Wednesday, December 22, 2010

Using Amazon EC2 to speed up matlab optimisation I: Writing a socket interface in Matlab to send / receive the commands

The aim in this tutorial (part 1 of 3) is to have a small program running in Matlab on your computer, which will send off requests to a program (compiled Matlab code) running on an Amazon EC2 server or servers.

I am using sockets to do the communication, and in Matlab I use the free msocket toolbox to do this (you will need to download it and add it to your matlab path). The benefit of this toolbox is that it allows you to send matlab variables between machines. In this case, I send a matlab structure containing the command, and the parameters.

The architecture I use is to have a single server running on every core of the target machine. The server will wait for a connection, once it receives one, it will run the desired program, and return the results.

The source code for the entire program can be found here:
socketserver.m. It will also require the program messagecodes.m

It specifies which port to listen on:

socket = mslisten(port);

Then there is a endless loop that waits for a connection

% Keep listening until a connection is received
sock = -1;
while sock == -1
sock = msaccept(socket,0.0000001);

Once a connection has been accepted, a confirmation is returned to the creator:

m.accepted = 1;

and another loop is started to wait to receive commands:

success = -1;
while success<0 [received,success] = msrecv(sock,0.0000001); drawnow; end

I use a "switch" command to execute the appropriate command (in this example,
there is only one, but there is no reason not to have multiple possible commands).

In this case, it is executing the "decompose" command (an optimisation program I have written).
After running, it sends back the result in the rv variable:

switch received.command
case {codes.decompose}
[time,vel,numsubmovements,method,algorithm] = deal(received.arguments{:});
[,rv.bestresult,rv.bestfitresult] = ...

Once a client has finished running the program, it can close the socket, which is dealt
with by the server as follows:

case {codes.closesocket}

The break causes it to leave the innermost while loop, and wait again for a new connection.

In order to use this code on Amazon EC2 (without a license server), it is necessary to first compile it. You will need to have a license for the Matlab compiler (available on the
computer doing the compiling, but not on the one running the final program). Note that you will
need to compile this on a machine similar to the one you are planning on running it on
(e.g., I compiled mine on a 64-bit ubuntu machine). I installed ubuntu as a Virtualbox
image as I don't have a "real" ubuntu machine available.

Then from inside matlab, it is as simple as to run:

mcc -m socket_server

and matlab will compile it for you. If this is the first time using mcc, you may
have to answer some questions. Part 3 described how to upload this server to EC2.

Now for the client. The client has to connect to the server:

sock = msconnect(address,port);

It then can send commands to the server:

m.command = codes.decompose;
m.arguments{1} = time;
m.arguments{2} = vel;
m.arguments{3} = numsubmovements;
m.arguments{4} = method;
m.arguments{5} = algorithm;
success = mssend(sock,m);

It then needs to wait for a result:

[thisrv,success] = msrecv(sock);

Then the return value can be used as desired.

Part 2 continues by explaining how to setup Amazon EC2 to run the server component.

Part 3 of the tutorial will describe an automated way to run many servers and collect the results.


  1. I'm trying to adapt this solution to be deployed on my universities super computer.

    When I try to run this as compiled code I get an error saying mlisten is undefined. I realize this is part of the msocket toolbox you mentioned, which I have downloaded. To make this work do I have to use the matlab compiler to compile all of the msocket code individually? Or is there an easier way to make this work?

    1. Yes, it sounds like you will need to compile mex files for your computer (probably linux). This is easy to do, the msocket toolbox comes with a script "compileit" which will do this for you.

  2. Hi Jason, thanks for the tutorial.
    I am a new user of Matlab and the ec2. Do you install a matlab on the Amazon ec2 to run your compiled code?

    1. No, you don't need to install Matlab, but you do need to install the Matlab MCR (which you can put on another computer without needing another license). The details of how to install it are in part two of the tutorial, about half way down:

    2. Thanks for your reply Jason.

      I went through the second part of the tutorial, and found that you used a bunch of command to install the software on the instance. I am a little bit confused that what are those codes and is it like the windows command?

      By the way, I launched a windows server instance, followed the instruction, I have already connected to the instance and logged in as administrator. Is that necessary to use the puTTY?

      Thanks a lot.

    3. When you start the instance, it does not have any of the matlab or other software we need. So first we need to install these on the instance. Rather than opening a graphical interface, we issue the commands through the command line.

      It does not matter which program you use, if you can connect to the instance.

  3. Jason would you be kind enough to highlight the basic changes that i will have to make to adapt this solution to Windows Azure Cloud?

    1. Sorry, I don't have any experience using Windows Azure Cloud. But parts 1 + 3 of the tutorial should be identical. You will need to work out how to setup a "virtual machine" in azure, but there are ubuntu ones available, similar to the process I described here using EC2.