doc: upload file GLS Feature Usage

content/en/docs/kitex/Tutorials/advanced-feature/GLS.md

@@ -0,0 +1,54 @@
+---
+title: "GLS Feature Usage"
+date: 2023-11-29
+weight: 1
+keywords: ["GLS Feature Usage"]
+description: ""
+---
+
+## Server side enable request context backup
+
+- Option on
+  - Use the server option `WithContextBackup`;
+  - The first parameter `enable` indicates that the GLS is enabled;
+  - The second option, `async`, means to enable asynchronous implicitly pass-through (indicating that the context in the asynchronous call to go func () is also transparent fallback)
+
+```go
+svr := xxx.NewServer(new(XXXImpl), server.WithContextBackup(true, true))
+
+```
+
+- Adjust localsession [management options](https://github.com/cloudwego/localsession/blob/main/manager.go#L24) by environment variables
+  - First, enable `WithContextBackup` on the Server side.
+  - Configure `CLOUDWEGO_SESSION_CONFIG_KEY ``= [{Whether to enable asynchronous pass-through}] [, {Global sharding number}] [, {GC interval}] in environment variables `, all three options are optional, **null means use default value**
+    - Ex: `true,10,1h ` means, turn on asynchronous + sharding 10 buckets + 1 hour GC interval
+
+## Client start request context fallback
+
+- Option on
+  - Use the client option `WithContextBackup`;
+  - The parameter handler represents the backup logic BackupHandler customized by the business.
+
+```go
+func(prev, cur context.Context) (ctx context.Context, backup bool)
+
+```
+
+- `Prev` parameter represents the context of the backup
+- `Cur` parameter represents the context obtained by the current client
+- `Ctx` return value represents the final context where the user completes processing
+- `Backup` return value indicates whether to continue localsession [built-in fallback backup ](https://github.com/cloudwego/localsession/blob/main/backup/metainfo.go#L54),  mainly metainfo Persistent KVS pass-through at present
+
+```go
+var expectedKey interface{}
+cli := xxx.NewClient(serverName, client.WithContextBackup(func(prev, cur context.Context) (ctx context.Context, backup bool) {
+    if v := cur.Value(expectedKey); v != nil {
+    // expectedKey exists, no need for recover context
+        return cur, false
+    }
+    // expectedKey doesn't exists, need recover context from prev
+    ctx = context.WithValue(cur, expectedKey, prev.Value(expectedKey))
+    return ctx, true
+})
+
+```