Technical Overview

JupyterHub is a set of processes that together provide a single user Jupyter Notebook server for each person in a group.

This section gives you an overview of:

JupyterHub's Subsystems: Hub, Proxy, Single-User Notebook Server
how the subsystems interact
the step-by-step events from JupyterHub access to user login

The Subsystems: Hub, Proxy, Single-User Notebook Server

Three major subsystems are started by the jupyterhub command line program:

Hub (Python/Tornado): manages user accounts, authentication, and coordinates Single User Notebook Servers using a Spawner.
Proxy: the public facing part of JupyterHub that uses a dynamic proxy to route HTTP requests to the Hub and Single User Notebook Servers. configurable http proxy (node-http-proxy) is the default proxy.
Single-User Notebook Server (Python/IPython/Tornado): a dedicated, single-user, Jupyter Notebook server is started for each user on the system when the user logs in. The object that starts the single-user notebook servers is called a Spawner.

How the Subsystems Interact

Users access JupyterHub through a web browser, by going to the IP address or the domain name of the server.

The basic principles of operation are:

The Hub spawns proxy
The proxy forwards all requests to the Hub by default
The Hub handles login, and spawns single-user notebook servers on demand
The Hub configures the proxy to forward url prefixes to single-user notebook servers

The proxy is the only process that listens on a public interface. The Hub sits behind the proxy at /hub. Single-user servers sit behind the proxy at /user/[username].

Different authenticators control access to JupyterHub. The default one (PAM) uses the user accounts on the server where JupyterHub is running. If you use this, you will need to create a user account on the system for each user on your team. Using other authenticators, you can allow users to sign in with e.g. a GitHub account, or with any single-sign-on system your organization has.

Next, spawners control how JupyterHub starts the individual notebook server for each user. The default spawner will start a notebook server on the same machine running under their system username. The other main option is to start each server in a separate container, often using Docker.

When user accesses JupyterHub, the following events take place:

Login data is handed to the Authenticator instance for validation
The Authenticator returns the username and if the login information is valid
A single-user notebook server instance is spawned for the logged-in user
When the single-user notebook server starts, the proxy is notified to forward requests to /user/[username]/* to the single-user notebook server.
Two cookies are set, one for /hub/ and another for /user/[username], containing an encrypted token.
The browser is redirected to /user/[username], and the request is handled by the single-user notebook server.

Logging into a single-user notebook server is authenticated via the Hub:

On request, the single-user server forwards the encrypted cookie to the Hub for verification.
The Hub replies with the username if the encrypted cookie is valid.
If the user is the owner of the single-user notebook server, access is allowed.
If it is the wrong user or an invalid cookie, the browser is redirected to /hub/login.

Default behavior

By default, the Proxy listens on all public interfaces on port 8000. Thus you can reach JupyterHub through either:

http://localhost:8000
or any other public IP or domain pointing to your system.

In their default configuration, the other services, the Hub and Single-User Notebook Servers, all communicate with each other on localhost only.

By default, starting JupyterHub will write two files to disk in the current working directory:

jupyterhub.sqlite is the SQLite database containing all of the state of the Hub. This file allows the Hub to remember which users are running and where, as well as storing other information enabling you to restart parts of JupyterHub separately. It is important to note that this database contains no sensitive information other than Hub usernames.
jupyterhub_cookie_secret is the encryption key used for securing cookies. This file needs to persist so that a Hub server restart will avoid invalidating cookies. Conversely, deleting this file and restarting the server effectively invalidates all login cookies. The cookie secret file is discussed in the Cookie Secret section of the Security Basics document.

The location of these files can be specified via configuration settings. It is recommended that these files be stored in standard UNIX filesystem locations, such as /etc/jupyterhub for all configuration files and /srv/jupyterhub for all security and runtime files.

Customizing JupyterHub

There are two basic extension points for JupyterHub:

How users are authenticated
How user's single-user notebook server processes are started

Each is governed by a customizable class, and JupyterHub ships with basic defaults for each.

To enable custom authentication and/or spawning, subclass Authenticator or Spawner, and override the relevant methods.

Authentication

Authentication is customizable via the Authenticator class. Authentication can be replaced by any mechanism, such as OAuth, Kerberos, etc.

JupyterHub only ships with Default PAM, or pluggable authentication module, authentication. This requires the jupyterhub Hub server to be run as root, or at least with access to the PAM service, which regular users typically do not have (e.g. on Ubuntu, this requires being added to the shadow group).

More info on custom Authenticators.

See a list of custom Authenticators on the wiki.

Spawning

Each single-user server is started by a Spawner. The Spawner represents an abstract interface to a process, and needs to be able to take three actions:

start the process
poll whether the process is still running
stop the process

More info on custom Spawners.

See a list of custom Spawners on the wiki.

6.6 KiB Raw Blame History