Category Archives: EC2

Using Paramiko to control an EC2 instance

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An example of using Paramiko to issue commands to an EC2 instance

Summary

An example of using the Python library Paramiko to ‘remote control’ an EC2 instance .

“Do that, Do this”

Recently I’ve been looking into the use of the Bellatrix library to start, control and stop Amazon EC2 instances (my posts about that are here and here).

Spinning off the side of that I’ve taken a look at the Paramiko module which “implements the SSH2 protocol for secure (encrypted and authenticated) connections to remote machines”.

There’s a good article on beginning to use Paramiko “SSH Programming with Paramiko” by Jesse Noller which I found very helpful but there’s enough stuff I had to change to deal with using EC2 and the controlling Python script running on Windows that I thought it would be worth recording my sample script.

Installing Paramiko

So first off I’d seen the comments about Paramiko maybe needing a special compilation step for installation to Windows but I’m pleased to say that’s not true, I downloaded 1.7.7.1 to my Windows Vista machine, did a quick…

python setup.py install

… and it all went very smoothly, just to be sure I tried out an import …

>>> import paramiko

… no problem.

Starting the EC2 instance

I now needed a server to talk to so I used Bellatrix to spin up a micro instance of Ubuntu like this :

python "C:\bin\installed\Python2.6\Scripts\bellatrix" start --security_groups mySecGrp ami-3e9b4957 mykeypair

The arguments you can see here are :

  • “mySecGrp” is a Security Group I’ve previously setup via the AWS Management Console;
  • ‘ami-3e9b4957’ is the AMI of Ubuntu 10.04 (Lucid Lynx); and
  •  ‘mykeypair’ is the name of a Key Pair that, again, I’ve previously setup via the AWS Management Console.

When you run that command you get an output that looks like this :

C:\Users\Richard Shea>python "C:\bin\installed\Python2.6\Scripts\bellatrix" start --security_groups mySecGrp ami-3e9b4957 mykeypair
2012-04-19 21:27:03,135 INFO starting EC2 instance...
2012-04-19 21:27:03,180 INFO ami:ami-3e9b4957 type:t1.micro key_name:mykeypair security_groups:mySecGrp new size:None
2012-04-19 21:27:07,657 INFO starting image: ami-3e9b4957 key mykeypair type t1.micro shutdown_behavior terminate new size None
2012-04-19 21:27:08,555 INFO we got 1 instance (should be only one).
2012-04-19 21:27:08,556 INFO tagging instance:i-f1234567 key:Name value:Bellatrix started me
2012-04-19 21:27:12,361 INFO instance:i-f1234567 was successfully tagged with: key:Name value:Bellatrix started me
2012-04-19 21:27:12,361 INFO getting the dns name for instance: i-f1234567 time out is: 300 seconds...
2012-04-19 21:27:34,173 INFO DNS name for i-f1234567 is ec2-10-20-30-40.compute-1.amazonaws.com
2012-04-19 21:27:34,173 INFO waiting until instance: i-f1234567 is ready. Time out is: 300 seconds...
2012-04-19 21:27:34,174 INFO Instance i-f1234567 is running

And the key thing here is that we now now have access to the host name of the EC2 instance we’ve just spun up:

ec2-10-20-30-40.compute-1.amazonaws.com

Talking to the EC2 instance

We’re now ready to send commands to our new instance. Making use of some of Jesses code I was able to write :

import paramiko
ssh = paramiko.SSHClient()
ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
ssh.connect('ec2-107-22-80-32.compute-1.amazonaws.com',
            username='ubuntu',
            key_filename='''mykeypair-ssh2-rsa.openssh''')
stdin, stdout, stderr = ssh.exec_command("uptime;ls -l;touch mickymouse;ls -l;uptime")
stdin.flush()
data = stdout.read().splitlines()
for line in data:
    print line
ssh.close()

Anyone who’s got this far can probably see what’s happening here, but just to be sure :

  1. having instantiated an instance of paramiko.SSHClient we’re able to use our private key file and the address of our EC2 server to start an SSH session.
  2. We then use the exec_command method to submit a string of commands and get back three references to files corresponding to : standard input, standard output and standard error.
  3. By reading through the standard output file we can print locally the output from the commands executed on the EC2 instance.

The Key Thing

As you can see to identify ourselves to the remote server we’re doing a key exchange. Our private key is ‘mykeypair-ssh2-rsa.openssh’. A point worth mentioning here is that generally I logon to EC2 instances using the excellent PuTTY . The private key files used by default by PuTTY are not in the same format as the ones required by Paramiko so as a result when I first tried this I found Paramiko fell over complaining my ‘key_filename’ argument was ‘not a valid dsa private key file’.

