This article is to help enhance your ability to do interactive analyses - with a deeper understanding of key components (i.e. Billing Projects) in Terra's notebooks environment.

A second article addresses key operations and how they impact your work, including how to avoid losing data and overwriting notebook edits when collaborating in a shared workspace.

Glossary of Key Components

Terra provides infrastructure for running and writing Jupyter Notebooks, which are files that contain analysis code and embedded documentation. This section  defines terms, and explains where notebook files and their output live -- when you are working with the files and when you are not.

• Jupyter Kernel
• Notebook Service (Leonardo)
• Compute Engine VM
• Persistent Disk
• Docker
• Cloud Storage
• Dataproc Cluster

Jupyter Kernel

The Jupyter Kernel is the computer program that runs while you have a notebook open. The kernel process maintains the runtime state of the Jupyter notebook.

Terra supports R and Python kernels. When cells in the notebook are executed, they are interpreted by this language-specific kernel. You select the Jupyter kernel when you create a notebook.

Note about accessing analysis output: Until you save a notebook, the output is stored in the kernel only and will be deleted if you stop the kernel before saving. Additionally, even if you save a notebook, the output, which is attached to the kernel, will be lost if you delete or reconfigure the kernel.

Notebook Service

The Notebook Service manages the compute environment you use to edit and run your notebook. In Terra, the notebook service is "Leonardo," and the two terms are often used interchangeably.

Notebook Cluster (aka Compute Engine VM)

When you interact with your notebook in a web browser on your own computer, the characters you type and code you execute are all sent to the Jupyter Kernel process running on a Google Compute Engine virtual machine (VM) or cluster. Much of the discussion in this document involves understanding the Compute Engine VM as a host for your notebooks.

In the rest of this article, your "notebook VM" refers to the Compute Engine VM that hosts your notebooks.

When you create your notebook environment, by default you create a single VM. However, the Terra environment supports more powerful clusters of VMs using Google Cloud Dataproc. Use of a VM cluster is an advanced topic that is outside of the scope of this document.

Persistent Disk

A virtual machine needs a disk for storing data files, the operating system, or other software. The name of Google Compute Engine's block storage is Persistent Disk. It is called "persistent" because the disk itself can persist independent of the VM to which it is attached.

Docker

Docker is a (branded) container technology for packaging software for rapid deployment onto a machine. The Docker container is like a sandboxed virtual machine that exists wholly inside the Compute Engine Virtual Machine. Software and tools for the Terra notebook environment are packaged together and can be deployed on a compute environment in a Docker container.

The ability to create custom Dockers is not yet a feature on Terra: all notebooks run a default Docker configured for genomics computation.

Cloud Storage

Every Terra Workspace has an associated Google Cloud Storage bucket for long-term storage of notebooks and other files. Notebook files (and only notebook files) are automatically saved to your workspace bucket (see section on Saving Notebooks below). You can save other files (such as output files from batch processing) to your workspace bucket manually (see this article for more details on how to do this). 

Persistent Disk versus Cloud Storage

The terminology "persistent disk" can create confusion: Just how persistent are they? Is there something truly special about this persistence? The term "persistent disk" originates from the early days of Google Compute Engine when the disks associated with VMs lived and died along with the VM. When disks were added that could live independent of a VM, the persistence was particularly noteworthy.

Note that if you want to use it, a persistent disk still must be associated with a running VM. This is different from a Cloud Storage bucket, which exists as a point of storage that can be accessed, using APIs, without a VM. 

Multiple Billing Projects

Cloud resources, such as Cloud Storage Buckets and Compute Engine instances exist within Google Cloud Projects. Within Terra, these are referred to as "Billing Projects".

Notebooks belong to workspaces and workspaces belong to Billing Projects.

Thus if you have workspaces in two different billing projects, and you work in notebooks in those two different billing projects, you will have separate Compute Engine resources (see below):