Hi, Want to initiate a discussion here. Before Mesos containerizer has container image support (all containers share the same host file system), $MESOS_DIRECTORY env variable is used to let executor know their sandbox location.
Later, we introduced container image support to Mesos containerizer so that each container can has its own root filesystem. Due to some historical reason (thermos), we decided to keep $MESOS_DIRECTORY to be the path to the sandbox on the host filesystem (e.g., `/var/lib/mesos/slaves/...`) even if the container has its own root filesystem. And introduced a new $MESOS_SANDBOX to point to the sandbox in the container's root filesystem (e.g., `/mnt/mesos/sandbox`). If the container does not have a root filesystem, $MESOS_DIRECTORY == $MESOS_SANDBOX. Now, we plan to deprecate $MESOS_DIRECTORY because it'll be really confusing to executor writers, and it'll be an error if they try to access $MESOS_DIRECTORY if their container has a root filesystem defined. - Jie
