Use 1 playbook for benchmark installation

playbooks/bench-server.yml

-#!/usr/bin/env ansible-playbook
----
-
-- name: DEPLOY BENCHMARK SERVER
-  hosts:
-    - bench_server
-  tags:
-    - bench_server
-  roles:
-    - bench-server
-
-...

playbooks/bench-worker.yml

-#!/usr/bin/env ansible-playbook
----
-
-- name: DEPLOY BENCHMARK WORKERS
-  hosts:
-    - bench_worker
-  tags:
-    - bench_worker
-  roles:
-    - bench-worker
-
-...

playbooks/bench.yml

+#!/usr/bin/env ansible-playbook
+---
+
+- name: DEPLOY BENCHMARK SERVER
+  hosts: bench_server
+  pre_tasks:
+    - name: "Fail is benchmark server is not unique"
+      fail:
+        msg: "Benchmark server must be unique"
+      when: groups['bench_server'] | length > 1
+  tags: bench_server
+  roles: 
+    - bench-server
+
+- name: DEPLOY BENCHMARK WORKERS
+  hosts: bench_worker
+  tags: bench_worker
+  roles: 
+    - bench-worker
+
+...