Implementation of remote FS driver based on rsync for libvirt

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

Creative Commons Attribution 3.0 License

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nova-specs