guides/features: add document for how to gracefully shutdown server (grpc#1388)

Author: purnesh42H

content/en/docs/guides/server-graceful-stop.md

@@ -0,0 +1,87 @@
+---
+title: Graceful Shutdown
+description: >-
+  Explains how to gracefully shut down a gRPC server to avoid causing RPC
+  failures for connected clients.
+---
+
+### Overview
+
+gRPC servers often need to shut down gracefully, ensuring that in-flight RPCs
+are completed within a reasonable time frame and new RPCs are no longer
+accepted. The "Graceful shutdown function" facilitates this process, allowing
+the server to transition smoothly without abruptly terminating active
+connections.
+
+When the "Graceful shutdown function" is called, the server immediately
+notifies all clients to stop sending new RPCs. Then after the clients have
+received that notification, the server will stop accepting new RPCs. In-flight
+RPCs are allowed to continue until they complete or a specified deadline is
+reached. Once all active RPCs finish or the deadline expires, the server shuts
+down completely.
+
+Because graceful shutdown helps prevent clients from encountering RPC failures,
+it should be used if possible.  However, gRPC also provides a forceful shutdown
+mechanism which will immediately cause the server to stop serving and close all
+connections, which results in the failure of any in-flight RPCs.
+
+### How to do Graceful Server Shutdown
+
+The exact implementation of the "Graceful shutdown function" varies depending on
+the programming language you are using. However, the general pattern
+involves:
+
+- Initiating the graceful shutdown process by calling the "Graceful shutdown
+  function" on your gRPC server object. This function blocks until all
+  currently running RPCs complete. This ensures that in-flight requests are
+  allowed to finish processing.
+- Specify a timeout period to limit the time allowed for in-progress RPCs to
+  finish. It's crucial to separately call the "Forceful shutdown function" on
+  the server object using a timer mechanism (depending on your language) to
+  trigger a forceful shutdown after a predefined duration. This
+  acts as a safety net, ensuring that the server eventually shuts down even if
+  some in-flight RPCs don't complete within a reasonable time frame. This
+  prevents indefinite blocking.
+
+The following shows the sequence of events that occur during the graceful
+shutdown process. When a server's graceful shutdown is invoked, in-flight RPCs
+continue to process, but new RPCs are rejected. If some in-flight RPCs are not
+finished in time, the server is forcefully shut down.
+```mermaid
+sequenceDiagram
+Client->>Server: New RPC Request 1
+Client->>Server: New RPC Request 2
+Server-->>Server: Graceful Shutdown Invoked
+Server->>Client: Continues Processing In-Flight RPCs
+Client->>Client: Detects server shutdown and finds other servers if available
+alt RPCs complete within timeout
+    Server->>Client: Completes RPC 1
+    Server->>Client: Completes RPC 2
+    Server-->>Server: Graceful Shutdown Complete
+else Timeout reached
+    Server->>Client: Forceful Shutdown Invoked, terminating pending RPCs
+    Server-->>Server: Forceful Shutdown Complete
+end
+```
+The following is a state based view
+```mermaid
+stateDiagram-v2
+    [*] --> SERVING : Server Started
+    SERVING --> GRACEFUL_SHUTDOWN : Graceful Shutdown Called (with Timeout)
+    GRACEFUL_SHUTDOWN --> TERMINATED : In-Flight RPCs Completed (Before Timeout)
+    GRACEFUL_SHUTDOWN --> TIMER_EXPIRED : Timeout Reached
+    TIMER_EXPIRED --> TERMINATED : Forceful Shutdown Called
+```
+
+### Language Support
+
+| Language | Example          |
+|----------|------------------|
+| C++      |                  |
+| Go       | [Go Example]     |
+| Java     | [Java Example]   |
+| Python   |                  |
+
+
+[Go example]: https://github.com/grpc/grpc-go/tree/master/examples/features/gracefulstop
+[Java example]: https://github.com/grpc/grpc-java/tree/master/examples/example-hostname/src/main/java/io/grpc/examples/hostname