The configuration file can contain comment lines. Comment lines start with a hash (#) or semicolon (;) and continue to the end of the line. Trailing comments are not supported.

Each configuration file consists of a list of configuration sections where each section contains a sequence of configuration options. Each configuration option has a name and value. For example:

[section name]
option = value
option = value
option = value

[section name:optional section key]

option = value
option = value
option = value

A configuration file section header starts with an opening bracket ([) and ends with a closing bracket (]). There can be leading and trailing space characters on the line, which are ignored, but no space inside the section brackets.

The section header inside the brackets consists of a section name and an optional section key that is separated from the section header with a colon (:). The combination of section name and section key is unique for a configuration.

The section names and section keys consist of a sequence of one or more letters, digits, or underscores (_). No other characters are allowed in the section name or section key.

A section is similar to a namespace. For example, the user option's meaning depends on its associated section. A user in the [DEFAULT] section refers to the system user that MySQL Router is run as, which is also controlled by the --user command line option. Unrelated to that is defining user in the [metadata_cache] section, which refers to the MySQL user that accesses a MySQL server's metadata.

The special section name DEFAULT (any case) is used for default values for options. Options not found in a section are looked up in the default section. The default section does not accept a section key.

After a section's start header, there can be a sequence of zero or more option lines where each option line is of the form:

name = value

Any leading or trailing blank characters on the option name or option value are removed before being handled. Option names are case-insensitive. Trailing comments are not supported, so in this example the option routing_strategy is given the value round-robin # Circles back to first server and generates an error when starting the router.

[routing:round-robin]
# Trailing comments are not supported so the following is incorrect
routing_strategy=round-robin # Circles back to first server

Option values support (variable interpolation) using an option name given within braces { and }. Interpolation is done on retrieval of the option value and not when it is read from the configuration file. If a variable is not defined then no substitutions are done and the option value is read literally.

Consider this sample configuration file:

[DEFAULT]
prefix = /usr/

[sample]
bin = {prefix}bin/{name}
lib = {prefix}lib/{name}
name = magic
directory = C:\foo\bar\{3a339172-6898-11e6-8540-9f7b235afb23}

Here the value of bin is "/usr/bin/magic", the value of lib is "/usr/lib/magic", and the value of directory is "C:\foo\bar\{3a339172-6898-11e6-8540-9f7b235afb23}" because a variable named "{3a339172-6898-11e6-8540-9f7b235afb23}" is not defined.

MySQL Router defines predefined variables that are available to the configuration file. Variables use braces, such as {program} for the program predefined variable.

For command-line syntax related information and options, see Section 4.3.1, “Defining Options Using the Command Line”.