Spark executor driver unknown host issue - apache-spark

Question

Currently I got an issue when using spark. Here is the details.
I setup a spark cluster on VM with three nodes, one is master and the other two are worker.
Spark version is 3.0.0.
I created an application and deployed it into K8S pod.
Then I triggered the application in my K8S pod.
The code I created my Spark Context is like this.
Code:
val conf = SparkConf().setMaster(sparkMaster).setAppName(appName)
.set("spark.cassandra.connection.host", hosts)
.set("spark.cassandra.connection.port", port.toString())
.set("spark.cores.max", sparkCore)
.set("spark.executor.memory", executorMemory)
.set("spark.network.timeout", "50000")
Then I got the error that :
Spark Executor Command:
"/usr/lib/jvm/java-11-openjdk-11.0.7.10-4.el7_8.x86_64/bin/java" "-cp"
"/opt/spark3/conf/:/opt/spark3/jars/*:/etc/hadoop/conf" "-Xmx1024M"
"-Dspark.network.timeout=50000" "-Dspark.driver.port=34471"
"-Dspark.cassandra.connection.port=9042"
"org.apache.spark.executor.CoarseGrainedExecutorBackend"
"--driver-url"
"spark://CoarseGrainedScheduler#my-spark-application-gjwd7:34471"
"--executor-id" "281" "--hostname" "100.84.162.9" "--cores" "1"
"--app-id" "app-20200722115716-0000" "--worker-url"
"spark://Worker#100.84.162.9:33670"
The error is like this:
Exception in thread "main" java.lang.reflect.UndeclaredThrowableException
Caused by: org.apache.spark.SparkException: Exception thrown in awaitResult:
Caused by: java.io.IOException: Failed to connect to my-spark-application-gjwd7:34471
Caused by: java.net.UnknownHostException: my-spark-application-gjwd7
I think this issue is caused by that the worker node can not call back to the driver, since my driver is in the K8S pod.
Do you know how can I resolve this issue. I have some concerns here.
1.How can I set the driver host and port in my code for spark context? port is random according to Spark.
2.How can Spark executor callback to a K8S pod where the driver is running?