Distributed Ruby, commonly known as DRb, allows Ruby programs to communicate with each other on different machines over a network. This powerful feature enables the implementation of distributed applications, where tasks can be divided and managed across various networked resources. DRb achieves this by allowing objects in one Ruby process to invoke methods on objects in another Ruby process, possibly on a different machine.

Understanding DRb Method Access

At the heart of DRb's functionality is the ability to remotely call methods on objects that exist on different servers or processes. The technology uses Ruby's built-in serialization to marshal and unmarshal objects and method arguments as they cross the network. Here’s how DRb method access typically works:

1. Server Side Setup: A Ruby object is designated as a DRb service by starting a DRb server and specifying the object to be shared and the URI (Uniform Resource Identifier) it should listen on.
2. Client Side Usage: On the client side, the remote object is accessed by connecting to the server’s URI. The client can then call methods on the server object as if it were local.

Implementing Basic DRb Communication

Here's a simple example to show how DRb can be used to access methods across distributed systems:

Server Code:

1require 'drb/drb'
2
3# The URI for the DRb server
4URI="druby://localhost:8787"
5
6# A simple class with a method to be accessed remotely
7class HelloWorld
8  def say_hello
9    "Hello from the server!"
10  end
11end
12
13# Start the DRb server with an instance of HelloWorld
14DRb.start_service(URI, HelloWorld.new)
15puts "Server running at #{URI}"
16
17# Keep the server running
18DRb.thread.join

Client Code:

1require 'drb/drb'
2
3# The URI of the DRb server
4SERVER_URI="druby://localhost:8787"
5
6# Connect to the server
7DRb.start_service
8remote_obj = DRbObject.new_with_uri(SERVER_URI)
9
10# Call the remote method
11puts remote_obj.say_hello  # Outputs: Hello from the server!

Security in DRb

One important aspect of using DRb is ensuring that communication between the client and the server is secure. By default, DRb does not provide mechanisms like authentication or encryption, which means data sent over the network can be intercepted and altered. It is essential to secure DRb connections, especially when dealing with sensitive information. Techniques for securing DRb include:

• Setting up an SSH tunnel for DRb communications.
• Using SSL for DRb connections with tools like drbssl.

Performance Considerations

DRb can become a bottleneck in network communication if not carefully managed. The performance issues primarily arise from:

• Network latency: Method calls that depend on remote execution can significantly slow down if the network is slow.
• Marshalling and unmarshalling data: Complex objects can take considerable time to serialize and deserialize.

Summary

Here is a table summarizing key aspects of DRb method access:

Conclusion

DRb provides a robust way for Ruby objects to interact over a network, enabling distributed application development. While it offers considerable flexibility and power, developers must handle security and performance implications carefully to build efficient and secure applications.