Ray Client

Basic usage

The Ray client server is automatically started on port 10001 when you use ray start --head or Ray in an autoscaling cluster. The port can be changed by specifying --ray-client-server-port in the ray start command to be any integer between 1024 and 65535.

To start the server manually, you can run:

python -m ray.util.client.server [--host host_ip] [--port port] [--redis-address address] [--redis-password password]

This runs ray.init() with default options and exposes the client gRPC port at host_ip:port (by default, Providing redis-address and redis-password will be passed into ray.init() when the server starts, allowing connection to an existing Ray cluster, as per the cluster setup instructions.

From here, another Ray script can access that server from a networked machine with ray.util.connect()

import ray
import ray.util

ray.util.connect("<head_node_host>:10001")  # replace with the appropriate host and port

# Normal Ray code follows
def do_work(x):
    return x ** x


When the client disconnects, any object or actor references held by the server on behalf of the client are dropped, as if directly disconnecting from the cluster.

Versioning requirements

Generally, the client Ray version must match the server Ray version. An error will be raised if an incompatible version is used.

Similarly, the minor Python (e.g., 3.6 vs 3.7) must match between the client and server. An error will be raised if this is not the case.