Compute

This component, based on the OpenStack Nova Service, allows the management of the computing resources.

Instances

An instance (or virtual machine) is a software-based emulation of a physical computer. It runs an operating system and applications, just like a physical computer. With instances, users can run applications and workloads in the cloud. Instances can be created from an image, or from a snapshot.

In the corresponding part of the OpenStack Horizon dashboard “Compute → Instances”, you can:

  • visualize the quota of the selected project and its usage in the “Overview” page

  • access the list of instances

  • create a new instance

  • perform operations (Actions) on the selected instance, like attaching/de-attaching volumes, suspend or shut off, creation of snapshots

Virtual machines can be of two types:

Ephemeral Virtual Machines are booted from an OpenStack image.

These images have fixed root volume dimension, dictated from the used flavor.

Creating an ephemeral virtual machine is more lightweight for tenant resources, since the root volume won’t be accounted on the tenant storage quota.

Bootable Virtual Machines are created using a pre-existing volume as root volume.

Users can choose freely the size of the root volume of the virtual machine. Creating a virtual machine from a bootable volume has two main advantages:

  • customizable root volume size

  • the data of the root volume won’t be deleted when deleting the instance

Note

Instance affinity and anti-affinity groups In some cases, users might want to be sure two or more instances run specifically on the same hypervisor (e.g. for ensuring better communication) or on different ones (e.g. to implement high availability). In OpenStack, it is possible to create affinity or anti-affinity groups for this purpose. When creating an instance, it is possible to define whether this will be part of one of the groups available in the tenant.

Key Pairs

Key Pairs are a method for securing SSH access to instances by using public-key cryptography. When a Key Pair is associated with an instance, it allows users to SSH into the instance securely without using a password. This ensures a higher level of security compared to traditional password-based access.

Public-Key Cryptography is a cryptographic system that uses pairs of keys - public keys (which can be shared) and private keys (which are kept secret). The public key is used to encrypt data, and the private key is used to decrypt it. The public key is injected into the instance at the time of creation. The private key is kept by the user and used to establish an SSH connection to the instance.

Image Snapshots

A snapshot is a point-in-time copy of data capturing the current state of a virtual machine. It preserves the state and the data of the VM including its power state (on, off, or suspended) and all its files (such as disks, memory, and network interfaces). Snapshots are generally used to restore a VM after a system failure, bad update, or error.

You can find instances snapshots under the “Compute → Images” section in the Horizon Dashboard.

Warning

  • Before taking a snapshot, log in to the virtual machine and shutdown the instance.

  • Snapshots are stored on the same cloud infrastructure of the instances, but can be downloaded to be stored at a different location.

Images

An image is a template which contains a specific operating system and pre-installed software.

Images hosted on the cloud platform have the “visibility” attribute which can assume 4 different values that define which users can use the image for the instance creation and provides information about who uploaded the image.

Visibility

Characteristics

Public

  • Uploaded only by CINECA HPC Cloud infrastructure administrators.

  • Usable by all the users on the cloud platform and appears in the default image list.

Private

  • Uploaded by any user on the cloud platform (image owner).

  • Usable only by the image owner.

Shared

  • Uploaded by any user on the cloud platform (image owner).

  • By default, usable only by all the users which work on the same project of the image owner.

  • The image owner can explicitly chose a user or a group of users to share the image to: the user or the group of user have to accept the sharing.

Community

  • Uploaded by any user on the cloud platform (image owner).

  • Usable by all the users on the cloud platform and appears in the default image list.

Warning

Since no control can be performed on Community images by the CINECA HPC Cloud infrastructure administrators, Community images are inhibited. Trying to upload a Community image will results in a blocking error both from Horizon dashboard and OpenStack CLI.

Default images for common operating systems are provided by CINECA and available to be used. The updated list of all the images uploaded by CINECA HPC Cloud infrastructure administrators on each HPC cloud infrastructure can be found in the systems specifics pages at Cloud Specifics.