PuttyGen to the rescue

Well the great thing is that PuTTY actually comes with a tool PuttyGen which will import a standard PuTTY key file (foo.ppk) – you need to do ‘Conversions’ | ‘Import Key’ and then ‘Conversions’ | ‘Export OpenSSH Key’

Ubuntu Specific

Bear in mind that the way the SSHClient connect method is used above is suitable for an Ubuntu instance as it is by default however you can’t rely on all *nix instance working just that way.

Seeing the Output

Just to close out I’ll show you the output

12:39:45 up  3:12,  0 users,  load average: 0.08, 0.02, 0.01
total 0
total 0
-rw-r--r-- 1 ubuntu ubuntu 0 2012-04-19 12:39 mickymouse
12:39:45 up  3:12,  0 users,  load average: 0.08, 0.02, 0.01

Powerful Stuff

The combination of Bellatrix allowing you to spin up EC2 instances with a single command and Paramiko allowing you send arbitary commands to those servers is powerful stuff and I’m impressed at the work done by their respective developers. Of course Bellatrix can do ‘for free’ what I’ve used Paramiko to do here are part of it’s Provisioning commands but it was an interesting exercise for me to do my own version of that.

Bellatrix Provisioning Commands

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A quick guide to built-in Bellatrix provisioning commands

Summary

A table of Bellatrix provisioning commands as at 1.1.2

Bellatrix Provisioning

As mentioned in my previous post Bellatrix allows you to start and provision Amazon Web Services EC2 instances.In this context ‘provision’ refers to the process of installing software, creating directories, changing file permissions etc.

The built in commands are documented here in the official doco but before I found that I’d ripped the cmds.py file apart and produced the following table. It’s a little more succinct than the official version so I think it’s worth publishing here.

Version Alert

For obvious reasons this type of thing is prone to Bellatrix changing. This page is valid as of the 1.1.2 version of Bellatrix.

Provisioning Commands

Command Description
apt_get_install Return the “sudo apt-get install” command
apt_get_update Executes apt-get update.
chmod Applies the chmod command
createSoftLink Creates a new soft link
copy Copy a file using -f so it doesn’t fail if the destination exists
create_django_project Creates a Django project
createVirtualEnv Generate a new Python virtual environment using virtualenv
executeInVirtualEnv Execute a command within a virtualenv environmen
flatCommands Given a list of commands it will return a single one concatenated by ‘&&’ so they will be executed in sequence until any of them fail
install_pip Install pip using apt-get install
install_nginx Install Nginx in Ubuntu using the repo they provide as described in http://wiki.nginx.org/Install#Ubuntu_PPA
installPackageInVirtualEnv Install a Python package into a virtualenv
mkdir Created a new directory. “-p” flag is used so the command generates the same result regardless whether the directory exists or not.
pip_install Install a Python package using pip
sudo Execute a list of commands using sudo
wget Downloads a web resource using wget

Bellatrix + Windows Users – Two things to remember

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Bellatrix – Windows Idiosyncracies

Summary

Two things you might find useful if you’re starting to use Bellatrix on Windows.

What’s Bellatrix Again ?

Bellatrix allows you browse and control Amazon EC2 instances using simple commands on your local machine.

For instance :

bellatrix start ami key_name

run on your machine will launch an EC2 instance within Amazon Web Services based on the named ami (Amazon Machine Image) and allow you to contact it using the key_name you have specified.

You’ve been able to do something like this with the Python package Boto for some time but Bellatrix provides a lot of ready to use commands rather than having to write your own scripts.

Bellatrix on Windows Then ?

Location of Home

I’m a bit embarrassed to write this but in the Bellatrix doco which describes what config files you need and where to place them it refers to

<your_home>

I’m familiar with the idea of ‘Home’ on a unix box but in a Windows enviroment ? I wasn’t really sure what it meant (I’ve only been using Windows for 15 years so you can see where the confusion crept in). I managed to persuade myself it was referring to the Bellatrix directory within the Python site-packages directory !

Well here’s the news for the Windows users out there who are as ‘home-challenged’ as I am. It turns out you should putting those config files in a directory located at :

%HOMEPATH%\.bellatrix

which for me is

C:\Users\Richard Shea\.bellatrix

Yes but what about the dots ?

Which brings me onto another windows specific thing – how do you produce a directory with a dot as its first character ? I started off trying to do it via File Explorer and discovered something strange. File Explorer won’t let you specify a directory name that starts with a dot … unless you specify the directory name as having a trailing dot as well … if you do that File Explorer quietly throws away the trailing dot and you have the name you wanted in the first place ! Weird … or perhaps “only on Windows”

In closing

Anyway the good news is I’ve got it up and running and listing my instances ! Next step is to to use Bellatrix to start an EC2 instance and provision it as a Nagare environment. There’ll be a blog post about that by the time I’ve done, I’m sure !