fix: Wait for healthy actor in arcade dev (#142)

Context: Currently, `arcade dev` starts the actor process and then waits
a hardcoded amount of time (2sec) for the actor to start up. This isn't
enough time on some slower machines, which leads to the engine trying to
start but failing.

Fix: Wait until the actor is healthy according to its own
`/actor/health` endpoint.

arcade/arcade/cli/launcher.py

@@ -1,9 +1,11 @@
+import http.client
 import io
 import ipaddress
 import logging
 import os
 import shutil
 import signal
+import socket
 import subprocess
 import sys
 import threading
@@ -28,8 +30,8 @@ if os.environ.get("HOMEBREW_REPOSITORY") is not None:
 
 
 def start_servers(
-    host: str,
-    port: int,
+    actor_host: str,
+    actor_port: int,
     engine_config: str | None,
     engine_env: str | None = None,
     debug: bool = False,
@@ -45,8 +47,8 @@ def start_servers(
         debug: Whether to run in debug mode.
     """
     # Validate host and port
-    host = _validate_host(host)
-    port = _validate_port(port)
+    actor_host = _validate_host(actor_host)
+    actor_port = _validate_port(actor_port)
 
     # Ensure engine_config is provided and validated
     engine_config = _get_config_file(engine_config, default_filename="engine.yaml")
@@ -55,13 +57,13 @@ def start_servers(
     env_file = _get_config_file(engine_env, default_filename="arcade.env", optional=True)
 
     # Prepare command-line arguments for the actor server and engine
-    actor_cmd = _build_actor_command(host, port, debug)
+    actor_cmd = _build_actor_command(actor_host, actor_port, debug)
 
     # even if the user didn't pass an env file we may have found it in the default locations
     engine_cmd = _build_engine_command(engine_config, engine_env=env_file if env_file else None)
 
     # Start and manage the processes
-    _manage_processes(actor_cmd, engine_cmd, debug=debug)
+    _manage_processes(actor_cmd, actor_host, actor_port, engine_cmd, debug=debug)
 
 
 def _validate_host(host: str) -> str:
@@ -239,6 +241,8 @@ def _build_engine_command(engine_config: str | None, engine_env: str | None = No
 
 def _manage_processes(
     actor_cmd: list[str],
+    actor_host: str,
+    actor_port: int,
     engine_cmd: list[str],
     engine_env: dict[str, str] | None = None,
     debug: bool = False,
@@ -273,8 +277,7 @@ def _manage_processes(
             console.print("Starting actor server...", style="bold green")
             actor_process = _start_process("Actor", actor_cmd, debug=debug)
 
-            # Wait a bit to ensure actor is up
-            time.sleep(2)
+            _wait_for_healthy_actor(actor_process, actor_host, actor_port)
 
             # Start the engine
             console.print("Starting engine...", style="bold green")
@@ -356,6 +359,28 @@ def _start_process(
         raise RuntimeError(f"Failed to start {name}")
 
 
+def _wait_for_healthy_actor(
+    actor_process: subprocess.Popen, actor_host: str, actor_port: int
+) -> None:
+    """Wait until an HTTP request to `host:port/actor/health` returns 200"""
+
+    while not actor_process.poll():  # Stop waiting if the actor process has exited
+        time.sleep(1)
+        try:
+            conn = http.client.HTTPConnection(actor_host, actor_port, timeout=1)
+            conn.request("GET", "/actor/health")
+            res = conn.getresponse()
+            if res.status == 200:
+                break
+            conn.close()
+        except (socket.gaierror, http.client.HTTPException, ConnectionRefusedError, TimeoutError):
+            pass  # Handle expected exceptions gracefully
+        console.print("Waiting for actor to start...", style="bold yellow")
+
+    time.sleep(1)  # Wait just a little longer for everything to settle (discovered experimentally)
+    console.print("Actor is healthy", style="bold green")
+
+
 def _stream_output(process: subprocess.Popen, name: str) -> None:
     """
     Streams the output from a subprocess to the console.

arcade/arcade/core/config_model.py

@@ -118,6 +118,14 @@ class Config(BaseConfig):
 
         config_data = yaml.safe_load(config_file_path.read_text())
 
+        if config_data is None:
+            raise ValueError(
+                "Invalid credentials.yaml file. Please ensure it is a valid YAML file."
+            )
+
+        if "cloud" not in config_data:
+            raise ValueError("Invalid credentials.yaml file. Expected a 'cloud' key.")
+
         try:
             return cls(**config_data["cloud"])
         except ValidationError as e: