When we source the $CONF_ENV_FILE script, we set a few variables which this script expects. Those variables are given without their prefix. For instance, $MNESIA_BASE.
The $CONF_ENV_FILE script can set $RABBITMQ_MNESIA_BASE. Unfortunately before this patch, the variable would be ignored, in favor of the default value which was passed to the script ($MNESIA_BASE).
The reason is that variables set by the script are handled in the alphabetical order. Thus $MNESIA_BASE is handled first, then $RABBITMQ_MNESIA_BASE.
Because the code didn't give any precedence, the first variable set would "win". This explains why users who set $RABBITMQ_MNESIA_BASE in $CONF_ENV_FILE, but using RabbitMQ 3.8.4+ (which introduced rabbit_env), unexpectedly had their node use the default Mnesia base directory.
The patch is rather simple: when we check if a variable is already set, we give precedence to the $RABBITMQ_* prefixed variables. Therefore, if the $CONF_ENV_FILE script sets $RABBITMQ_MNESIA_BASE, this value will be used, regardless of the value of $MNESIA_BASE.
This didn't happen with variables set in the environment (i.e. the environment of rabbitmq-server(8)) because the prefixed variables already had precedence.
michaelklishin
commented
4 years ago
When we source the
$CONF_ENV_FILEscript, we set a few variables which this script expects. Those variables are given without their prefix. For instance,$MNESIA_BASE.The
$CONF_ENV_FILEscript can set$RABBITMQ_MNESIA_BASE. Unfortunately before this patch, the variable would be ignored, in favor of the default value which was passed to the script ($MNESIA_BASE).The reason is that variables set by the script are handled in the alphabetical order. Thus
$MNESIA_BASEis handled first, then$RABBITMQ_MNESIA_BASE.Because the code didn't give any precedence, the first variable set would "win". This explains why users who set
$RABBITMQ_MNESIA_BASEin$CONF_ENV_FILE, but using RabbitMQ 3.8.4+ (which introducedrabbit_env), unexpectedly had their node use the default Mnesia base directory.The patch is rather simple: when we check if a variable is already set, we give precedence to the
$RABBITMQ_*prefixed variables. Therefore, if the$CONF_ENV_FILEscript sets$RABBITMQ_MNESIA_BASE, this value will be used, regardless of the value of$MNESIA_BASE.This didn't happen with variables set in the environment (i.e. the environment of rabbitmq-server(8)) because the prefixed variables already had precedence.
Fixes rabbitmq/rabbitmq-common#401.