particular, processing performance may suffer on large configuration files
with many macros and/or variables. Performance has simply not been a problem for me, but if you do run
into trouble with your use case, let me know so I can fix it.
Comments and whitespace in the input files are thrown away and ignored. The generated output is
completely reformatted.
The nginx configuration syntax is not as regular as I had hoped. It's possible for nginx modules to
extend the syntax somewhat. A good example is the types directive in ngx_http_core_module. While nginx-
confgen should be able to handle the types directive just fine, other extensions may cause syntax errors
or will not survive a round-trip through nginx-confgen. This applies to all *_by_lua_block directives in
the ngx_http_lua_module. The _by_lua directives that accept a string should work just fine.
AUTHOR
nginx-confgen is written by Yoran Heling <projects@yorhel.nl> Web: <https://dev.yorhel.nl/nginx-confgen>