To connect an existing Spark application to a Spark Connect server without code modification, the connection must be configured externally. The two primary methods are using a command-line flag when launching the application (like the PySpark shell) or setting an environment variable. The --remote "sc://localhost" flag instructs the PySpark shell to operate in Connect mode and connect to the specified server. Similarly, setting the SPARKREMOTE="sc://localhost" environment variable before launching any Spark application (including a shell or a submitted job) will configure the default SparkSession to connect to the specified remote server, overriding the default behavior of creating a local Spark session.

A. The https:// protocol is incorrect for Spark Connect; the correct protocol is sc://.

D. This option requires modifying the application's source code by adding .remote() to the SparkSession.builder call, which the question explicitly prohibits.

E. spark.connect.grpc.binding.port is a server-side configuration property that specifies the port the Spark Connect server listens on, not how a client connects to it.

1. Apache Spark 3.5.1 Documentation

Spark Connect Overview

"Start Spark Connect server and client": This section explicitly demonstrates the two valid methods.

For the command-line option: "To use Spark Connect with the PySpark shell

run the following command in the Spark root directory: ./bin/pyspark --remote sc://localhost". This validates option B.

For the environment variable: "Alternatively

you can set the SPARKREMOTE environment variable

for example

export SPARKREMOTE="sc://localhost"". This validates option C.

The documentation also shows the code-based method

.remote("sc://localhost")

confirming why option D is a valid method in general but incorrect for this specific question's constraint.