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166 lines
6.8 KiB
Markdown
166 lines
6.8 KiB
Markdown
# Technical Overview
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JupyterHub is a set of processes that together provide a single user Jupyter
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Notebook server for each person in a group.
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This section gives you an overview of:
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- JupyterHub's subsystems
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- basic operations
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- logging in
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-
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## Subsystems of JupyterHub
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Three major subsystems are started by the `jupyterhub` command line program:
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- **Hub** (Python/Tornado): manages user accounts, authentication, and
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coordinates Single User Notebook Servers using a Spawner.
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- **Proxy**: the public facing part of JupyterHub that uses a dynamic proxy
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to route HTTP requests to the Hub and Single User Notebook Servers.
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[configurable http proxy](https://github.com/jupyterhub/configurable-http-proxy)
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(node-http-proxy) is the default proxy.
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- **Single-User Notebook Server** (Python/IPython/Tornado): a dedicated,
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single-user, Jupyter Notebook server is started for each user on the system
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when the user logs in. The object that starts the single-user notebook
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servers is called a **Spawner**.
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## Basic operation
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Users access JupyterHub through a web browser, by going to the IP address or
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the domain name of the server.
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The basic principles of operation are:
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- The Hub spawns proxy
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- The proxy forwards all requests to the Hub by default
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- The Hub handles login, and spawns single-user notebook servers on demand
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- The Hub configures the proxy to forward url prefixes to single-user notebook
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servers
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The proxy is the only process that listens on a public interface. The Hub sits
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behind the proxy at `/hub`. Single-user servers sit behind the proxy at
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`/user/[username]`.
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Different **[authenticators](authenticators.html)** control access
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to JupyterHub. The default one (PAM) uses the user accounts on the server where
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JupyterHub is running. If you use this, you will need to create a user account
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on the system for each user on your team. Using other authenticators, you can
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allow users to sign in with e.g. a GitHub account, or with any single-sign-on
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system your organization has.
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Next, **[spawners](spawners.html)** control how JupyterHub starts
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the individual notebook server for each user. The default spawner will
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start a notebook server on the same machine running under their system username.
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The other main option is to start each server in a separate container, often
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using Docker.
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## Logging in
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When a new browser logs in to JupyterHub, the following events take place:
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- Login data is handed to the [Authenticator](#authentication) instance for validation
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- The Authenticator returns the username, if login information is valid
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- A single-user server instance is [Spawned](#spawning) for the logged-in user
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- When the server starts, the proxy is notified to forward `/user/[username]/*` to the single-user server
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- Two cookies are set, one for `/hub/` and another for `/user/[username]`,
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containing an encrypted token.
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- The browser is redirected to `/user/[username]`, which is handled by the single-user server
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Logging into a single-user server is authenticated via the Hub:
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- On request, the single-user server forwards the encrypted cookie to the Hub for verification
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- The Hub replies with the username if it is a valid cookie
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- If the user is the owner of the server, access is allowed
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- If it is the wrong user or an invalid cookie, the browser is redirected to `/hub/login`
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## Customizing JupyterHub
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There are two basic extension points for JupyterHub: How users are authenticated,
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and how their server processes are started.
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Each is governed by a customizable class,
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and JupyterHub ships with just the most basic version of each.
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To enable custom authentication and/or spawning,
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subclass Authenticator or Spawner,
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and override the relevant methods.
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## Default behavior
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**IMPORTANT: You should not run JupyterHub without SSL encryption on a public network.**
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See [Security documentation](#security) for how to configure JupyterHub to use SSL,
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or put it behind SSL termination in another proxy server, such as nginx.
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To start JupyterHub in its default configuration, type the following at the command line:
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```bash
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sudo jupyterhub
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```
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The default Authenticator that ships with JupyterHub authenticates users
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with their system name and password (via [PAM][]).
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Any user on the system with a password will be allowed to start a single-user notebook server.
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The default Spawner starts servers locally as each user, one dedicated server per user.
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These servers listen on localhost, and start in the given user's home directory.
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By default, the **Proxy** listens on all public interfaces on port 8000.
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Thus you can reach JupyterHub through either:
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- `http://localhost:8000`
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- or any other public IP or domain pointing to your system.
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In their default configuration, the other services, the **Hub** and **Single-User Servers**,
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all communicate with each other on localhost only.
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By default, starting JupyterHub will write two files to disk in the current working directory:
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- `jupyterhub.sqlite` is the sqlite database containing all of the state of the **Hub**.
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This file allows the **Hub** to remember what users are running and where,
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as well as other information enabling you to restart parts of JupyterHub separately. It is
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important to note that this database contains *no* sensitive information other than **Hub**
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usernames.
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- `jupyterhub_cookie_secret` is the encryption key used for securing cookies.
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This file needs to persist in order for restarting the Hub server to avoid invalidating cookies.
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Conversely, deleting this file and restarting the server effectively invalidates all login cookies.
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The cookie secret file is discussed in the [Cookie Secret documentation](#cookie-secret).
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The location of these files can be specified via configuration.
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[PAM]: https://en.wikipedia.org/wiki/Pluggable_authentication_module
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### Authentication
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Authentication is customizable via the Authenticator class.
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Authentication can be replaced by any mechanism,
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such as OAuth, Kerberos, etc.
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JupyterHub only ships with [PAM](https://en.wikipedia.org/wiki/Pluggable_authentication_module) authentication,
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which requires the server to be run as root,
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or at least with access to the PAM service,
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which regular users typically do not have
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(on Ubuntu, this requires being added to the `shadow` group).
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[More info on custom Authenticators](authenticators.html).
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See a list of custom Authenticators [on the wiki](https://github.com/jupyterhub/jupyterhub/wiki/Authenticators).
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### Spawning
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Each single-user server is started by a Spawner.
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The Spawner represents an abstract interface to a process,
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and needs to be able to take three actions:
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1. start the process
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2. poll whether the process is still running
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3. stop the process
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[More info on custom Spawners](spawners.html).
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See a list of custom Spawners [on the wiki](https://github.com/jupyterhub/jupyterhub/wiki/Spawners).
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