rptest: use 10 nodes in OMB validation tests

Drop the assumed number of nodes from 12 to 10 in OMB validation
tests as that's the default number of nodes in duck.py and also the
number we want to standardize on for all HTT tests.

Author: travisdowns

tests/rptest/redpanda_cloud_tests/omb_validation_test.py

@@ -35,6 +35,11 @@
 
 class OMBValidationTest(RedpandaTest):
 
+    # The numbers of nodes we expect to run with - this value (10) is the default
+    # for duck.py so these tests should just work with that default, but not necessarily
+    # any less than that.
+    CLUSTER_NODES = 10
+
     # common workload details shared among most/all test methods
     WORKLOAD_DEFAULTS = {
         "topics": 1,
@@ -141,7 +146,7 @@ def _consumer_count(self, egress_rate) -> int:
     def _mb_to_mib(self, mb):
         return math.floor(0.9537 * mb)
 
-    @cluster(num_nodes=12)
+    @cluster(num_nodes=CLUSTER_NODES)
     def test_max_connections(self):
         tier_limits = self.tier_limits
 
@@ -150,7 +155,7 @@ def test_max_connections(self):
 
         PRODUCER_TIMEOUT_MS = 5000
         OMB_WORKERS = 4
-        SWARM_WORKERS = 7
+        SWARM_WORKERS = 5
 
         # OMB parameters
         #
@@ -285,7 +290,7 @@ def test_max_connections(self):
         finally:
             self.rpk.delete_topic(swarm_topic_name)
 
-    @cluster(num_nodes=12)
+    @cluster(num_nodes=CLUSTER_NODES)
     def test_max_partitions(self):
         tier_limits = self.tier_limits
 
@@ -320,14 +325,14 @@ def test_max_partitions(self):
             self.redpanda,
             "ACK_ALL_GROUP_LINGER_1MS_IDEM_MAX_IN_FLIGHT",
             (workload, validator),
-            num_workers=10,
+            num_workers=self.CLUSTER_NODES - 1,
             topology="ensemble")
         benchmark.start()
         benchmark_time_min = benchmark.benchmark_time() + 5
         benchmark.wait(timeout_sec=benchmark_time_min * 60)
         benchmark.check_succeed()
 
-    @cluster(num_nodes=12)
+    @cluster(num_nodes=CLUSTER_NODES)
     def test_common_workload(self):
         tier_limits = self.tier_limits
 
@@ -373,14 +378,14 @@ def test_common_workload(self):
         benchmark = OpenMessagingBenchmark(self._ctx,
                                            self.redpanda,
                                            driver, (workload, validator),
-                                           num_workers=10,
+                                           num_workers=self.CLUSTER_NODES - 1,
                                            topology="ensemble")
         benchmark.start()
         benchmark_time_min = benchmark.benchmark_time() + 5
         benchmark.wait(timeout_sec=benchmark_time_min * 60)
         benchmark.check_succeed()
 
-    @cluster(num_nodes=12)
+    @cluster(num_nodes=CLUSTER_NODES)
     def test_retention(self):
         tier_limits = self.tier_limits
 
@@ -439,7 +444,7 @@ def test_retention(self):
         benchmark = OpenMessagingBenchmark(self._ctx,
                                            self.redpanda,
                                            driver, (workload, validator),
-                                           num_workers=10,
+                                           num_workers=self.CLUSTER_NODES - 1,
                                            topology="ensemble")
         benchmark.start()
         benchmark_time_min = benchmark.benchmark_time() + 5