docs: update on-premise example

docs/getting-started/examples.md

@@ -211,42 +211,36 @@ from diagrams.onprem.database import PostgreSQL
 from diagrams.onprem.inmemory import Redis
 from diagrams.onprem.logging import Fluentd
 from diagrams.onprem.monitoring import Grafana, Prometheus
-from diagrams.onprem.network import Linkerd, Nginx
+from diagrams.onprem.network import Nginx
 from diagrams.onprem.queue import Kafka
-from diagrams.onprem.workflow import Airflow
 
 with Diagram("On-Premise System Architecture", show=False):
     ingress = Nginx("ingress")
 
-    with Cluster("Service Cluster"):
-        svcmesh = Linkerd("svcmesh")
-        grpcsvc = [Server("grpc1"), Server("grpc2"), Server("grpc3")]
-        svcmesh >> grpcsvc
-
-    with Cluster("Database HA"):
-        maindb_master = PostgreSQL("maindb")
-        maindb_replica = PostgreSQL("replica")
-        maindb_master - maindb_replica
-        grpcsvc >> maindb_master
+    metrics = Prometheus("metric")
+    metrics << Grafana("monitoring")
 
-    maindb_replica >> Airflow("scheduler")
+    with Cluster("Service Cluster"):
+        grpcsvc = [
+            Server("grpc1"),
+            Server("grpc2"),
+            Server("grpc3")]
 
     with Cluster("Sessions HA"):
-        session_master = Redis("session")
-        session_master - Redis("replica")
-        grpcsvc >> session_master
-
-    logaggr = Fluentd("aggregator")
-    logaggr >> Kafka("stream") >> Spark("log analytics")
-    grpcsvc >> logaggr
+        master = Redis("session")
+        master - Redis("replica") << metrics
+        grpcsvc >> master
 
-    metricq = Kafka("buffer")
-    metricq >> Prometheus("metric") >> Grafana("monitoring")
+    with Cluster("Database HA"):
+        master = PostgreSQL("users")
+        master - PostgreSQL("slave") << metrics
+        grpcsvc >> master
 
-    logaggr >> metricq
-    svcmesh >> metricq
+    with Cluster("Log Streaming"):
+        aggregator = Fluentd("logging")
+        aggregator >> Kafka("stream") >> Spark("analytics")
 
-    ingress >> svcmesh
+    ingress >> grpcsvc >> aggregator
 ```
 
 ![on-premise system architecture diagram](/img/on-premise_system_architecture.png)