Images contain the information needed to install an operating system on a cloud instance, with all of the correct dependencies and additional programs needed to interact with the rest of the cloud infrastructure. These are different to just a copy of an operating system that is entirely blank; as an image contains a file structure, software and other non-factory setting configuration on it. For example, the catalyst Ubuntu_18.04 image contains a version of Git installed on it once it is started up. Other programs such as a base version of python are also installed.
This allow you as a user to pick an image that most accurately resembles what you are wanting to have for your instance. This also saves you having to install additional software or setting up file structures etc. You are also able to make your own ‘snapshots’ from instances that you run, which you can then save and use as images of your own in the future, this is discussed later in this section.
Additionally, you are able to upload your own images to your project to save time rebuilding any instances that you may have had previously. This is discussed further in this section. For our default images, we ensure that they are accurate to their upstream counterparts by downloading and validating them using a checksum from their sources.