Add health check servicer for agent

Dockerfile.agent

@@ -7,7 +7,7 @@ ARG VERSION
 
 RUN apt-get update && apt-get install build-essential -y
 
-RUN pip install prometheus-client
+RUN pip install prometheus-client grpcio-health-checking
 RUN pip install --no-cache-dir -U flytekit==$VERSION \
   flytekitplugins-bigquery==$VERSION \
   flytekitplugins-airflow==$VERSION \

flytekit/clis/sdk_in_container/serve.py

@@ -1,12 +1,13 @@
 from concurrent import futures
 
+import grpc
 import rich_click as click
+from flyteidl.service import agent_pb2
 from flyteidl.service.agent_pb2_grpc import (
     add_AgentMetadataServiceServicer_to_server,
     add_AsyncAgentServiceServicer_to_server,
     add_SyncAgentServiceServicer_to_server,
 )
-from grpc import aio
 
 
 @click.group("serve")
@@ -52,22 +53,46 @@ def agent(_: click.Context, port, worker, timeout):
 
 
 async def _start_grpc_server(port: int, worker: int, timeout: int):
-    click.secho("Starting up the server to expose the prometheus metrics...", fg="blue")
     from flytekit.extend.backend.agent_service import AgentMetadataService, AsyncAgentService, SyncAgentService
 
-    try:
-        from prometheus_client import start_http_server
-
-        start_http_server(9090)
-    except ImportError as e:
-        click.secho(f"Failed to start the prometheus server with error {e}", fg="red")
+    _start_http_server()
     click.secho("Starting the agent service...", fg="blue")
-    server = aio.server(futures.ThreadPoolExecutor(max_workers=worker))
+    server = grpc.aio.server(futures.ThreadPoolExecutor(max_workers=worker))
 
     add_AsyncAgentServiceServicer_to_server(AsyncAgentService(), server)
     add_SyncAgentServiceServicer_to_server(SyncAgentService(), server)
     add_AgentMetadataServiceServicer_to_server(AgentMetadataService(), server)
+    _start_health_check_server(server, worker)
 
     server.add_insecure_port(f"[::]:{port}")
     await server.start()
     await server.wait_for_termination(timeout)
+
+
+def _start_http_server():
+    try:
+        from prometheus_client import start_http_server
+
+        click.secho("Starting up the server to expose the prometheus metrics...", fg="blue")
+        start_http_server(9090)
+    except ImportError as e:
+        click.secho(f"Failed to start the prometheus server with error {e}", fg="red")
+
+
+def _start_health_check_server(server: grpc.Server, worker: int):
+    try:
+        from grpc_health.v1 import health, health_pb2, health_pb2_grpc
+
+        health_servicer = health.HealthServicer(
+            experimental_non_blocking=True,
+            experimental_thread_pool=futures.ThreadPoolExecutor(max_workers=worker),
+        )
+
+        for service in agent_pb2.DESCRIPTOR.services_by_name.values():
+            health_servicer.set(service.full_name, health_pb2.HealthCheckResponse.SERVING)
+        health_servicer.set(health.SERVICE_NAME, health_pb2.HealthCheckResponse.SERVING)
+
+        health_pb2_grpc.add_HealthServicer_to_server(health_servicer, server)
+
+    except ImportError as e:
+        click.secho(f"Failed to start the health check servicer with error {e}", fg="red")