fix: spark-k8s graceful shutdown on SIGTERM

Author: Maleware

spark-k8s/Dockerfile.3

@@ -258,4 +258,4 @@ EOF
 USER ${STACKABLE_USER_UID}
 
 WORKDIR ${SPARK_HOME}
-ENTRYPOINT [ "/stackable/run-spark.sh" ]
+ENTRYPOINT [ "/usr/bin/tini", "-s", "--", "/stackable/run-spark.sh" ]

spark-k8s/Dockerfile.4

@@ -230,4 +230,4 @@ EOF
 USER ${STACKABLE_USER_UID}
 
 WORKDIR ${SPARK_HOME}
-ENTRYPOINT [ "/stackable/run-spark.sh" ]
+ENTRYPOINT [ "/usr/bin/tini", "-s", "--", "/stackable/run-spark.sh" ]

spark-k8s/stackable/run-spark.sh

@@ -1,10 +1,23 @@
 #!/bin/bash
 
-eval "$_STACKABLE_PRE_HOOK"
+  eval "$_STACKABLE_PRE_HOOK"
 
-/stackable/spark/kubernetes/dockerfiles/spark/entrypoint.sh "$@"
-result=$?
+  # Forward SIGTERM to the Spark entrypoint to support spark JVM's gracefully shutdown.
+  /stackable/spark/kubernetes/dockerfiles/spark/entrypoint.sh "$@" &
+  child_pid=$!
 
-eval "$_STACKABLE_POST_HOOK"
+  _handle_term() {
+    kill -TERM "$child_pid" 2>/dev/null || true
+  }
+  trap _handle_term TERM INT
 
-exit $result
+  # `wait` returns immediately when the trap fires; loop until the child is actually gone.
+  wait "$child_pid"
+  while kill -0 "$child_pid" 2>/dev/null; do
+    wait "$child_pid" 2>/dev/null || true
+  done
+  result=$?
+
+  eval "$_STACKABLE_POST_HOOK"
+
+  exit $result