2.0: jupyterlab by default

swaps from default nbclassic and opt-in to lab, to now default to lab and opt-in to nbclassic

defaults to jupyterlab *if* lab 3.1 is available,
so should still work without configuration if lab is unavailable (or too old)

.github/workflows/test.yml

@@ -38,9 +38,9 @@ jobs:
         #   Tests everything when JupyterHub works against a dedicated mysql or
         #   postgresql server.
         #
-        # jupyter_server:
+        # nbclassic:
         #   Tests everything when the user instances are started with
-        #   jupyter_server instead of notebook.
+        #   notebook instead of jupyter_server.
         #
         # ssl:
         #   Tests everything using internal SSL connections instead of
@@ -48,7 +48,7 @@ jobs:
         #
         # main_dependencies:
         #   Tests everything when the we use the latest available dependencies
-        #   from: ipytraitlets.
+        #   from: traitlets.
         #
         # NOTE: Since only the value of these parameters are presented in the
         #       GitHub UI when the workflow run, we avoid using true/false as
@@ -56,6 +56,7 @@ jobs:
         include:
           - python: "3.6"
             oldest_dependencies: oldest_dependencies
+            nbclassic: nbclassic
           - python: "3.6"
             subdomain: subdomain
           - python: "3.7"
@@ -65,7 +66,7 @@ jobs:
           - python: "3.8"
             db: postgres
           - python: "3.8"
-            jupyter_server: jupyter_server
+            nbclassic: nbclassic
           - python: "3.9"
             main_dependencies: main_dependencies
 
@@ -130,9 +131,9 @@ jobs:
           if [ "${{ matrix.main_dependencies }}" != "" ]; then
               pip install git+https://github.com/ipython/traitlets#egg=traitlets --force
           fi
-          if [ "${{ matrix.jupyter_server }}" != "" ]; then
-              pip uninstall notebook --yes
-              pip install jupyter_server
+          if [ "${{ matrix.nbclassic }}" != "" ]; then
+              pip uninstall jupyter_server --yes
+              pip install notebook
           fi
           if [ "${{ matrix.db }}" == "mysql" ]; then
               pip install mysql-connector-python

dev-requirements.txt

@@ -7,8 +7,8 @@ codecov
 coverage
 cryptography
 html5lib  # needed for beautifulsoup
+jupyterlab >=3
 mock
-notebook
 pre-commit
 pytest>=3.3
 pytest-asyncio

docs/source/reference/config-user-env.md

@@ -76,13 +76,26 @@ c.InteractiveShellApp.extensions.append("cython")
 
 ### Example: Enable a Jupyter notebook configuration setting for all users
 
+:::{note}
+These examples configure the Jupyter ServerApp,
+which is used by JupyterLab, the default in JupyterHub 2.0.
+
+If you are using the classing Jupyter Notebook server,
+the same things should work,
+with the following substitutions:
+
+- Where you see `jupyter_server_config`, use `jupyter_notebook_config`
+- Where you see `NotebookApp`, use `ServerApp`
+
+:::
+
 To enable Jupyter notebook's internal idle-shutdown behavior (requires
-notebook ≥ 5.4), set the following in the `/etc/jupyter/jupyter_notebook_config.py`
+notebook ≥ 5.4), set the following in the `/etc/jupyter/jupyter_server_config.py`
 file:
 
 ```python
 # shutdown the server after no activity for an hour
-c.NotebookApp.shutdown_no_activity_timeout = 60 * 60
+c.ServerApp.shutdown_no_activity_timeout = 60 * 60
 # shutdown kernels after no activity for 20 minutes
 c.MappingKernelManager.cull_idle_timeout = 20 * 60
 # check for idle kernels every two minutes
@@ -112,8 +125,8 @@ Assuming I have a Python 2 and Python 3 environment that I want to make
 sure are available, I can install their specs system-wide (in /usr/local) with:
 
