Getting a larger root volume on a cluster compute instance

At this point, all of the Ubuntu EBS root images are 8GB. This is nice and small. I previously covered how you could increase the size of those disks.

On Cluster Compute instances, its a bit more difficult. The cluster compute instances have their root filesystem in a partition inside of the disk attached. Thats all well and good, and most likely a partitioned disk is more familiar to you than one that is not partitioned. The cluster compute images have grub2 installed in the MBR of that disk.

The problem with the partition on the disk is that you can no longer simply launch the instance with a larger root volume and then 'resize2fs /dev/sda1'. This is because the kernel won't re-read the partition table of a disk until all of its partitions are unmounted. For the disk that holds your root partition, that means you basically have to reboot after a change.

To avoid that waste of precious time, we've included a utility called 'growpart' inside of the initramfs on the Ubuntu images. It is invoked by the 'cloud-initramfs-growroot' package. This code runs before the root fileystem is busy, so the request for the kernel to re-read the partition table will work without requiring a reboot. To try it out, do:


# us-east-1 ami-1cad5275 hvm/ubuntu-natty-11.04-amd64-server-20110426
$ ec2-run-instances --region us-east-1 --instance-type cc1.4xlarge \
--block-device-mapping /dev/sda1=:20 ami-1cad5275


When you get to the instance, you'll have a 20G filesystem on /. And, if you're interested enough to look in the console output, you'll see something like:

GROWROOT: CHANGED: partition=1 start=16065 old: size=16755795 end=16771860 new: size=41913585,end=41929650


start a 11.04 instance with a larger root filesystem

In order to fit inside the Amazon "Free Tier", Ubuntu made the decision to change its root volume size from 15G to 8G. That decision was made for all refreshed EBS root images. So, our current set of 10.04, 10.10 and 11.04 images have 8G root filesystems.

If you find that space somewhat limiting, it is easy to give yourself a larger root volume at instance creation time. Its easy

Launch the instance with appropriate block-device-mapping arguments


$ ec2-run-instances $AMI --key mykey --block-device-mapping /dev/sda1=:20


That will create you an instance with a 20G root volume. However the filesystem on that volume will still only occupy 8G of the space. Essentially, you'd have 12G of unused volume at the end of the disk.

Resize the root volume

if you've launched an 11.04 based image newer than alpha-2, this step is not necessary. Cloud-init will do it for you. It is just assumed that you want your root filesystem to fill all space on its partition. I honestly cannot think of a reason why you would not want that.

Now, if you are using 10.04 or 10.10 images, you can resize your root volume easily enough after the boot. Just login, and issue:


$ sudo resize2fs /dev/sda1

That operation should take only a few seconds or less, and you'll then have all the space you need.

Migrating to pv-grub kernels for kernel upgrades

After the release of the Ubuntu 10.04 LTS images that use the pv-grub kernel, there were some questions on what to do if you're running from an older AMI and want to take advantage of what pv-grub offers.

Heres a short list of how you might be affected:

• If you are running an EBS root instance launched from or rebundled from an Official Ubuntu image of 10.04 LTS (Lucid Lynx) released 20110201.1 or later, 10.10 (Maverick Meerkat), Natty Narwhal, or later, then you do not need to do anything. You already are using pv-grub, and can simply apply software updates and reboot to get new kernel updates. You can stop reading now.
• If you are running an instance-store instance that is not using a pv-grub kernel, there is nothing you can do. There is simply no way to change the kernel of an instance store instance.
• If you are running an EBS-root based instance rebundled from a Ubuntu 9.10 (Karmic Koala) or older, then there is currently no supported path to getting kernel upgrades. There were no officially released EBS-root based Ubuntu images of 9.10, and with Karmic's end of life coming in April, there is not likely to be support for this new feature.
• If you are running an EBS-root instance launched from or rebundled from an official Ubuntu release of 10.04, read on.

Updating a 10.04 based image basically entails 2 steps, setting up /boot/grub/menu.lst, and then modifying your instance to have a pv-grub kernel.

Step 1: installing grub-legacy-ec2.

If you launched or rebundled your instance from an Ubuntu 10.04 numbered 20101020 or earlier, you need to do this step. If you started from a release of 20101228 you can skip this step.

• Apply software updates.
  
