Provide better error message when running on unsupported distro

.circleci/config.yml

@@ -57,7 +57,7 @@ jobs:
             - run:
                 name: setup python3
                 command: |
-                    apk add --no-cache python3
+                    apk add --no-cache python3 pytest
 
             - checkout
             - setup_remote_docker
@@ -79,6 +79,12 @@ jobs:
                         --installer-args "--plugin /srv/src/integration-tests/plugins/simplest" \
                         plugins test_simplest_plugin.py
 
+            - run:
+                name: Run distro check test
+                command: |
+                    py.test integration-tests/test_distro.py
+
+
 
     documentation:
         docker:

bootstrap/bootstrap.py

@@ -8,15 +8,24 @@ This script is run as:
     curl <script-url> | sudo python3 -
 
 Constraints:
-  - Be compatible with Python 3.4 (since we support Ubuntu 16.04)
+  - Entire script should be compatible with Python 3.6 (We run on Ubuntu 18.04+)
+  - Script should parse in Python 3.4 (since we exit with useful error message on Ubuntu 14.04+)
   - Use stdlib modules only
 """
 import os
 import subprocess
 import sys
 import logging
+import platform
 
-
+# Support only Ubuntu 18.04+
+distro, version, _ = platform.linux_distribution()
+if distro != 'Ubuntu':
+    print('The Littlest JupyterHub currently supports Ubuntu Linux only')
+    sys.exit(1)
+elif float(version) < 18.04:
+    print('The Littlest JupyterHub requires Ubuntu 18.04 or higher')
+    sys.exit(1)
 
 def main():
     install_prefix = os.environ.get('TLJH_INSTALL_PREFIX', '/opt/tljh')

docs/index.rst

@@ -6,6 +6,7 @@ A simple `JupyterHub <https://github.com/jupyterhub/jupyterhub>`_ distribution f
 a small (0-100) number of users on a single server. We recommend reading
 :ref:`topic/whentouse` to determine if this is the right tool for you.
 
+
 Development Status
 ==================
 
@@ -18,7 +19,8 @@ Installation
 ============
 
 The Littlest JupyterHub (TLJH) can run on any server that is running at least
-Ubuntu 18.04. We have a bunch of tutorials to get you started.
+**Ubuntu 18.04**. Earlier versions of Ubuntu are not supported.
+We have a bunch of tutorials to get you started.
 
 - Tutorials to create a new server from scratch on a cloud provider & run TLJH
   on it. These are **recommended** if you do not have much experience setting up

integration-tests/test_distro.py

@@ -0,0 +1,40 @@
+"""
+Test running on non-supported distros
+"""
+import subprocess
+
+def test_ubuntu_too_old():
+    container_name = 'old-distro-test'
+
+    # stop container if it is already running
+    subprocess.run([
+        'docker', 'rm', '-f', container_name
+    ])
+    
+    # Start a detached Ubuntu 16.04 container
+    subprocess.check_call([
+        'docker', 'run', '--detach', '--name', container_name, 'ubuntu:16.04', 
+        '/bin/bash', '-c', 'sleep 1000s'
+    ])
+    # Install python3 inside the ubuntu container
+    # There is no trusted Ubuntu+Python3 container we can use
+    subprocess.check_output([
+        'docker', 'exec', container_name, 'apt-get', 'update'
+    ])
+    subprocess.check_output([
+        'docker', 'exec', container_name, 'apt-get', 'install', '--yes', 'python3'
+    ])
+    # Copy only the bootstrap script  to container, so this is faster
+    subprocess.check_call([
+        'docker',
+        'cp',
+        'bootstrap/', f'{container_name}:/srv'
+    ])
+
+    # Run bootstrap script, validate that it fails appropriately
+    output = subprocess.run([
+        'docker', 'exec', '-i', container_name,
+        'python3', '/srv/bootstrap/bootstrap.py'
+    ], check=False, stdout=subprocess.PIPE, encoding='utf-8')
+    assert output.stdout == 'The Littlest JupyterHub requires Ubuntu 18.04 or higher\n'
+    assert output.returncode == 1