Locustfile distribution from master to worker

docs/running-distributed.rst

@@ -38,16 +38,19 @@ Start locust in master mode on one machine::
 
     locust -f my_locustfile.py --master
 
-And then on each worker machine (make sure they also have a copy of the locustfile):
+And then on each worker machine:
 
 .. code-block:: bash
 
-    locust -f my_locustfile.py --worker --master-host <your master's address> --processes 4
+    locust -f - --worker --master-host <your master's address> --processes 4
+
+.. note::
+    The ``-f -`` argument tells Locust to get the locustfile from master instead of from its local filesystem. This feature was introduced in Locust 2.23.0.
 
 Multiple machines, using locust-swarm
 =====================================
 
-Both worker and master need access to the locustfile, and when you make changes to it you'll need to restart all Locust processes. `locust-swarm <https://github.com/SvenskaSpel/locust-swarm>`_ automates this for you. It also solves the issue of firewall/network access from workers to master using SSH tunnels (this is often a problem if the master is running on your workstation and workers are running in some datacenter).
+When you make changes to the locustfile you'll need to restart all Locust processes. `locust-swarm <https://github.com/SvenskaSpel/locust-swarm>`_ automates this for you. It also solves the issue of firewall/network access from workers to master using SSH tunnels (this is often a problem if the master is running on your workstation and workers are running in some datacenter).
 
 .. code-block:: bash
 

locust/argument_parser.py

@@ -1,14 +1,20 @@
 from __future__ import annotations
 
 import locust
+from locust import runners
+from locust.rpc import Message, zmqrpc
 
 import os
 import platform
+import socket
 import sys
 import textwrap
 from typing import Any, NamedTuple
+from uuid import uuid4
 
 import configargparse
+import gevent
+from gevent.event import Event
 
 version = locust.__version__
 
@@ -179,6 +185,46 @@ def get_empty_argument_parser(add_help=True, default_config_files=DEFAULT_CONFIG
     return parser
 
 
+def download_locustfile_from_master(master_host: str, master_port: int) -> str:
+    client_id = socket.gethostname() + "_download_locustfile_" + uuid4().hex
+    tempclient = zmqrpc.Client(master_host, master_port, client_id)
+    got_reply = False
+
+    def ask_for_locustfile():
+        while not got_reply:
+            tempclient.send(Message("locustfile", None, client_id))
+            gevent.sleep(1)
+
+    def wait_for_reply():
+        return tempclient.recv()
+
+    gevent.spawn(ask_for_locustfile)
+    try:
+        # wait same time as for client_ready ack. not that it is really relevant...
+        msg = gevent.spawn(wait_for_reply).get(timeout=runners.CONNECT_TIMEOUT * runners.CONNECT_RETRY_COUNT)
+        got_reply = True
+    except gevent.Timeout:
+        sys.stderr.write(
+            f"Got no locustfile response from master, gave up after {runners.CONNECT_TIMEOUT * runners.CONNECT_RETRY_COUNT}s\n"
+        )
+        sys.exit(1)
+
+    if msg.type != "locustfile":
+        sys.stderr.write(f"Got wrong message type from master {msg.type}\n")
+        sys.exit(1)
+
+    if "error" in msg.data:
+        sys.stderr.write(f"Got error from master: {msg.data['error']}\n")
+        sys.exit(1)
+
+    filename = msg.data["filename"]
+    with open(filename, "w") as local_file:
+        local_file.write(msg.data["contents"])
+
+    tempclient.close()
+    return filename
+
+
 def parse_locustfile_option(args=None) -> list[str]:
     """
     Construct a command line parser that is only used to parse the -f argument so that we can
@@ -201,9 +247,41 @@ def parse_locustfile_option(args=None) -> list[str]:
         action="store_true",
         default=False,
     )
+    # the following arguments are only used for downloading the locustfile from master
+    parser.add_argument(
+        "--worker",
+        action="store_true",
+        env_var="LOCUST_MODE_WORKER",
+    )
+    parser.add_argument(
+        "--master",  # this is just here to prevent argparse from giving the dreaded "ambiguous option: --master could match --master-host, --master-port"
+        action="store_true",
+        env_var="LOCUST_MODE_MASTER",
+    )
+    parser.add_argument(
+        "--master-host",
+        default="127.0.0.1",
+        env_var="LOCUST_MASTER_NODE_HOST",
+    )
+    parser.add_argument(
+        "--master-port",
+        type=int,
+        default=5557,
+        env_var="LOCUST_MASTER_NODE_PORT",
+    )
 
     options, _ = parser.parse_known_args(args=args)
 
+    if options.locustfile == "-":
+        if not options.worker:
+            sys.stderr.write(
+                "locustfile was set to '-' (meaning to download from master) but --worker was not specified.\n"
+            )
+            sys.exit(1)
+        # having this in argument_parser module is a bit weird, but it needs to be done early
+        filename = download_locustfile_from_master(options.master_host, options.master_port)
+        return [filename]
+
     # Comma separated string to list
     locustfile_as_list = [locustfile.strip() for locustfile in options.locustfile.split(",")]
 
@@ -467,7 +545,7 @@ def setup_parser_arguments(parser):
     worker_group.add_argument(
         "--worker",
         action="store_true",
-        help="Set locust to run in distributed mode with this process as worker",
+        help="Set locust to run in distributed mode with this process as worker. Can be combined with setting --locustfile to '-' to download it from master.",
         env_var="LOCUST_MODE_WORKER",
     )
     worker_group.add_argument(

locust/runners.py

@@ -1033,6 +1033,40 @@ def client_listener(self) -> NoReturn:
                 # emit a warning if the worker's clock seem to be out of sync with our clock
                 # if abs(time() - msg.data["time"]) > 5.0:
                 #    warnings.warn("The worker node's clock seem to be out of sync. For the statistics to be correct the different locust servers need to have synchronized clocks.")
+            elif msg.type == "locustfile":
+                logging.debug("Worker requested locust file")
+                assert self.environment.parsed_options
+                filename = (
+                    "locustfile.py"
+                    if self.environment.parsed_options.locustfile == "locustfile"
+                    else self.environment.parsed_options.locustfile
+                )
+                try:
+                    with open(filename) as f:
+                        file_contents = f.read()
+                except Exception as e:
+                    logger.error(
+                        f"--locustfile must be a plain filename (not a module name) for file distribution to work {e}"
+                    )
+                    self.send_message(
+                        "locustfile",
+                        client_id=client_id,
+                        data={
+                            "error": f"locustfile parameter on master must be a plain filename (not a module name) (was '{filename}')"
+                        },
+                    )
+                else:
+                    if getattr(self, "_old_file_contents", file_contents) != file_contents:
+                        logger.warning(
+                            "Locustfile contents changed on disk after first worker requested locustfile, sending new content. If you make any major changes (like changing User class names) you need to restart master."
+                        )
+                    self._old_file_contents = file_contents
+                    self.send_message(
+                        "locustfile",
+                        client_id=client_id,
+                        data={"filename": filename, "contents": file_contents},
+                    )
+                continue
             elif msg.type == "client_stopped":
                 if msg.node_id not in self.clients:
                     logger.warning(f"Received {msg.type} message from an unknown worker: {msg.node_id}.")