UPD: everything is better now :)

container-files/docker-entrypoint.sh

@@ -1,4 +1,5 @@
 #!/bin/sh
+DEFAULT_LOG_LEVEL="error"
 
 # Disable CustomLog, that is configured by default in upstream.
 sed -i -e 's:^\(\s*\)\(CustomLog\s\s*"logs/access_log"\):\1# Disabled by /docker-entrypoint.sh # \2:' \
@@ -10,7 +11,5 @@ rm -rf /run/httpd/* /tmp/httpd*
 if test "X${SERVER_ADMIN}" != "X" ; then
 	set -- -c "ServerAdmin $SERVER_ADMIN" "$@"
 fi
-if test "X${LOG_LEVEL}" != "X" ; then
-	set -- -c "LogLevel $LOG_LEVEL" "$@"
-fi
+set -- -c "LogLevel ${LOG_LEVEL:-${DEFAULT_LOG_LEVEL}}" "$@"
 exec /usr/sbin/httpd -DFOREGROUND "$@"