Machine Callback Design

The Problem

Being able to remotely execute commands on stateless executors. The problem is that the controller does not know how to connect to the executor. Such a situation could be when a VM is started, and the hypervisor is unable to detect its IP information, or when the VM is behind a firewall, so the controller cannot access the executor directly.

To make things a bit more easier, let me define some things for the rest of the document:

executor:	The virtual machine that will execute the code
controller:	The machine that orchestrates the whole process

There is a 1:1 relationship between the controller instance and the executor instance

Step 1 - Create Configuration

On the controller, some files and settings need to exist:

• generate CONTROLLER_KEY
• allocate two ports on the system: CONTROLLER_PORT and CALLBACK_PORT. CONTROLLER_PORT has to be free on localhost, CALLBACK_PORT needs to be available on an externally accessible IP.

Step 2 - Create AFTER_INSTALL Script for the Specific Distribution

This script's responsibilities are:

• Configure the new system, so that eth0 will work with DHCP
• Configure a CALLBACK service on the new system, that will be executed on each boot, and will:
• Establish an SSH connection to the controller's IP address, with a specific CALLBACK_USER on a specific CALLBACK_PORT with a specific CALLBACK_KEY and forward it's ssh to a CONTROLLER_PORT
• Authenticate CONTROLLER_KEY for CONTROLLER_USER
• Shut down the machine

Step 3 - Create an Install Media

To install an operating system on a VM using some virtualisation platform. I think the Greatest Common Divisior of virtualisation platforms that I know so far is an ISO file. The project unattended-ubuntu-iso creates an ISO that will install Ubuntu, and shut down afterwards. It is also possible to inject a custom AFTER_INSTALL script. The installer should also create CONTROLLER_USER.

Step 4 - Install Operating System

A VM has to be created with a virtual hard drive, and a virtual cdrom - with the Install Media inserted. At this point the VM does not need network connection. It only uses the CDROM. The created VM has to be started, and have to wait until it's halted. The AFTER_INSTALL script will perform the specified steps, and shut the VM down.

Step 5 - Start a Controller

On the controller, an ssh server has to be started, allowing CALLBACK_USER to connect with CALLBACK_KEY.

Step 6 - Save the Image

The installer VM that was used to run the install process can be destroyed, only the hard disk needs to be kept - this is the image.

Step 7 - Start a new Instance

With the image created in the previous step, the executor could be created. This time it needs network connection as well. The virtualisation platform has to start the executor. As the AFTER_INSTALL script has already configured the networking, the executor will be configured by DHCP. As the executor started, it will start the CALLBACK script, which will establish a secure channel on CONTROLLER_PORT.

Step 8 - Execute commands

The controller can now access the executor's ssh server on the CONTROLLER_PORT. It will use CONTROLLER_USER and CONTROLLER_KEY to execute commands on the remote machine.

Git review

Just a quick note. If you are reviewing the changes in a git repository, the following command might be useful:

git log -p --color

This gives you a nice, colored diff.

Weekend

This weekend started with friday. I took a day off to relax my mind. This relaxation ended up sitting in front of my laptop, experimenting wit vsphere's opensource java api, while trying to build an embedded vm that can run java - just with buildroot. On saturday, I managed to find out, what osgi is, and I think it will be a useful ground for running java bundles on my emvms (embedded vms). The same day I learned, that a proper libc is needed, so I experimented with the linux kernel - crosstool-ng - buildroot trinity. On sunday we went to cinema to watch the rather old movie: gravity, re done and posted yesterday's build efforts with some extra deployment script, and closed the day with some control theory, learning about zenos, and how to deal with type 1 zenos. Good night.

First post from phone

This is my first post created with my phone. The picture shows a thermapen, we used it during the weekend.

VM From Scratch

I have spent a lot of time installing various Linux distributions, automating all the complex things, trying out things like puppet, writing my own management scripts. Well, in the end of the day, the goal was to run a very simple application. Usually these applications run inside a hypervisor, and we don't really want to spend time with the operating system's management. All I want is a Virtual Machine that has my application and I don't want to know more about it. I think I'm even not interested in sshing into that box. I want to build VMs quickly.

There are several tools to build a VM, and I believe all do their job perfectly. But I think it's time for me to try to build a VM from scratch. The components, that I will use are:

• linux
• crosstool-ng
• buildroot

Getting the kernel

At the time of writing the linux version that I picked, is 3.10.32 - I believe, it has a long term support. So let's dive in, and get the source code

cd /data/matelakat/kernel
wget https://www.kernel.org/pub/linux/kernel/v3.x/linux-3.10.32.tar.xz
tar -xJf linux-3.10.32.tar.xz

Now that we have the sources, we can create a cross compiler.

crosstool-ng

This tool will help me to build a cross compiler. At the initial phase, my target architecture is 686 32bit. I picked this one, as I would like to test the VM with nested virtualization (ESXi inside VirtualBox), and you can't run 64 bit guests there. So let's get started:

first, download the tools, and check out a specific revision. This makes it easier for anyone to reproduce.

mkdir /data/matelakat/xtool
cd /data/matelakat/xtool
hg clone http://crosstool-ng.org/hg/crosstool-ng
cd crosstool-ng/
hg checkout 9321d9d7af9b

Now comes the crosstool-ng specific part. First, we need to actually install crosstool-ng:

./bootstrap
./configure --prefix=$(cd .. && pwd)/ctng
make
make install
export PATH=$PATH:$(cd .. && pwd)/ctng/bin

The next step is to generate a configuration for the crosstool. I will start by getting a sample configuration file, and overwriting it with my config:

cd /data/matelakat/xtool/
mkdir configuration
cd configuration/
ct-ng x86_64-unknown-linux-gnu
cp /data/matelakat/vmfromscratch/crosstool-ng/.config .config
ct-ng menuconfig

