[Serve] Add a minimal cli (#5854)

* Add a minimal cli

* Integrate serve_cli with ray scripts

python/ray/experimental/serve/scripts.py

@@ -0,0 +1,50 @@
+import json
+
+import click
+
+import ray
+import ray.experimental.serve as serve
+
+
+@click.group("serve", help="Commands working with ray serve")
+def serve_cli():
+    pass
+
+
+@serve_cli.command(help="Initialize ray serve components")
+def init():
+    ray.init(address="auto")
+    serve.init(blocking=True)
+
+
+@serve_cli.command(help="Split traffic for a endpoint")
+@click.argument("endpoint", required=True, type=str)
+# TODO(simon): Make traffic dictionary more ergonomic. e.g.
+#     --traffic backend1=0.5 --traffic backend2=0.5
+@click.option(
+    "--traffic",
+    required=True,
+    type=str,
+    help="Traffic dictionary in JSON format")
+def split(endpoint, traffic):
+    ray.init(address="auto")
+    serve.init()
+
+    serve.split(endpoint, json.loads(traffic))
+
+
+@serve_cli.command(help="Scale the number of replicas for a backend")
+@click.argument("backend", required=True, type=str)
+@click.option(
+    "--num-replicas",
+    required=True,
+    type=int,
+    help="New number of replicas to set")
+def scale(backend_tag, num_replicas):
+    if num_replicas <= 0:
+        click.Abort(
+            "Cannot set number of replicas to be smaller or equal to 0.")
+    ray.init(address="auto")
+    serve.init()
+
+    serve.scale(backend_tag, num_replicas)

python/ray/scripts/scripts.py

@@ -827,6 +827,13 @@ cli.add_command(timeline)
 cli.add_command(project_cli)
 cli.add_command(session_cli)
 
+try:
+    from ray.experimental.serve.scripts import serve_cli
+    cli.add_command(serve_cli)
+except Exception as e:
+    logger.debug(
+        "Integrating ray serve command line tool failed with {}".format(e))
+
 
 def main():
     return cli()