  Depending on how out of date you are, this might take a while.
  
  
sudo apt-get update && sudo apt-get dist-upgrade

  
• Install grub-legacy-ec2
  
  

  The 'grub-legacy-ec2' package is what the images use to manage /boot/grub/menu.lst. If you had used Ubuntu prior to the default selection of grub2, you will be familiar with how it works. grub-legacy-ec2 is basically just the menu.lst managing portion of the Ubuntu grub 0.97 package with some EC2 specifics thrown in.

  To get a functional /boot/grub/menu.lst, all you have to do is:

  
sudo apt-get install grub-legacy-ec2

  

Step 2: modifying the instance to use pv-grub kernels

Now, your images should have a functional /boot/grub/menu.lst, and grub-legacy-ec2 should be properly installed such that future kernels will get automatically added and selected on reboot. However, you have to change your instance to boot using pv-grub rather than the old kernel aki that you originally started with.

• Shut down the instance
  
  The best way to do this is probably to just issue '/sbin/poweroff' inside the instance. Alternatively, you could use the ec2 api tools, or do so from the AWS console.
  
% sudo /sbin/poweroff

  
• Modify the instance's kernel to be a pv-grub kernel
  
  Once the instance is moved to "stopped" state, you can modify its kernel to be a pv-grub kernel. The kernel you select depends on the arch and region. See the table below for selecting which you should use:
  

  region	arch	aki id
  ap-southeast-1	x86_64	aki-11d5aa43
  ap-southeast-1	i386	aki-13d5aa41
  eu-west-1	x86_64	aki-4feec43b
  eu-west-1	i386	aki-4deec439
  us-east-1	x86_64	aki-427d952b
  us-east-1	i386	aki-407d9529
  us-west-1	x86_64	aki-9ba0f1de
  us-west-1	i386	aki-99a0f1dc

  
  Then, assuming you have $AKI represents the appropriate aki above, and $IID represents your instance id, and $REGION represents your region, you can update the instance and then start it with:
  
$ ec2-modify-instance-attribute --region ${REGION} --kernel ${AKI} ${IID}
$ ec2-start-instances --region ${REGION} ${IID}

  

Your instance will start with a new hostname/IP address, so get that out of describe-instances and ssh to your instance. You can check that it has worked by looking at /proc/cmdline. Your kernel command line should look something like this:


$ cat /proc/cmdline
root=UUID=7233f657-c156-48fe-8d60-31ae6400d0cf ro console=hvc0


In the future, your instance will now behave much more like a "normal server". If you apply software updates (apt-get dist-upgrade) and reboot, you'll boot into a fresh new kernel.

Getting ephemeral devices on EBS images

When you launch an instance in EC2, be it EBS root or instance-store, you are "entitled" to some amount of ephemeral storage. Ephemeral storage is basically just extra local disk that lives in the host machine where your instance will run. How much instance-store disk you are entitled to is described with the instance size descriptions.

The described amount of ephemeral storage is allocated to all instance-store instances. However, at register time of EBS-root instances the default "block-device-mapping" is set. Because an EBS-root AMI may be run with different instance-types, it is impossible to set the correct mapping for all scenarios. For the Ubuntu images, the default mapping only includes ephemeral0, which is present in all but t1.micro sizes.

So, if you want to "get all that you're paying for", you'll have to launch instances with different '--block-device-mapping' arguments to ec2-run-instances (or euca-run-instances). I've written a little utility named bdmapping to make that easier, and hold the knowledge.

You can use it to show the mappings for a given instance type:


$ ./bdmapping
--block-device-mapping=sdb=ephemeral0 --block-device-mapping=sdc=ephemeral1


Or, use it with command substitution when you launch an instance:

$ ec2-run-instances $(bdmapping -c m1.xlarge) --key mykey ami-c692ec94
#
# the above is the same as running:
# ec2-run-instances --block-device-mapping=sdb=ephemeral0 \
# --block-device-mapping=sdc=ephemeral1 --instance-type=m1.large \
# --key mykey ami-c692ec94


You can view or download 'bdmapping' at https://gist.github.com/809587

New Ubuntu 10.04 LTS images with pv-grub support

Yesterday I announced the availability of updated Ubuntu images on EC2 for 10.04 LTS (Lucid Lynx).

