Add Kestrel keep alive ping section (#20261)

Author: JamesNK

aspnetcore/fundamentals/servers/kestrel.md

@@ -340,6 +340,30 @@ webBuilder.ConfigureKestrel(serverOptions =>
 
 The default value is 96 KB (98,304).
 
+::: moniker range=">= aspnetcore-5.0"
+
+### HTTP/2 keep alive ping configuration
+
+Kestrel can be configured to send HTTP/2 pings to connected clients. HTTP/2 pings serve multiple purposes:
+
+* Keep idle connections alive. Some clients and proxy servers close connections that are idle. HTTP/2 pings are considered as activity on a connection and prevent the connection from being closed as idle.
+* Close unhealthy connections. Connections where the client doesn't respond to the keep alive ping in the configured time are closed by the server.
+
+There are two configuration options related to HTTP/2 keep alive pings:
+
+* `Http2.KeepAlivePingInterval` is a `TimeSpan` that configures the ping internal. The server sends a keep alive ping to the client if it doesn't receive any frames for this period of time. Keep alive pings are disabled when this option is set to `TimeSpan.MaxValue`. The default value is `TimeSpan.MaxValue`.
+* `Http2.KeepAlivePingTimeout` is a `TimeSpan` that configures the ping timeout. If the server doesn't receive any frames, such as a response ping, during this timeout then the connection is closed. Keep alive timeout is disabled when this option is set to `TimeSpan.MaxValue`. The default value is 20 seconds.
+
+```csharp
+webBuilder.ConfigureKestrel(serverOptions =>
+{
+    serverOptions.Limits.Http2.KeepAlivePingInterval = TimeSpan.FromSeconds(30);
+    serverOptions.Limits.Http2.KeepAlivePingTimeout = TimeSpan.FromSeconds(60);
+});
+```
+
+::: moniker-end
+
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