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 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
nullor a string indicating a transitional state (such asstartorstop). Will always benullifreadyis true, and will always be a string ifreadyis false.- url
The server’s url (just the path, e.g.
/users/:name/:servername/) where the server can be accessed ifreadyis 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 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 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:
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
serversmodel, andservers['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 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
readyis 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:
def event_stream(session, url):
"""Generator yielding events from a JSON event stream
For use with the server progress API
"""
r = session.get(url, stream=True)
r.raise_for_status()
for line in r.iter_lines():
line = line.decode('utf8', 'replace')
# event lines all start with `data:`
# all other lines should be ignored (they will be empty)
if line.startswith('data:'):
yield json.loads(line.split(':', 1)[1])
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
serversmodel.- 202 Accepted
Like start,
202means your request was accepted, but is not yet complete. The server haspending: '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.
def stop_server(session, hub_url, user, server_name=""):
"""Stop a server via the JupyterHub API
Returns when the server has finished stopping
"""
# step 1: get user status
user_url = f"{hub_url}/hub/api/users/{user}"
server_url = f"{user_url}/servers/{server_name}"
log_name = f"{user}/{server_name}".rstrip("/")
log.info(f"Stopping server {log_name}")
r = session.delete(server_url)
if r.status_code == 404:
log.info(f"Server {log_name} already stopped")
r.raise_for_status()
if r.status_code == 204:
log.info(f"Server {log_name} stopped")
return
# else: 202, stop requested, but not complete
# wait for stop to finish
log.info(f"Server {log_name} stopping...")
# wait for server to be done stopping
while True:
r = session.get(user_url)
r.raise_for_status()
user_model = r.json()
if server_name not in user_model.get("servers", {}):
log.info(f"Server {log_name} stopped")
return
server = user_model["servers"][server_name]
if not server['pending']:
raise ValueError(f"Waiting for {log_name}, but no longer pending.")
log.info(f"Server {log_name} pending: {server['pending']}")
# wait to poll again
time.sleep(1)
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.
Note
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 examples/server-api
tying all this together.
To summarize the steps:
get user info from
/user/:namethe server model includes a
readystate to tell you if it’s readyif it’s not ready, you can follow up with
progress_urlto wait for itif it is ready, you can use the
urlfield 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.
def event_stream(session, url):
"""Generator yielding events from a JSON event stream
For use with the server progress API
"""
r = session.get(url, stream=True)
r.raise_for_status()
for line in r.iter_lines():
line = line.decode('utf8', 'replace')
# event lines all start with `data:`
# all other lines should be ignored (they will be empty)
if line.startswith('data:'):
yield json.loads(line.split(':', 1)[1])
def start_server(session, hub_url, user, server_name=""):
"""Start a server for a jupyterhub user
Returns the full URL for accessing the server
"""
user_url = f"{hub_url}/hub/api/users/{user}"
log_name = f"{user}/{server_name}".rstrip("/")
# step 1: get user status
r = session.get(user_url)
r.raise_for_status()
user_model = r.json()
# if server is not 'active', request launch
if server_name not in user_model.get('servers', {}):
log.info(f"Starting server {log_name}")
r = session.post(f"{user_url}/servers/{server_name}")
r.raise_for_status()
if r.status_code == 201:
log.info(f"Server {log_name} is launched and ready")
elif r.status_code == 202:
log.info(f"Server {log_name} is launching...")
else:
log.warning(f"Unexpected status: {r.status_code}")
r = session.get(user_url)
r.raise_for_status()
user_model = r.json()
# report server status
server = user_model['servers'][server_name]
if server['pending']:
status = f"pending {server['pending']}"
elif server['ready']:
status = "ready"
else:
# shouldn't be possible!
raise ValueError(f"Unexpected server state: {server}")
log.info(f"Server {log_name} is {status}")
# wait for server to be ready using progress API
progress_url = user_model['servers'][server_name]['progress_url']
for event in event_stream(session, f"{hub_url}{progress_url}"):
log.info(f"Progress {event['progress']}%: {event['message']}")
if event.get("ready"):
server_url = event['url']
break
else:
# server never ready
raise ValueError(f"{log_name} never started!")
# at this point, we know the server is ready and waiting to receive requests
# return the full URL where the server can be accessed
return f"{hub_url}{server_url}"
def stop_server(session, hub_url, user, server_name=""):
"""Stop a server via the JupyterHub API
Returns when the server has finished stopping
"""
# step 1: get user status
user_url = f"{hub_url}/hub/api/users/{user}"
server_url = f"{user_url}/servers/{server_name}"
log_name = f"{user}/{server_name}".rstrip("/")
log.info(f"Stopping server {log_name}")
r = session.delete(server_url)
if r.status_code == 404:
log.info(f"Server {log_name} already stopped")
r.raise_for_status()
if r.status_code == 204:
log.info(f"Server {log_name} stopped")
return
# else: 202, stop requested, but not complete
# wait for stop to finish
log.info(f"Server {log_name} stopping...")
# wait for server to be done stopping
while True:
r = session.get(user_url)
r.raise_for_status()
user_model = r.json()
if server_name not in user_model.get("servers", {}):
log.info(f"Server {log_name} stopped")
return
server = user_model["servers"][server_name]
if not server['pending']:
raise ValueError(f"Waiting for {log_name}, but no longer pending.")
log.info(f"Server {log_name} pending: {server['pending']}")
# wait to poll again
time.sleep(1)