restart-server: Send client reload events in the background.

For deploys with --skip-puppet, this makes the output visible much
more promptly.

scripts/lib/upgrade-zulip-stage-3

@@ -367,7 +367,7 @@ else:
     subprocess.check_call(["./scripts/lib/run_hooks.py", "post-deploy", *hooks_args])
 
     if not args.skip_client_reloads and not args.only_django:
-        subprocess.check_call(["./scripts/reload-clients"], preexec_fn=su_to_zulip)
+        subprocess.check_call(["./scripts/reload-clients", "--background"], preexec_fn=su_to_zulip)
 
 if args.audit_fts_indexes:
     logging.info("Correcting full-text search indexes for updated dictionary files")

scripts/reload-clients

@@ -31,6 +31,7 @@ parser = argparse.ArgumentParser()
 parser.add_argument(
     "--rate", type=int, help="Number of clients to reload per second", default=reload_rate
 )
+parser.add_argument("--background", action="store_true", help="Daemonize the process")
 
 args = parser.parse_args()
 reload_rate = args.rate
@@ -49,8 +50,24 @@ retry = Retry(total=3, backoff_factor=1, allowed_methods=Retry.DEFAULT_ALLOWED_M
 c = requests.Session()
 c.mount("http://", HTTPAdapter(max_retries=retry))
 
+log_filename = None
+if args.background:
+    # Double-fork to daemonize
+    pid = os.fork()
+    if pid > 0:
+        sys.exit(0)
+    os.setsid()
+    pid = os.fork()
+    if pid > 0:
+        sys.exit(0)
+    log_filename = "/var/log/zulip/reload-clients.log"
+
 logging.Formatter.converter = time.gmtime
-logging.basicConfig(format="%(asctime)s reload-clients: %(message)s", level=logging.INFO)
+logging.basicConfig(
+    format="%(asctime)s reload-clients: %(message)s",
+    level=logging.INFO,
+    filename=log_filename,
+)
 
 first = True
 server_total = 0

scripts/restart-server

@@ -245,7 +245,8 @@ if (action == "start" or args.less_graceful) and not args.only_django:
 if has_application_server() and not args.skip_client_reloads and not args.only_django:
     # All of the servers have been (re)started; now enqueue events in
     # the Tornado servers to tell clients to reload.
-    subprocess.check_call(["./scripts/reload-clients"])
+    logging.info("Sending reload events to clients in the background")
+    subprocess.check_call(["./scripts/reload-clients", "--background"])
 
 logging.info("Done!")
 print(OKGREEN + f"Zulip {action}ed successfully!" + ENDC)