 ```bash
-/path/to/python3 -m IPython kernel install --prefix=/usr/local
-/path/to/python2 -m IPython kernel install --prefix=/usr/local
+/path/to/python3 -m ipykernel install --prefix=/usr/local
+/path/to/python2 -m ipykernel install --prefix=/usr/local
 ```
 
 ## Multi-user hosts vs. Containers
@@ -176,12 +189,38 @@ The number of named servers per user can be limited by setting
 c.JupyterHub.named_server_limit_per_user = 5
 ```
 
-## Switching to Jupyter Server
+## Switching back to classic notebook
 
-[Jupyter Server](https://jupyter-server.readthedocs.io/en/latest/) is a new Tornado Server backend for Jupyter web applications (e.g. JupyterLab 3.0 uses this package as its default backend).
+By default the single-user server launches JupyterLab,
+which is based on [Jupyter Server][].
+This is the default server when running JupyterHub ≥ 2.0.
+You can switch to using the legacy Jupyter Notebook server by setting the `JUPYTERHUB_SINGLEUSER_APP` environment variable
+(in the single-user environment) to:
 
-By default, the single-user notebook server uses the (old) `NotebookApp` from the [notebook](https://github.com/jupyter/notebook) package. You can switch to using Jupyter Server's `ServerApp` backend (this will likely become the default in future releases) by setting the `JUPYTERHUB_SINGLEUSER_APP` environment variable to:
+```bash
+export JUPYTERHUB_SINGLEUSER_APP='notebook.notebookapp.NotebookApp'
+```
+
+[jupyter server]: https://jupyter-server.readthedocs.io
+[jupyter notebook]: https://jupyter-notebook.readthedocs.io
+
+:::{versionchanged} 2.0
+JupyterLab is now the default singleuser UI, if available,
+which is based on the [Jupyter Server][],
+no longer the legacy [Jupyter Notebook][] server.
+JupyterHub prior to 2.0 launched the legacy notebook server (`jupyter notebook`),
+and Jupyter server could be selected by specifying
+
+```python
+# jupyterhub_config.py
+c.Spawner.cmd = ["jupyter-labhub"]
+```
+
+or for an otherwise customized Jupyter Server app,
+set the environment variable:
 
 ```bash
 export JUPYTERHUB_SINGLEUSER_APP='jupyter_server.serverapp.ServerApp'
 ```
+
+:::

jupyterhub/singleuser/app.py

@@ -1,7 +1,12 @@
 """Make a single-user app based on the environment:
 
 - $JUPYTERHUB_SINGLEUSER_APP, the base Application class, to be wrapped in JupyterHub authentication.
-  default: notebook.notebookapp.NotebookApp
+  default: jupyter_server.serverapp.ServerApp
+
+.. versionchanged:: 2.0
+
+    Default app changed to launch `jupyter labhub`.
+    Use JUPYTERHUB_SINGLEUSER_APP=notebook.notebookapp.NotebookApp for the legacy 'classic' notebook server.
 """
 import os
 
@@ -9,12 +14,55 @@ from traitlets import import_item
 
 from .mixins import make_singleuser_app
 
-JUPYTERHUB_SINGLEUSER_APP = (
-    os.environ.get("JUPYTERHUB_SINGLEUSER_APP") or "notebook.notebookapp.NotebookApp"
-)
+JUPYTERHUB_SINGLEUSER_APP = os.environ.get("JUPYTERHUB_SINGLEUSER_APP")
 
+
+if JUPYTERHUB_SINGLEUSER_APP:
     App = import_item(JUPYTERHUB_SINGLEUSER_APP)
+else:
+    App = None
+    _import_error = None
+    for JUPYTERHUB_SINGLEUSER_APP in (
+        "jupyter_server.serverapp.ServerApp",
+        "notebook.notebookapp.NotebookApp",
+    ):
+        try:
+            App = import_item(JUPYTERHUB_SINGLEUSER_APP)
+        except ImportError as e:
+            continue
+            if _import_error is None:
+                _import_error = e
+        else:
+            break
+    if App is None:
+        raise _import_error
+
 
