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==========
Lantorrent
==========
Lantorrent is a file distribution protocol integrated into the Nimbus
IaaS toolkit. It works as a means to multi-cast virtual machine images
to many backend nodes. The protocol is optimized for propagating
virtual machine images (typically large files) from a central repository
across a LAN to many virtual machine monitor nodes.
Lantorrent works best for the following scenarios:
1) large file transfers (VM images are typically measured in gigabytes)
2) local area switched network (typical for data center computer racks)
3) file recipients are willing peers.
4) many endpoints request the same file at roughly the same time
-----------------
Protocol overview
-----------------
When an endpoint wants a file it submits a request to a central agent.
This agent aggregates request for files so that they can be sent out in
an efficient single multi-cast session. Each request for a source file
is stored until either N request on that file have been made or N'
seconds have passed since the last request on that source file has been
made. This allows for a user to request a single file in several
unrelated session yet still have the file transfered in an efficient
multi-cast session.
Once N requests for a given source file have been made or N' seconds
have passed the destination set for the source file is determined. A
chain of destination endpoints is formed such that each node receives
from and sends to one other node. The first node receives from the
repository and send to a peer node, that peer node sends to another,
and so on until all receive the file. In this way all links of the
switch are utilized to send directly to another endpoint in the switch.
This results in the most efficient transfer on a LAN switched network.
Often times in a IaaS system a single network endpoint (VMM) will want
multiple copies of the same file. Each file is booted as a virtual
machine and that virtual machine will make distinct changes to that file
as it runs, thus it needs its own copy of the file. However that file
does not need to be transfered across the network more than once.
Lantorrent will send the file to each endpoint once and instruct that
endpoint to write it to multiple files if needed.
-----------------------------
Enabling Lantorrent in Nimbus
-----------------------------
Lan torrent is part of the Nimbus distribution as of Nimbus 2.6.
However, due to system administrative overhead it is not enabled by
default. To enable Lantorrent in Nimbus there are a few configurations
changes that must be made.
The following software is required on both service and VMM nodes:
- python 2.5
- python simplejson
Lantorrent is run out of xinetd thus it must also be installed on all VMMs.
To install LANTorrent you must take the following steps:
1) edit $NIMBUS_HOME/nimbus-setup.conf
change lantorrent.enabled: False -> lantorrent.enabled: True
2) edit $NIMBUS_HOME/services/etc/nimbus/workspace-service/other/common.conf
change the value of propagate.extraargs:
propagate.extraargs=$NIMBUS_HOME/lantorrent/bin/lt-request
be sure to expand $NIMBUS_HOME to its full and actual path.
3) install lantorrent on VMM
- run ./vmm-install.sh on each node
either run it as your workspace control user or specify the workspace
control user as the first and only argument to the script.
4) install lantorrent into xinetd
- the vmm-install.sh script creates the file lantorrent. This
file is ready to be copied into /etc/xinetd.d/. Once this is done
restart xinetd (/etc/init.d/xinetd restart).
5) change the propagation method.
- edit the file:
$NIMBUS_HOME/services/etc/nimbus/workspace-service/other/authz-callout-ACTIVE.xml
and change:
<property name="repoScheme" value="scp" />
to:
<property name="repoScheme" value="lantorrent" />
6) restart the service: $NIMBUS_HOME/bin/nimbusctl restart
7) [optional] if the path to Nimbus on the workspace control nodes (VMMs)
is not /opt/nimbus you will also need to edit a configuration file on
all backends.
In the file:
<workspace control path>/control/etc/workspace-control/propagation.conf
make sure the value of:
lantorrentexe: /opt/nimbus/bin/ltclient.sh
points to the proper location of you ltclient.sh script. This should
be a simple matter of changing /opt/nimbus to the path where you chose
to install workspace control.
----------------
Protocol details
----------------
requests
--------
transfer
--------
A transfer from one peer to another is performed for forming a TCP
connection. A json header is first sent down the socket describing the
transfer. It describes the files where data must be written, and the
other endpoints where the data must be sent. As data comes in the
server will store it to one or more files and forward it on to another
endpoint. All of this information is contained in the header. The
header has the following format:
{
host
port
length
requests = [ {filename, id, rename}, ]
destinations =
[ {
host
port
requests = [ { filename, id, rename } ]
block_size
}, ]
}
When the server forms a connection with the next endpoint it will form
another header by removing the first entry of the destination list and
using the values contained in it as root level values in the header
described above. If the destination list is empty then the server is the
last in the chain and no forwarding is needed.
After the header is sent the binary payload (the contents of the file)
is sent down the socket.
The 'requests' value of the json header contains destination
information. Each filename in the list is a file where data should be
written. The value of id is the id of the request for that file. The
value of rename is a boolean which determines if the file should be
first written to a temporary location and then moved to the final
location once all of the data is received. This feature is helpful in
monitoring file completion.
security
--------
Each connection to a lantorrent peer comes with a json header. Directly
following that header is a line of text in the following format:
EOH : <signature>
The value of signature is the hmac signature of everything that came
before the literal EOH. The password for that signature is found in the
lt.ini file. Every endpoint and the master repo must have the same
value for that password.
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