Promote keda and flight-sql to optional features (#1079)

* remove flight-sql from scheduler default options

* keda-scheduler is optional feature (off by default)

ballista/scheduler/Cargo.toml

@@ -34,8 +34,9 @@ name = "ballista-scheduler"
 path = "src/bin/main.rs"
 
 [features]
-default = ["flight-sql"]
+default = []
 flight-sql = []
+keda-scaler = []
 prometheus-metrics = ["prometheus", "once_cell"]
 
 [dependencies]

ballista/scheduler/src/scheduler_process.rs

@@ -29,8 +29,10 @@ use std::{net::SocketAddr, sync::Arc};
 use crate::api::get_routes;
 use crate::cluster::BallistaCluster;
 use crate::config::SchedulerConfig;
+#[cfg(feature = "flight-sql")]
 use crate::flight_sql::FlightSqlServiceImpl;
 use crate::metrics::default_metrics_collector;
+#[cfg(feature = "keda-scaler")]
 use crate::scheduler_server::externalscaler::external_scaler_server::ExternalScalerServer;
 use crate::scheduler_server::SchedulerServer;
 
@@ -67,11 +69,11 @@ pub async fn start_server(
         .max_encoding_message_size(config.grpc_server_max_encoding_message_size as usize)
         .max_decoding_message_size(config.grpc_server_max_decoding_message_size as usize);
 
-    let keda_scaler = ExternalScalerServer::new(scheduler_server.clone());
+    let tonic_builder = create_grpc_server().add_service(scheduler_grpc_server);
 
-    let tonic_builder = create_grpc_server()
-        .add_service(scheduler_grpc_server)
-        .add_service(keda_scaler);
+    #[cfg(feature = "keda-scaler")]
+    let tonic_builder =
+        tonic_builder.add_service(ExternalScalerServer::new(scheduler_server.clone()));
 
     #[cfg(feature = "flight-sql")]
     let tonic_builder = tonic_builder.add_service(FlightServiceServer::new(

ballista/scheduler/src/scheduler_server/mod.rs

@@ -44,12 +44,14 @@ use crate::state::task_manager::TaskLauncher;
 use crate::state::SchedulerState;
 
 // include the generated protobuf source as a submodule
+#[cfg(feature = "keda-scaler")]
 #[allow(clippy::all)]
 pub mod externalscaler {
     include!(concat!(env!("OUT_DIR"), "/externalscaler.rs"));
 }
 
 pub mod event;
+#[cfg(feature = "keda-scaler")]
 mod external_scaler;
 mod grpc;
 pub(crate) mod query_stage_scheduler;