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Min RK a32986e9cc server-api doc: final touches

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Starting servers with the JupyterHub API

JupyterHub's REST API allows launching servers on behalf of users without ever interacting with the JupyterHub UI. This allows you to build services launching Jupyter-based services for users without relying on the JupyterHub UI at all, enabling a variety of user/launch/lifecycle patterns not natively supported by JupyterHub, without needing to develop all the server management features of JupyterHub Spawners and/or Authenticators. BinderHub is an example of such an application.

This document provides an example of working with the JupyterHub API to manage servers for users. In particular, we will cover how to:

(checking)=

Checking server status

Requesting information about a user includes a servers field, which is a dictionary.

GET /hub/api/users/:username

Required scope: read:servers

{
  "admin": false,
  "groups": [],
  "pending": null,
  "server": null,
  "name": "test-1",
  "kind": "user",
  "last_activity": "2021-08-03T18:12:46.026411Z",
  "created": "2021-08-03T18:09:59.767600Z",
  "roles": ["user"],
  "servers": {}
}

If the servers dict is empty, the user has no running servers. The keys of the servers dict are server names as strings. Many JupyterHub deployments only use the 'default' server, which has the empty string '' for a name. In this case, the servers dict will always have either zero or one elements.

This is the servers dict when the user's default server is fully running and ready:

  "servers": {
    "": {
      "name": "",
      "last_activity": "2021-08-03T18:48:35.934000Z",
      "started": "2021-08-03T18:48:29.093885Z",
      "pending": null,
      "ready": true,
      "url": "/user/test-1/",
      "user_options": {},
      "progress_url": "/hub/api/users/test-1/server/progress"
    }
  }

Key properties of a server:

name: the server's name. Always the same as the key in servers
ready: boolean. If true, the server can be expected to respond to requests at url.
pending: null or a string indicating a transitional state (such as start or stop). Will always be null if ready is true, and will always be a string if ready is false.
url: The server's url (just the path, e.g. /users/:name/:servername/) where the server can be accessed if ready is true.
progress_url: The API url path (starting with /hub/api) where the progress API can be used to wait for the server to be ready. See below for more details on the progress API.
last_activity: ISO8601 timestamp indicating when activity was last observed on the server
started: ISO801 timestamp indicating when the server was last started

We've seen the servers model with no servers and with one ready server. Here is what it looks like immediately after requesting a server launch, while the server is not ready yet:

  "servers": {
    "": {
      "name": "",
      "last_activity": "2021-08-03T18:48:29.093885Z",
      "started": "2021-08-03T18:48:29.093885Z",
      "pending": "spawn",
      "ready": false,
      "url": "/user/test-1/",
      "user_options": {},
      "progress_url": "/hub/api/users/test-1/server/progress"
    }
  }

Note that ready is false and pending is spawn. This means that the server is not ready (attempting to access it may not work) because it isn't finished spawning yet. We'll get more into that below in waiting for a server.

(starting)=

Starting servers

To start a server, make the request

POST /hub/api/users/:username/servers/[:servername]

Required scope: servers

(omit servername for the default server)

Assuming the request was valid, there are two possible responses:

201 Created: This status code means the launch completed and the server is ready. It should be available at the server's URL immediately.
202 Accepted: This is the more likely response, and means that the server has begun launching, but isn't immediately ready. The server has pending: 'spawn' at this point.

Aside: how quickly JupyterHub responds with 202 Accepted is governed by the slow_spawn_timeout tornado setting.

(waiting)=

Waiting for a server

If you are starting a server via the API, there's a good change you want to know when it's ready. There are two ways to do with:

{ref}Polling the server model <polling>
the {ref}progress API <progress>

(polling)=

Polling the server model

The simplest way to check if a server is ready is to request the user model.

