What is the Ray Client?
The Ray Client is an API that connects a python script to a Ray cluster. Effectively, it allows you to leverage a remote Ray cluster just like you would with Ray running on your local machine.
ray.client(...).connect(), you can connect to a remote cluster and scale out your Ray code, while maintaining the ability to develop interactively in a python shell.
# You can run this code outside of the Ray cluster! import ray # Starting the Ray client. This connects to a remote Ray cluster. ray.client("<head_node_host>:10001").connect() # Normal Ray code follows @ray.remote def do_work(x): return x ** x do_work.remote(2) #....
How do you use the Ray client?¶
Step 1: set up your Ray cluster¶
First, you’ll want to create a remote Ray cluster. Follow the directions in Ray Cluster Quick Start to do this.
If using the Ray cluster launcher, the remote cluster will be listening on port
10001 of the head node. If necessary, you can modify this port by setting
--ray-client-server-port to the
ray start command.
If not using the Ray cluster launcher, you can start the “Ray Client Server” manually on the head node of your remote cluster by running the following:
python -m ray.util.client.server [--host host_ip] [--port port] [--redis-address address] [--redis-password password]
Step 2: Check ports¶
Step 3: Run Ray code¶
Now, connect to the Ray Cluster with the following and then use Ray like you normally would:
import ray # replace with the appropriate host and port ray.client("<head_node_host>:10001").connect() # Normal Ray code follows @ray.remote def do_work(x): return x ** x do_work.remote(2) #....
Things to know¶
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.
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.