Compute Resources

“Infrastructure as a Service” cloud infrastructures provide computing resources through “virtual machines”. For end users, these virtual machines act just like physical machines, except that they can be provisioned quickly with exactly the configuration desired.

This section starts with a description of the Marketplace, a catalog of virtual machine images, and then covers how to start, access, and stop virtual machine instances.

Appliance Marketplace

All virtual machine instances are created from virtual machine images (or appliances) that contain the starting configuration for the virtual machine.

For StratusLab clouds, the Marketplace contains a database of all of the available appliances. These include standard appliances created and maintained by the StratusLab developers as well as appliances created by other StratusLab users.

Use your web browser to view the available appliances by navigating to the central Marketplace. You can find the standard images from StratusLab by putting “” into the “endorser” field on the right side of the interface.

The summary contains the basic information for an appliance along with a link to find more information. The most imporant bit of information is the image identifier. This is a 27 character Base 64 value that uniquely identifies the appliance. This identifier is used to select the appliance you want to run as a virtual machine.

StratusLab provides minimal distributions of CentOS 6, ScientificLinux 6, Ubuntu 12.04, and Ubuntu 14.04. These follow the best practices for appliance creation and are kept up to date with security patches. They make good starting points for creating your own appliances.


Use your web browser to navigate through the Marketplace. Use the search widget on the right to see what appliances are available. Use the search widget to find all of the appliances created by the StratusLab collaboration.

Virtual Machine Lifecycle

The virtual machine lifecycle consists of the following commands:

$ stratus-run-instance ${APP_ID}  # APP_ID from the Marketplace
                                  # returns VM_ID and VM_IP
$ stratus-describe-instance ${VM_ID}

# Connect to the deployed virtual machine
$ stratus-connect-instance ${VM_ID}
$ ssh root@${VM_IP}

$ stratus-kill-instance ${VM_ID}

These commands start, list, access, and destroy a virtual machine, respectively.

The stratus-run-instance command starts a new virtual machine instance. It requires the appliance or image identifier from the Marketplace (APP_ID). This will return the virtual machine identifier (VM_ID) and its assigned IP address (VM_IP).

The stratus-describe-instance command displays the information about virtual machines. Without an argument, it will provide a concise summary for all non-terminated virtual machines. If you provide a virtual machine identifier, then only information for that machine will be returned. More detailed information can be obtained by using the --verbose option.

You can log into your virtual machine using SSH. Your public SSH key will have been transferred to the machine and will allow you to log into the machine as root. Use stratus-connect-instance ${VM_ID} or just ssh root@${VM_IP} to log into the machine. Depending on the operating system, resources, etc., it can take several minutes to have access to a virtual machine.


The stratus-connect-instance command does not work on Windows. Use your local SSH command or application to connect to your virtual machine.

The stratus-kill-instance command stops a virtual machine and releases all of the allocated resources. Virtual machines that have been terminated will no longer appear in the stratus-describe-instance output by default.


The stratus-kill-instance stops a running virtual machine instantly. This is the equivalent of pulling out the plug. A more graceful shutdown should be done in most cases: halt the virtual machine (with halt or shutdown within the machine) and then run stratus-kill-instance.


Choose one of the standard appliances (e.g. Ubuntu 14.04) and use these commands to go through the lifecycle for a virtual machine. How long was it before you could ping the virtual machine? How long before you could log in?

Allocated Resources

The resources allocated to virtual machines can be defined with options at deployment time. StratusLab does not allow the resource allocations for existing virtual machines to be changed.

A set of predefined “machine types” provide some default configurations.

You can see the predefined configurations with the command:

$ stratus-run-instance --list-types
 Type             CPU       RAM      SWAP
  c1.medium       2 CPU    1536 MB    1536 MB
  c1.xlarge       4 CPU    6144 MB    6144 MB
  m1.large        2 CPU    6144 MB    6144 MB
  m1.medium       1 CPU    3072 MB    3072 MB
* m1.small        1 CPU    1536 MB    1536 MB
  m1.xlarge       4 CPU    8192 MB    8192 MB
  t1.micro        1 CPU     512 MB     512 MB

The values for the CPU, RAM (MiB), and SWAP (MiB) space are listed for each type with the default type marked with an asterisk. You can change which type is selected by using the --type option when starting a virtual machine.

