External services

When working with JupyterHub, a Service is defined as a process that interacts with the Hub’s REST API. A Service may perform a specific action or task. For example, shutting down individuals’ single user notebook servers that have been idle for some time is a good example of a task that could be automated by a Service. Let’s look at how the jupyterhub_idle_culler script can be used as a Service.

Real-world example to cull idle servers

JupyterHub has a REST API that can be used by external services. This document will:

• explain some basic information about API tokens

• clarify that API tokens can be used to authenticate to single-user servers as of version 0.8.0

• show how the jupyterhub_idle_culler script can be:

  • used in a Hub-managed service

  • run as a standalone script

Both examples for jupyterhub_idle_culler will communicate tasks to the Hub via the REST API.

API Token basics

Step 1: Generate an API token

To run such an external service, an API token must be created and provided to the service.

As of version 0.6.0, the preferred way of doing this is to first generate an API token:

openssl rand -hex 32

In version 0.8.0, a TOKEN request page for generating an API token is available from the JupyterHub user interface:

Step 2: Pass environment variable with token to the Hub

In the case of cull_idle_servers, it is passed as the environment variable called JUPYTERHUB_API_TOKEN.

Step 3: Use API tokens for services and tasks that require external access

While API tokens are often associated with a specific user, API tokens can be used by services that require external access for activities that may not correspond to a specific human, e.g. adding users during setup for a tutorial or workshop. Add a service and its API token to the JupyterHub configuration file, jupyterhub_config.py:

c.JupyterHub.services = [
    {'name': 'adding-users', 'api_token': 'super-secret-token'},
]

Step 4: Restart JupyterHub

Upon restarting JupyterHub, you should see a message like below in the logs:

Adding API token for <username>

Authenticating to single-user servers using API token

In JupyterHub 0.7, there is no mechanism for token authentication to single-user servers, and only cookies can be used for authentication. 0.8 supports using JupyterHub API tokens to authenticate to single-user servers.

How to configure the idle culler to run as a Hub-Managed Service

Step 1: Install the idle culler:

pip install jupyterhub-idle-culler

Step 2: In jupyterhub_config.py, add the following dictionary for the idle-culler Service to the c.JupyterHub.services list:

c.JupyterHub.services = [
    {
        'name': 'idle-culler',
        'command': [sys.executable, '-m', 'jupyterhub_idle_culler', '--timeout=3600'],
    }
]

c.JupyterHub.load_roles = [
    {
        "name": "list-and-cull", # name the role
        "services": [
            "idle-culler", # assign the service to this role
        ],
        "scopes": [
            # declare what permissions the service should have
            "list:users", # list users
            "read:users:activity", # read user last-activity
            "admin:servers", # start/stop servers
        ],
    }
]

where:

• command indicates that the Service will be launched as a subprocess, managed by the Hub.

Changed in version 2.0: Prior to 2.0, the idle-culler required ‘admin’ permissions. It now needs the scopes:

• list:users to access the user list endpoint

• read:users:activity to read activity info

• admin:servers to start/stop servers

How to run cull-idle manually as a standalone script

Now you can run your script by providing it the API token and it will authenticate through the REST API to interact with it.

This will run the idle culler service manually. It can be run as a standalone script anywhere with access to the Hub, and will periodically check for idle servers and shut them down via the Hub’s REST API. In order to shutdown the servers, the token given to cull-idle must have permission to list users and admin their servers.

Generate an API token and store it in the JUPYTERHUB_API_TOKEN environment variable. Run jupyterhub_idle_culler manually.

    export JUPYTERHUB_API_TOKEN='token'
    python -m jupyterhub_idle_culler [--timeout=900] [--url=http://127.0.0.1:8081/hub/api]