This post is mainly to mirror that one to a possibly wider audience, but also to go into more detail on the key change in these images:

You can now upgrade the kernel inside your 10.04 based EC2 image by running 'apt-get update && apt-get dist-upgrade && reboot!

Now, for a little more detail on that.

Around the time that 10.04 released, or shortly there after, Amazon released a new feature of EC2 as "Use Your Own Kernel with Amazon EC2". What this really meant was that there were now "kernels" on EC2 that were really versions of grub. By selecting this kernel, and providing a /boot/grub/menu.lst inside your image, the instance would be in control of the kernel booted. Previously, the loading of a kernel was done by the xen hypervisor, and could not be changed at all for a instance-store image, and only non-trivially for an EBS-root instance

Yes, you read that right, midway through the year of 2010 you were able to change the kernel that you were running in an EC2 instance with a software update and a reboot.

We took advantage of this support in our 10.10 images, but for many people, only LTS (Long Term Support) releases are interesting. So, to satisfy those people, we've brought the function into our 10.04 images.

If you're using our images, or have rebundled an image starting from them, I *strongly* suggest updating to the 20110201.1 images or anything later. You'll want to do that because

• You can receive kernel upgrades as normal software upgrades to your running instance.
• This is by far the most supportable route for upgrade from 10.04 to our next LTS (12.04). If your instance is not using the pv-grub kernel, and you want to upgrade to a newer release, you will have to upgrade, shutdown the instance, modify the associated kernel, and start up the instance. That is both more painful, and will result in larger downtime.
  

So, in short, grab our new images!

Failsafe and manual management of kernels on EC2

On 10.10 and later, Ubuntu images use the Amazon provided pv-grub to load kernels that live inside the image. The selected kernel is controlled by /boot/grub/menu.lst. This makes it possible to install a new kernel via 'dpkg -i' or 'apt-get dist-upgrade' and then reboot into the new kernel.

The file /boot/grub/menu.lst is managed by grub-legacy-ec2 package. The program 'update-grub-legacy-ec2' is called on installation of Ubuntu kernels through files that are installed in /etc/kernel/postinst.d and /etc/kernel/postrm.d.

By default, as with other Ubuntu systems, the kernel with the highest revision will be the behavior will be automatically selected as the default, and selected on the next boot. Because EC2 images is read-only, you may want to manually manage your selected kernel. This can be done by modifying /boot/grub/menu.lst to use the grub "fallback" code.

I'll launch an instance of the current released maverick (ami-ccf405a5 in us-east-1 ubuntu-maverick-10.10-i386-server-20101225). Then, on the instance, create hard links to the default kernel and ramdisk so even on apt removal, they'll stick around, and then change /boot/grub/menu.lst to use those kernels.


sudo ln /boot/vmlinuz-$(uname -r) /boot/vmlinuz-failsafe
sudo ln /boot/initrd.img-$(uname -r) /boot/initrd.img-failsafe


Then, copy the existing entry in /boot/grub/menu.lst to a new entry above the automatic section. I've changed/added:


# You can specify 'saved' instead of a number. In this case, the default entry
# is the entry saved with the command 'savedefault'.
# WARNING: If you are using dmraid do not use 'savedefault' or your
# array will desync and will not let you boot your system.
default saved

...<snip>...

# Put static boot stanzas before and/or after AUTOMAGIC KERNEL LIST

# this is the failsafe kernel, it will be '0' as it is the first
# entry in this file
title Failsafe kernel
root (hd0)
kernel /boot/vmlinuz-failsafe root=LABEL=uec-rootfs ro console=hvc0 FAILSAFE
initrd /boot/initrd.img-failsafe
savedefault

title Ubuntu 10.10, kernel 2.6.35-24-virtual
root (hd0)
kernel /boot/vmlinuz-2.6.35-24-virtual root=LABEL=uec-rootfs ro console=hvc0 TEST-KERNEL
initrd /boot/initrd.img-2.6.35-24-virtual
savedefault 0


And then update grub to store that the first kernel is the 'saved', which for grub 1 (or 0.97) modifies /boot/grub/default.


sudo grub-set-default 0
sudo reboot


Now, a reboot will boot into the failsafe kernel (which we can verify by checking /proc/cmdline) and see 'FAILSAFE'. Then, to test our "TEST-KERNEL", run:


sudo grub-set-default 1
sudo reboot


After this reboot, the system come up into "TEST-KERNEL" (per /proc/cmdline) but /boot/grub/default will contain '0', indicating that on subsequent boot, the FAILSAFE will run. In this way, if your kernel failed to boot all the way up, you can then just issue:


euca-reboot-instances i-15b77779


And you'll boot back into the FAILSAFE kernel.