If:

the server name is in the user's servers model, and
servers['servername']['ready'] is true

A Python example, checking if a server is ready:

def server_ready(hub_url, user, server_name="", token):
    r = requests.get(
        f"{hub_url}/hub/api/users/{user}/servers/{server_name}",
        headers={"Authorization": f"token {token}"},
    )
    r.raise_for_status()
    user_model = r.json()
    servers = user_model.get("servers", {})
    if server_name not in servers:
        return False

    server = servers[server_name]
    if server['ready']:
        print(f"Server {user}/{server_name} ready at {server['url']}")
        return True
    else:
        print(f"Server {user}/{server_name} not ready, pending {server['pending']}")
        return False

You can keep making this check until ready is true.

(progress)=

Progress API

The most efficient way to wait for a server to start is the progress API.

The progress URL is available in the server model under progress_url, and has the form /hub/api/users/:user/servers/:servername/progress.

the default server progress can be accessed at :user/servers//progress or :user/server/progress

GET /hub/api/users/:user/servers/:servername/progress

Required scope: read:servers

This is an EventStream API. In an event stream, messages are streamed and delivered on lines of the form:

data: {"progress": 10, "message": "...", ...}

where the line after data: contains a JSON-serialized dictionary. Lines that do not start with data: should be ignored.

progress events have the form:

{
    "progress": 0-100,
    "message": "",
    "ready": True, # or False

}

progress: integer, 0-100
message: string message describing progress stages
ready: present and true only for the last event when the server is ready
url: only present if ready is true; will be the server's url

the progress API can be used even with fully ready servers. If the server is ready, there will only be one event that looks like:

{
  "progress": 100,
  "ready": true,
  "message": "Server ready at /user/test-1/",
  "html_message": "Server ready at <a href=\"/user/test-1/\">/user/test-1/</a>",
  "url": "/user/test-1/"
}

where ready and url are the same as in the server model (ready will always be true).

A typical complete stream from the event-stream API:


data: {"progress": 0, "message": "Server requested"}

data: {"progress": 50, "message": "Spawning server..."}

data: {"progress": 100, "ready": true, "message": "Server ready at /user/test-user/", "html_message": "Server ready at <a href=\"/user/test-user/\">/user/test-user/</a>", "url": "/user/test-user/"}

Here is a Python example for consuming an event stream:

:language: python
:pyobject: event_stream

(stopping)=

Stopping servers

Servers can be stopped with a DELETE request:

DELETE /hub/api/users/:user/servers/[:servername]

Required scope: servers

Like start, delete may not complete immediately. The DELETE request has two possible response codes:

204 Deleted: This status code means the delete completed and the server is fully stopped. It will now be absent from the user servers model.
202 Accepted: Like start, 202 means your request was accepted, but is not yet complete. The server has pending: 'stop' at this point.

Unlike start, there is no progress API for stop. To wait for stop to finish, you must poll the user model and wait for the server to disappear from the user servers model.

:language: python
:pyobject: stop_server

(communicating)=

Communicating with servers

JupyterHub tokens with the the access:servers scope can be used to communicate with servers themselves. This can be the same token you used to launch your service.

Access scopes are new in JupyterHub 2.0.
To access servers in JupyterHub 1.x,
a token must be owned by the same user as the server,
*or* be an admin token if admin_access is enabled.

The URL returned from a server model is the url path suffix, e.g. /user/:name/ to append to the jupyterhub base URL.

For instance, {hub_url}{server_url}, where hub_url would be e.g. http://127.0.0.1:8000 by default, and server_url /user/myname, for a full url of http://127.0.0.1:8000/user/myname.

Python example

The JupyterHub repo includes a complete example in {file}examples/server-api tying all this together.

To summarize the steps:

get user info from /user/:name
the server model includes a ready state to tell you if it's ready
if it's not ready, you can follow up with progress_url to wait for it
if it is ready, you can use the url field to link directly to the running server

The example demonstrates starting and stopping servers via the JupyterHub API, including waiting for them to start via the progress API, as well as waiting for them to stop via polling the user model.

:language: python
:start-at: def event_stream
:end-before: def main

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