Implementation of remote FS driver based on rsync for libvirt

blueprint remote-fs-driver

Change-Id: Ic975977b620c69e26707c6a6e3402c0b6b1fca73

specs/liberty/approved/implementation-of-remote-fs-driver-based-on-rsync-for-libvirt.rst

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+..
+ This work is licensed under a Creative Commons Attribution 3.0 Unported
+ License.
+
+ http://creativecommons.org/licenses/by/3.0/legalcode
+
+===============================================================
+Implementation of remote FS driver based on rsync for libvirt
+===============================================================
+
+https://blueprints.launchpad.net/nova/+spec/remote-fs-driver
+
+libvirt cannot use RPC to copy files over network to/from other compute nodes.
+That's why libvirt uses additional interface to communicate with other compute
+nodes. Usage of fewer tools for communication between compute nodes can improve
+security, ease of testing and deployment and give better flexibility.
+Right now libvirt driver uses ssh and rsync commands for following operations:
+* creation directory on remote host,
+* creation file on remote host,
+* removing file from remote host,
+* copying file to remote host.
+Target of this BP is implementation of two libvirt remote FS drivers: `ssh` and
+`rsync` drivers. Each of these drivers will implement whole set of operation
+needed by libvirt driver. `ssh` driver will use ssh and scp commands and
+`rsync` driver will use rsync command only.
+
+
+Problem description
+===================
+
+The current libvirt driver uses the following commands for executing remote
+filesystem operations:
+* ssh touch,
+* ssh mkdir,
+* ssh rm,
+* scp,
+* rsync.
+This fact forces us to use an additional shell and this can cause security
+risks. We can not avoid shell usage because copying files over network requires
+a shell. It is possible to decrease the interaction between nodes by using ssh
+commands or rsync commands only. Such separation can allow us to decrease
+number of opened ports on node. Also using only rsync/scp commands can allow
+us to use secure shells like rssh.
+
+Use Cases
+----------
+
+The cloud operator wishes to reduce the number of commands used and the number
+of ports opened by the  nova-compute daemon when migrating workloads between
+compute nodes in order to reduce attack vectors.
+
+Project Priority
+-----------------
+
+None.
+
+Proposed change
+===============
+
+To achieve these goals abstract class 'RemoteFilesystem' will be added in
+nova/virt/libvirt/remotefs.py. This class will contain operations needed for
+libvirt to communicate with other nodes perform filesystem operations on those
+nodes. This abstract class will be implemented in SshRemoteFilesystem and
+RsyncRemoteFilesystem classes.
+Class SshRemoteFilesystem will use ssh and scp tools only(scp uses ssh for data
+transfer, and it uses the same authentication and provides the same security as
+ssh).
+Additional remote FS driver will be implemented in RsyncRemoteFilesystem class.
+This class will use rsync command only.
+Configuration option 'remote_filesystem_transport' will be added with default
+value 'ssh' and 'choices ssh', 'rsync'. Depending on option value corresponding
+class will be instantiated.
+
+Alternatives
+------------
+
+None.
+
+Data model impact
+-----------------
+
+None.
+
+REST API impact
+---------------
+
+None.
+
+Security impact
+---------------
+
+These improvements allow us to decrease number of used ports on compute node.
+Also it allows us to use restricted shell for providing limited access to a
+host like 'rssh'.
+
+Notifications impact
+--------------------
+
+None.
+
+Other end user impact
+---------------------
+
+None.
+
+Performance Impact
+------------------
+
+None.
+
+Other deployer impact
+---------------------
+
+To achieve security benefits some kind of restricted shell must be installed
+on compute nodes. New shell should be used for nova user.
+
+Developer impact
+----------------
+
+None.
+
+
+Implementation
+==============
+
+Assignee(s)
+-----------
+
+Primary assignee: mhorban@mirantis.com
+
+Work Items
+----------
+
+* Implementation of ssh remote FS driver for libvirt.
+* Implementation of rsync remote FS driver for libvirt.
+* Addind configuration option to choose remote FS driver.
+
+
+Dependencies
+============
+
+None.
+
+
+Testing
+=======
+
+tempest test for migration instances will be added.
+
+
+Documentation Impact
+====================
+
+Adding new option 'remote_filesystem_transport' to configure method of compute
+node communication.
+
+
+References
+==========