The above basically allows you to manually manage your kernels while letting grub-legacy-ec2 still write entries to /boot/grub/menu.lst.

I chose to use hardlinks for the 'failsafe' kernels, so that even on dpkg removal, the files would still exist. Because the 10.10 Ubuntu kernels have the EC2 network and disk drivers built in, you'll still be able to boot even after a dpkg removal of the failsafe kernel or an errant 'rm -Rf /lib/modules/2*'

Using euca2ools rather than ec2-api-tools with EC2

The Ubuntu UEC Images that Ubuntu produces on EC2 are in every way fully supported, "Official Ubuntu". As with other official releases, access to source code for security and maintenance reasons affects our decisions on what is included.

In the UEC images, the most notable packages left out are 'ec2-api-tools' and 'ec2-ami-tools'. I personally use the ec2-api-tools and ec2-ami-tools quite frequently and Amazon has done a great job with them. However, the license and lack of source code prevents them from being in Ubuntu 'main'.

Fortunately
a.) There are packages made available in the Ubuntu 'multiverse' component.
b.) The euca2ools package is installed by default and provides an almost drop in replacement for the ec2-api-tools and ec2-ami-tools.

I think that many users of EC2 aren't aware of the euca2ools, so I'd like to give some information on how to use them here.

The ec2-api-tools use the SOAP interface and thus use the "EC2_CERT" and "EC2_PRIVATE_KEY". The euca2ools sit on top of the excellent boto project. Boto uses the AWS REST api, which means authentication is done with your "Access Key" and "Secret Key". As a result, configuration is a little different. (Note, bundling images, you still need the EC2_CERT and EC2_PRIVATE_KEY for encryption/signing).

Configuration for euca2ools can be done via environment variables (EC2_URL, EC2_ACCESS_KEY, EC2_SECRET_KEY, EC2_CERT, EC2_PRIVATE_KEY, S3_URL, EUCALYPTUS_CERT) or via config file. I personally prefer the configuration file approach.

Here is my ~/.eucarc that is configured to operate with the EC2 us-east-1 region.

CRED_D=${HOME}/creds/aws-smoser
EC2_REGION="${EC2_REGION:-us-east-1}"
EC2_CERT=${CRED_D}/cert.pem
EC2_PRIVATE_KEY=${CRED_D}/pk.pem
EC2_ACCESS_KEY=ABCDEFGHIJKLMNOPQRST
EC2_SECRET_KEY=UVWXYZ0123456789abcdefghijklmnopqrstuvwx
EC2_USER_ID=950047163771
EUCALYPTUS_CERT=/etc/ec2/amitools/cert-ec2.pem
EC2_URL=https://ec2.${EC2_REGION}.amazonaws.com
S3_URL=https://s3.amazonaws.com:443


Things to note above:

• euca2ools sources the ~/.eucarc file with bash, and then reads out the values of EC2_REGION, EC2_CERT, EC2_PRIVATE_KEY, EC2_ACCESS_KEY, EC2_USER_ID, EC2_URL, S3_URL. This means that you use other bash functionality in the config file as I've done above with 'EC2_REGION'. This allows me to do something like:
  
EC2_REGION=us-west-1 euca-describe-images

  
• If there is no configuration file specified with '--config', then those values will be read from environment variables


• Amazon's public certificate from the ami tools is included with euca2ools in ubuntu, and located in /etc/ec2/amitools/cert-ec2.pem


• Many of the euca2ools commands will run significantly faster than the ec2-api-tools. The reason for slowness of the ec2-api-tools is their man java dependencies (please correct me if I'm wrong).
  
• Your ~/.eucarc file contains credentials and therefore it should be protected with filesystem permissions (ie 'chmod go-r ~/.eucarc').
  

Hopefully this will make it easier for you to use euca2ools with EC2 on Ubuntu.