Creating an Instance


Instances are virtual machines that run inside the cloud. More simply, an instance is just a digital version of a physical computer. Instances are the basic “unit” of compute you will use within CUmulus. Once you have requested a CUmulus allocation, you will be provided with a “project” which contains the total resources you requested. Within your project, you can spin up a finite number of instances (determined by your allocation), each of which can be thought of as a computer.

Create New Instance

Follow the docs below for general instance creation or follow our step-by-step tutorial.

Launch Instance

Click on Launch Instance button on the top bar from the “Instances” page (step 4 above). This will bring up the instance launcher which will guide you in creating your new instance by selecting your operating system, allocating resources, choosing security groups, and adding security keys. We’ll go through each step one at a time:

Step 1: Details

  • Fill out the instance name and description

    Availability zone and count can be left as default. This value is set to the availability zone given by the cloud provider (for example, us-west or apac-south).


Note: if launching Windows Server, the hostname will be truncated if greater than 15 characters in the OS
  • click Next when done to go to the Source screen.

Step 2: Source

Select boot source.

  • Choose an operating system from the list of images CURC provides.
  • Choose a storage volume size
    • Choosing an image will auto-populate the size, warning you if it is too small
  • Choose to have your storage volume deleted on Instance Deletion
    • If you select No be aware “zombie” volumes will remain when the instance is deleted (you will need to remove them manually later!)


  • click Next when done to go to the Flavor screen.

Step 3: Flavor

A flavor defines the compute, memory, and storage capacity of our instance.

  • Choose the most appropriate sizing for your use case from a list of pre-selected resources
Note: if your instance does not boot up, you may need to increase your flavor’s resources.
Note: If you don’t see a list of flavors contact; instances are added based on your project needs.


  • click Next when done to go to the Networks screen.

Step 4: Network & Network Ports

  • Select a project network, which determines routability of either a public/internet or campus/internal floating IP.
  • click Next when done to go to the Ports screen.
    • Ports provide extra communication channels to your instances.
    • You can select ports instead of networks or a mix of both.


  • click Next when done to go to the Security Groups screen.

Step 5: Security Groups

Security Groups act as a virtual firewall for your instance to control inbound and outbound traffic. Select the secrity groups to launch the instance in (e.g. ssh-restricted in order to ssh into your vm, icmp to ping your instance).

  • Security groups act at the instance level and can be changed after instance creation.


  • click Next when done to go to the Key Pair screen.

Step 6: Key Pairs

  • A key pair allows you to SSH into your new instance.
  • You may select an existing key pair, import a key pair, or generate a new key pair.
    • Tip: it is often easiest to create a keypair in a terminal on your local machine and import it:

An aside on SSH keypairs: SSH keys are an access credential that is used in the SSH protocol and they are foundational to modern Infrastructure-as-a-Service platforms. Public key authentication provides cryptographic strength that even extremely long passwords can not offer. With SSH, public key authentication improves security considerably as it frees the users from remembering complicated passwords (or worse yet, writing them down).

They can be tricky to set up for new users however, so we’ll go over a simple example here. From your terminal in a local machine use the ssh-keygen command to create a new ssh keypair (you can specify cryptographic algorithm, in this case we’ll use the Ed25519 algorithm):

$ ssh-keygen -t ed25519
Generating public/private ed25519 key pair.
Enter file in which to save the key (/home/username/.ssh/id_ed25519):

Here, you can specify the full path/name of the keypair files and even set a extra passwords. We’ll press enter twice for the no passphrase option. Our new keypairs have been created at /home/username/.ssh/ and are called id_ed25519 and The public key (.pub) can be transferred to other remote servers (this is the key we will import to our CUmulus instance), but the private key (no suffix) should never leave the host machine.


  • click Next when done to go to the Configuration screen.

Step 7: Configuration, Server Group, Scheduler Hints, and Metadata

  • For the remaining screens – Configuration, Server Group, Scheduler Hints, and Metadata – leave these as defaults, as they are extra, optional configuration for the instances.


Step 9: Launch the instance

Your instance will take a few minutes to finish provisioning. Once it’s finished, your instance will be available from the “Instance” sub-tab.

Step 10: (Optional) Associate Floating IP to instance

  • You can now associate a Floating IP to enable access to the instance from outside of the CU network.
    • On the right hand side of the newly created instance, choose Associate Floating IP under the Actions dropdown


  • Now, select from available IP addresses if needed (e.g., if you’ll be adding a web portal to your instance)
  • The Select port to be associated option should already be pre-populated with the internal IP of your new instance. Click associate.


Associate the IP Address to your instance

Note: If an instance is terminated, the floating IP will be disassociated but remain with the project as an available address. If the floating IP is it is returned to the SN IP pool and can be difficult to re-allocate if the same address is desired.

Step 11: Logging into your Instance

At a minimum, you’ll need to login to your instance via ssh to install the software you’ll be using. Other reasons to login to the instance include to stop or start services, associate a domain name with your IP, run your software, troubleshoot problems, etc. You are essentially the “system administrator” of your own instance.

  • To login to an instance via ssh, you must be on CU VPN to connect (this is CURC restriction).
  • If you are not a CU Boulder user (and therefore do not have VPN access), please follow the instructions provided here to spawn a terminal through Open OnDemand. You can use this terminal to login to an instance via ssh.
  • Open up an ssh connection providing the identity (key) file that you associated with the instance in the Key Pair step covered earlier:
$ ssh -i ~/.ssh/<private key> <hostname>@<external floating IP>
  • Note that hostname will be “ubuntu” for Ubuntu instances, “centos” for Centos instances, etc.
    • For example, for an ubuntu instance your ssh command may look something like this:
$ ssh -i ~/.ssh/testkey ubuntu@123.456.789.123

If desired, set a password on the root account to simplify troubleshooting (via the recovery console) if the instance loses network connectivity.

$ sudo su - 
$ passwd root

Get the default DNS name (optional)

  1. All Floating IP’s have a default A record. This can optionally be used in place of an IP address.

  2. Perform a reverse lookup:


  3. If a specific record is desired, contact NEO via


  • If no available addresses are allocated to the project, you can allocate one by clicking the “+” button:


  • Depending on which network was selected in Step 4, allocate either an public/internet floating IP, (scinet-external) or a campus internal floating IP. (scinet-internal)