Fine-grained control over the resource allocation is also possible. The options --cpu, --ram, and --swap allow you to set these values separately. For values that are not specified explicitly, the value will be taken from the selected machine type.


When logged into a virtual machine, can you determine how many CPUs were allocated and how much memory? You can find this information by looking at /proc/meminfo and /proc/cpuinfo, for example.


Use the --type, --cpu, and --ram options to change the allocated resources for a virtual machine. Verify that the correct amount of resources has been allocated.


Contextualization is the process by which a virtual machine discovers characteristics of its environment and properly configures itself. This is used, for example, for network configuration but can also be used for user-level service configuration.

Unfortunately, there is no standard for the contextualization process, although the CloudInit process is slowly becoming a de facto standard.

StratusLab supports two contextualization mechanisms: HEPiX/OpenNebula and CloudInit. For historical reasons the HEPiX/OpenNebula mechanism is currently the default.

HEPiX Contextualization

The HEPiX/OpenNebula contextualization passes information from the user (given with the stratus-run-instance command) to the virtual machine via a CD-ROM image. The virtual machine automatically mounts the CD-ROM image and executes a contextualization script using the information from the image.

You public SSH key is automatically passed to the virtual machine using this mechanism. Additional key-value pairs can be passed to the virtual machine via the --context parameter.

The context information can be seen on the client side by using the stratus-describe-instance -vvv ${VM_ID} command. This displays all of the information defining a given virtual machine.

From within the virtual machine, you can mount the CD-ROM image (if it isn’t already mounted) to see what scripts and what information has been passed from the client to the virtual machine. You can find the image by using the blkid command. CD-ROMs have the type “iso9660”.


Start a virtual machine. Log into the virtual machine, find the context CD-ROM, and mount it. What files are there? How are these executed in the startup process? (Hint: Look in /etc/init.d/.)


Use the context options to start another virtual machine. How are the key-value pairs you defined passed into the virtual machine? Can you imagine how to use this information to configure a service on the machine?

CloudInit Contextualization

CloudInit is a very flexible contextualization mechanism that is becoming a de facto standard. StratusLab supports this mechanism. You can make CloudInit the default contextualization mechanism by setting the default_context_method value in your configuration file:

default_context_method = cloud-init

You can set this for a specific cloud infrastructure or globally in the defaults section.

To start a virtual machine using CloudInit, use the --cloud-init option or the --context-method option. The following two commands have the same effect:

$ stratus-run-instance --cloud-init "" \

$ stratus-run-instance --context-method cloud-init \

The --cloud-init option requires a value. Passing the empty string will use the default, which is to pass your SSH public key as for the HEPiX/OpenNebula contextualization.

Ubuntu provides good documentation for CloudInit describing what can be passed to the virtual machine.

To demonstrate the flexibility, we will show how to use CloudInit to start up a web server on a CentOS virtual machine. Create a file called with the contents:

#!/bin/bash -x

yum install -y httpd

cat > /var/www/html/test.txt <<EOF

chkconfig httpd on

service httpd start

This will install, configure, and run the web server on the virtual machine.

Pass this script to a virtual machine based on a CentOS image:

$ stratus-run-instance \
    --cloud-init "x-shellscript," \

After a couple of minutes, you should be able to visit the url to see a page containing “SUCCESSFUL TEST”.

If you want to pass multiple files, you can separate the mimetype/file pairs with hash (#) characters or use the stratus-prepare-context and then the --context-file option of stratus-run-instance.


Start a virtual machine with CloudInit. Log into the virtual machine, find the context VFAT disk, and mount it. What files are there? How are these executed in the startup process?


Do the same exercise for an Ubuntu machine? What did you have to change to get this to work? Can you install and configure another service on a virtual machine that would be visible from your web browser?