环境变量

HAProxy's configuration supports environment variables. Those variables are interpreted only within double quotes. Variables are expanded during the configuration parsing. Variable names must be preceded by a dollar ("$") and optionally enclosed with braces ("{}") similarly to what is done in Bourne shell. Variable names can contain alphanumerical characters or the character underscore ("_") but should not start with a digit.

举例:

bind "fd@${FD_APP1}"
log "${LOCAL_SYSLOG}:514" local0 notice   
# send to local server
user "$HAPROXY_USER"