 SingleUserNotebookApp = make_singleuser_app(App)
 
-main = SingleUserNotebookApp.launch_instance
+
+def main():
+    """Launch a jupyterhub single-user server"""
+    if not os.environ.get("JUPYTERHUB_SINGLEUSER_APP"):
+        # app not specified, launch jupyter-labhub by default,
+        # if jupyterlab is recent enough (3.1).
+        # This is a minimally extended ServerApp that does:
+        # 1. ensure lab extension is enabled, and
+        # 2. set default URL to `/lab`
+        import re
+
+        _version_pat = re.compile(r"(\d+)\.(\d+)")
+        try:
+            import jupyterlab
+            from jupyterlab.labhubapp import SingleUserLabApp
+
+            m = _version_pat.match(jupyterlab.__version__)
+        except Exception:
+            m = None
+
+        if m is not None:
+            version_tuple = tuple(int(v) for v in m.groups())
+            if version_tuple >= (3, 1):
+                return SingleUserLabApp.launch_instance()
+
+    return SingleUserNotebookApp.launch_instance()

jupyterhub/tests/test_singleuser.py

@@ -1,6 +1,10 @@
 """Tests for jupyterhub.singleuser"""
+import os
 import sys
+from contextlib import contextmanager
+from subprocess import CalledProcessError
 from subprocess import check_output
+from unittest import mock
 from urllib.parse import urlparse
 
 import pytest
@@ -14,6 +18,12 @@ from .utils import async_requests
 from .utils import AsyncSession
 
 
+@contextmanager
+def nullcontext():
+    """Python 3.7+ contextlib.nullcontext, backport for 3.6"""
+    yield
+
+
 @pytest.mark.parametrize(
     "access_scopes, server_name, expect_success",
     [
@@ -171,3 +181,47 @@ def test_version():
         [sys.executable, '-m', 'jupyterhub.singleuser', '--version']
     ).decode('utf8', 'replace')
     assert jupyterhub.__version__ in out
+
+
+@pytest.mark.parametrize(
+    "JUPYTERHUB_SINGLEUSER_APP",
+    [
+        "",
+        "notebook.notebookapp.NotebookApp",
+        "jupyter_server.serverapp.ServerApp",
+    ],
+)
+def test_singleuser_app_class(JUPYTERHUB_SINGLEUSER_APP):
+    try:
+        import jupyter_server  # noqa
+    except ImportError:
+        have_server = False
+        expect_error = "jupyter_server" in JUPYTERHUB_SINGLEUSER_APP
+    else:
+        have_server = True
+        expect_error = False
+
+    if expect_error:
+        ctx = pytest.raises(CalledProcessError)
+    else:
+        ctx = nullcontext()
+
+    with mock.patch.dict(
+        os.environ,
+        {
+            "JUPYTERHUB_SINGLEUSER_APP": JUPYTERHUB_SINGLEUSER_APP,
+        },
+    ):
+        with ctx:
+            out = check_output(
+                [sys.executable, '-m', 'jupyterhub.singleuser', '--help-all']
+            ).decode('utf8', 'replace')
+    if expect_error:
+        return
+    # use help-all output to check inheritance
+    if 'NotebookApp' in JUPYTERHUB_SINGLEUSER_APP or not have_server:
+        assert '--NotebookApp.' in out
+        assert '--ServerApp.' not in out
+    else:
+        assert '--ServerApp.' in out
+        assert '--NotebookApp.' not in out

singleuser/Dockerfile

@@ -7,6 +7,6 @@ MAINTAINER Project Jupyter <jupyter@googlegroups.com>
 
 ADD install_jupyterhub /tmp/install_jupyterhub
 ARG JUPYTERHUB_VERSION=main
-# install pinned jupyterhub and ensure notebook is installed
+# install pinned jupyterhub and ensure jupyterlab is installed
 RUN python3 /tmp/install_jupyterhub && \
-    python3 -m pip install notebook
+    python3 -m pip install jupyterlab