[
{ type: upgrade
  maximum_version: "3.8.0"
  message: <<EOM
Builtin logger framework log4j-12 has been replaced by Logback at 3.8.0 (ZOOKEEPER-4427).

When upgrading from before 3.8.0 these variables, if used, should be taken into
account:
* zookeeper_log4j_config, zookeeper_rootlogger and zookeeper_log4jpropfile are
  obsoleted for using with Logback.
* zookeeper_logback_config is used instead zookeeper_log4j_config for Logback.
* zookeeper_log4j_config is still used only for log4j-2.
EOM
}
]