If you are happy with the config, it's time to build the cross compiler. My config will put the downloaded sources and the built tools to ../src and ../x-tools, so I need to create those directories in advance. Also, as I have a laptop with 4 cores, I will use 6 jobs simultaneously:

mkdir ../src ../x-tools
time ct-ng build.6

I can definitely tell: my CPU cores are busy - some hot air flows out of my good old Lenovo R500. After around an hour, the crosscompiler was ready:

du -shc ../x-tools/

364M../x-tools/
364Mtotal

Build the Kernel

Now that we have a crosscompiler, we can get back to the kernel directory, configure the tool paths, and compile a new kernel:

cd /data/matelakat/kernel/linux-3.10.32/
cp /data/matelakat/vmfromscratch/linux/.config ./
make oldconfig
make menuconfig
make -j 4

Unfortunately, I didn't measure the time it took, but it was quite fast

Build the Root Filesystem

Now that I have a nice kernel I also need a root filesystem. Buildroot will help me to build that:

mkdir /data/matelakat/br
cd /data/matelakat/br
wget -qO - http://buildroot.uclibc.org/downloads/buildroot-2014.02.tar.gz | tar -xzf -
cd buildroot-2014.02/
cp /data/matelakat/vmfromscratch/buildroot/config .config
make menuconfig
make

Putting it all together

Now that I have everything, I only need to create an iso cd with my new system

mkdir isoroot
cp ../br/buildroot-2014.02/output/images/rootfs.cpio.gz isoroot/initrd.img
cp ../kernel/linux-3.10.32/arch/i386/boot/bzImage isoroot/
cp ../br/buildroot-2014.02/output/images/isolinux.bin isoroot/isolinux/
cp isolinux.cfg isoroot/isolinux/
mkisofs -J -o minsys.iso -b isolinux/isolinux.bin -c isolinux/boot.cat -no-emul-boot -boot-load-size 4 -boot-info-table isoroot/
qemu-system-i386 -M pc -cdrom minsys.iso -net nic,model=e1000 -net user

Next steps

My next step will be to automate all these things.

PDF - Two pages per page to one pages per page

So we had a PDF, it's size was 297 x 215 mm. Each page of this PDF contained two pages, like this:

 Page 1 of the input file                       Page 1 of output   Page 2 of output
    +------------------------------+            +---------------+  +---------------+
    |               |              |            |               |  |               |
    |               |              |            |               |  |               |
    |               |              |            |               |  |               |
    |               |              |            |               |  |               |
    |               |              |            |               |  |               |
    | Page 1        | Page 2       |            |   Page 1      |  |   Page 2      |
    |  of the book  |  of the book |            |    of the book|  |    of the book|
    |               |              |            |               |  |               |
    |               |              |            |               |  |               |
    |               |              |            |               |  |               |
    |               |              |            |               |  |               |
    |               |              |            |               |  |               |
    +------------------------------+            +---------------+  +---------------+
                                     +------->
 Page 2 of the input file            +------->  Page 3 of output   Page 4 of output
    +------------------------------+            +---------------+  +---------------+
    |               |              |            |               |  |               |
    |               |              |            |               |  |               |
    |               |              |            |               |  |               |
    |               |              |            |               |  |               |
    |               |              |            |               |  |               |
    | Page 3        | Page 4       |            |   Page 3      |  |   Page 4      |
    |  of the book  |  of the book |            |    of the book|  |    of the book|
    |               |              |            |               |  |               |
    |               |              |            |               |  |               |
    |               |              |            |               |  |               |
    |               |              |            |               |  |               |
    |               |              |            |               |  |               |
    +------------------------------+            +---------------+  +---------------+

So to do this, I extracted the left sides as page-0.pdf, and the right sides as page-1.pdf to the folder out, and the n joined these together:

#!/bin/bash
set -eux

# Default resolution is 720 dpi
# For points, use 72 dpi

# The actual pdf was 297 x 215 mm --(720 dpi)----> 8418 x 6094 pixels
# I only want to extract half of it -------------> 4209 x 6094
# For the right page, I need an offset -(72 dpi)-> -421.0 0

INPUT_FILE="$1"

rm -rf ./out
mkdir out

ghostscript -o "out/%d-0.pdf" -sDEVICE=pdfwrite -g4209x6094 \
-c "<</PageOffset [0 0]>> setpagedevice" -f "$INPUT_FILE"

ghostscript -o "out/%d-1.pdf" -sDEVICE=pdfwrite -g4209x6094 \
-c "<</PageOffset [-421.0 0]>> setpagedevice" -f "$INPUT_FILE"

ghostscript -o "singlepage-$INPUT_FILE" -sDEVICE=pdfwrite -dPDFSETTINGS=/ebook \
    $(ls out/* | sort -V)

rm -rf ./out

References:
http://superuser.com/questions/54054/convert-pdf-2-sides-per-page-to-1-side-per-page

Back to school - Coursera - Crypto, Control Theory, Android

After KR told me that he signed up for a Cryptography course on Coursera, I decided to do the same. I learned crypto at Uni, but that was a long time ago, so I thought, it's time to refresh my memories. The story does not end here, as this weekend, I signed up to two more courses: an Android course, and a Robot Control course. I'm a bit behind at the moment for each of the courses. I find this Coursera amazing, and I hope my wife won't kill me before I finish these courses. Should you be interested, here is a list of the courses that I started:

• https://class.coursera.org/crypto-009
• https://class.coursera.org/conrob-002
• https://class.coursera.org/android-001

I just started to watch the video lectures for the Android class, and watching this video atm as recommended by the professor: