Merge pull request #4714 from meeseeksmachine/auto-backport-of-pr-456…

…1-on-4.x

Backport PR #4561 on branch 4.x (Improve debugging when waiting for servers)

jupyterhub/proxy.py

@@ -49,7 +49,7 @@
 from . import utils
 from .metrics import CHECK_ROUTES_DURATION_SECONDS, PROXY_POLL_DURATION_SECONDS
 from .objects import Server
-from .utils import AnyTimeoutError, exponential_backoff, url_escape_path, url_path_join
+from .utils import exponential_backoff, url_escape_path, url_path_join
 
 
 def _one_at_a_time(method):
@@ -767,24 +767,67 @@ async def start(self):
 
         self._write_pid_file()
 
-        def _check_process():
-            status = self.proxy_process.poll()
-            if status is not None:
-                with self.proxy_process:
-                    e = RuntimeError("Proxy failed to start with exit code %i" % status)
-                    raise e from None
-
-        for server in (public_server, api_server):
-            for i in range(10):
-                _check_process()
-                try:
-                    await server.wait_up(1)
-                except AnyTimeoutError:
-                    continue
-                else:
-                    break
-            await server.wait_up(1)
-        _check_process()
+        async def wait_for_process():
+            """Watch proxy process for early termination
+
+            Runs forever, checking every 0.5s if the process has exited
+            so we don't keep waiting for endpoints after the proxy has stopped.
+
+            Raises RuntimeError if/when the proxy process exits,
+            otherwise runs forever.
+            Should be cancelled when servers become ready.
+            """
+            while True:
+                status = self.proxy_process.poll()
+                if status is not None:
+                    with self.proxy_process:
+                        e = RuntimeError(
+                            f"Proxy failed to start with exit code {status}"
+                        )
+                        raise e from None
+                await asyncio.sleep(0.5)
+
+        # process_exited can only resolve with a RuntimeError when the process has exited,
+        # otherwise it must be cancelled.
+        process_exited = asyncio.ensure_future(wait_for_process())
+
+        # wait for both servers to be ready (or one server to fail)
+        server_futures = [
+            asyncio.ensure_future(server.wait_up(10))
+            for server in (public_server, api_server)
+        ]
+        servers_ready = asyncio.gather(*server_futures)
+
+        # wait for process to crash or servers to be ready,
+        # whichever comes first
+        wait_timeout = 15
+        ready, pending = await asyncio.wait(
+            [
+                process_exited,
+                servers_ready,
+            ],
+            return_when=asyncio.FIRST_COMPLETED,
+            timeout=wait_timeout,
+        )
+        for task in [servers_ready, process_exited] + server_futures:
+            # cancel any pending tasks
+            if not task.done():
+                task.cancel()
+        if not ready:
+            # timeouts passed to wait_up should prevent this,
+            # but weird things like DNS delays may result in
+            # wait_up taking a lot longer than it should
+            raise TimeoutError(
+                f"Waiting for proxy endpoints didn't complete in {wait_timeout}s"
+            )
+        if process_exited in ready:
+            # process exited, this will raise RuntimeError
+            await process_exited
+        else:
+            # if we got here, servers_ready is done
+            # await it to make sure exceptions are raised
+            await servers_ready
+
         self.log.debug("Proxy started and appears to be up")
         pc = PeriodicCallback(self.check_running, 1e3 * self.check_running_interval)
         self._check_running_callback = pc

jupyterhub/utils.py

@@ -14,6 +14,7 @@
 import ssl
 import sys
 import threading
+import time
 import uuid
 import warnings
 from binascii import b2a_hex
@@ -90,6 +91,8 @@ def can_connect(ip, port):
     except OSError as e:
         if e.errno not in {errno.ECONNREFUSED, errno.ETIMEDOUT}:
             app_log.error("Unexpected error connecting to %s:%i %s", ip, port, e)
+        else:
+            app_log.debug("Server at %s:%i not ready: %s", ip, port, e)
         return False
     else:
         return True
@@ -242,26 +245,31 @@ async def wait_for_server(ip, port, timeout=10):
     """Wait for any server to show up at ip:port."""
     if ip in {'', '0.0.0.0', '::'}:
         ip = '127.0.0.1'
+    app_log.debug("Waiting %ss for server at %s:%s", timeout, ip, port)
+    tic = time.perf_counter()
     await exponential_backoff(
         lambda: can_connect(ip, port),
         "Server at {ip}:{port} didn't respond in {timeout} seconds".format(
             ip=ip, port=port, timeout=timeout
         ),
         timeout=timeout,
     )
+    toc = time.perf_counter()
+    app_log.debug("Server at %s:%s responded in %.2fs", ip, port, toc - tic)
 
 
 async def wait_for_http_server(url, timeout=10, ssl_context=None):
     """Wait for an HTTP Server to respond at url.
 
     Any non-5XX response code will do, even 404.
     """
-    loop = ioloop.IOLoop.current()
-    tic = loop.time()
     client = AsyncHTTPClient()
     if ssl_context:
         client.ssl_options = ssl_context
 
+    app_log.debug("Waiting %ss for server at %s", timeout, url)
+    tic = time.perf_counter()
+
     async def is_reachable():
         try:
             r = await client.fetch(url, follow_redirects=False)
@@ -294,6 +302,8 @@ async def is_reachable():
         ),
         timeout=timeout,
     )
+    toc = time.perf_counter()
+    app_log.debug("Server at %s responded in %.2fs", url, toc - tic)
     return re