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The process of establishing a connection to AWS Elasticache cluster nodes through a bastion with the help of Python and redis-py-cluster involves the following steps:

1. Configure the bastion host: Set up a bastion host that allows incoming connections from your IP address only. The bastion host should have permissions to connect to the Elasticache cluster.

2. Install redis-py-cluster: Install the redis-py-cluster client library using pip. This library allows you to connect to a Redis cluster and perform operations on it.

3. Configure the client: Create a RedisCluster object and configure it with the proper endpoint URL, port, and other parameters like the cluster node's username and password.

4. Configure the SSH tunnel: Using the SSHTunnelForwarder class from the sshtunnel package, create an SSH tunnel from the bastion host to the Elasticache cluster. The SSH tunnel allows you to securely connect to the Elasticache cluster through the bastion host.

5. Connect to the cluster: Once the SSH tunnel is established, connect to the Redis cluster using the RedisCluster object. You can perform various Redis operations like set(), get(), and delete() on it.

6. Close the SSH tunnel: Once you have finished using the Redis cluster, close the SSH tunnel by calling its close() method.

Example code:

from rediscluster import RedisCluster
from sshtunnel import SSHTunnelForwarder
import redis

ssh_host = 'bastion-host-address'
ssh_username = 'username'
ssh_password = 'password'

redis_host = 'elasticache-address'
redis_port = 6379

# Create an SSH tunnel to the Elasticache cluster through the bastion host
with SSHTunnelForwarder(
    (ssh_host, 22),
    ssh_username=ssh_username,
    ssh_password=ssh_password,
    remote_bind_address=(redis_host, redis_port),
) as tunnel:

    # Configure the Redis object with the endpoint URL and port of the Elasticache cluster nodes
    rc = RedisCluster(
        startup_nodes=[{'host': redis_host, 'port': redis_port}],
        decode_responses=True,
    )

    # Perform a Redis operation
    rc.set('my-key', 'my-value')

    # Close the Redis object
    rc.close()

# Close the SSH tunnel
tunnel.close()