support set upstream host

docs/07.Reference/7.02.Filters.md

@@ -3,6 +3,7 @@
 
 - [Proxy](#proxy)
   - [Health Check](#health-check)
+  - [Request Host](#request-host)
   - [Configuration](#configuration)
   - [Results](#results)
 - [SimpleHTTPProxy](#simplehttpproxy)
@@ -248,6 +249,38 @@ pools:
         type: contains
 ```
 
+### Request Host
+
+By default, if the client's request host is `example.com` and the pools.servers.url is IP-based, Easegress will forward the request to the backend with the host `example.com`. However, if `pools.servers.url` is a domain, such as `http://demo.com:9090`, Easegress will automatically update the request's host to `demo.com:9090` before sending it to the backend. To prevent this and retain the original client request host, use the `keepHost` option as shown below:
+
+```yaml
+kind: Proxy
+name: proxy-example-3
+pools:
+- servers:
+  - url: http://demo.com:9090
+    keepHost: true
+  loadBalance:
+    policy: roundRobin
+maxRedirection: 10
+```
+
+Conversely, if your `pools.servers.url` is IP-based and you prefer the backend request to use this IP, activate the `setUpstreamHost` option as illustrated below:
+
+```yaml 
+kind: Proxy
+name: proxy-example-4
+pools:
+- setUpstreamHost: true
+  servers:
+  - url: http://demo.com:9090
+  loadBalance:
+    policy: roundRobin
+maxRedirection: 10
+```
+
+Note that `keepHost` takes precedence over `setUpstreamHost` because `keepHost` applies to individual servers, whereas `setUpstreamHost` affects the entire pool.
+
 ### Configuration
 | Name | Type | Description | Required |
 | ---- | ---- | ----------- | -------- |
@@ -1746,6 +1779,7 @@ Rules to revise request header.
 | circuitBreakerPolicy | string | CircuitBreaker policy name | No |
 | failureCodes | []int | Proxy return result of failureCode when backend resposne's status code in failureCodes. The default value is 5xx | No |
 | healthCheck | ProxyHealthCheckSpec | Health check. Full example with details in [Proxy Health Check](#health-check) | No |
+| setUpstreamHost | bool | Set request host to the host of backend server url if true. Default is false. | No |
 
 
 ### proxy.Server

pkg/filters/proxies/httpproxy/pool.go

@@ -135,7 +135,7 @@ func removeHopByHopHeaders(h http.Header) {
 	*/
 }
 
-func (spCtx *serverPoolContext) prepareRequest(svr *Server, ctx stdcontext.Context, mirror bool) error {
+func (spCtx *serverPoolContext) prepareRequest(pool *ServerPool, svr *Server, ctx stdcontext.Context, mirror bool) error {
 	req := spCtx.req
 
 	u := req.Std().URL
@@ -154,6 +154,7 @@ func (spCtx *serverPoolContext) prepareRequest(svr *Server, ctx stdcontext.Conte
 	if err != nil {
 		return err
 	}
+	svrHost := stdr.Host
 
 	stdr.Header = req.HTTPHeader().Clone()
 	removeHopByHopHeaders(stdr.Header)
@@ -164,6 +165,13 @@ func (spCtx *serverPoolContext) prepareRequest(svr *Server, ctx stdcontext.Conte
 		stdr.Host = req.Host()
 	}
 
+	// set upstream host if server is explicitly told to set the host of the request.
+	// KeepHost has higher priority than SetUpstreamHost.
+	if pool.spec.SetUpstreamHost && !svr.KeepHost {
+		stdr.Host = svrHost
+		stdr.Header.Add("Host", svrHost)
+	}
+
 	if spCtx.span != nil {
 		spCtx.span.InjectHTTP(stdr)
 	}
@@ -352,7 +360,7 @@ func (sp *ServerPool) handleMirror(spCtx *serverPoolContext) {
 		return
 	}
 
-	err := spCtx.prepareRequest(svr, spCtx.req.Context(), true)
+	err := spCtx.prepareRequest(sp, svr, spCtx.req.Context(), true)
 	if err != nil {
 		logger.Errorf("%s: failed to prepare request: %v", sp.Name, err)
 		return
@@ -463,7 +471,7 @@ func (sp *ServerPool) doHandle(stdctx stdcontext.Context, spCtx *serverPoolConte
 	// prepare the request to send.
 	statResult := &gohttpstat.Result{}
 	stdctx = gohttpstat.WithHTTPStat(stdctx, statResult)
-	if err := spCtx.prepareRequest(svr, stdctx, false); err != nil {
+	if err := spCtx.prepareRequest(sp, svr, stdctx, false); err != nil {
 		logger.Errorf("%s: failed to prepare request: %v", sp.Name, err)
 		return serverPoolError{http.StatusInternalServerError, resultInternalError}
 	}

pkg/filters/proxies/serverpool.go

@@ -47,6 +47,7 @@ type ServerPoolBase struct {
 type ServerPoolBaseSpec struct {
 	ServerTags      []string         `json:"serverTags,omitempty" jsonschema:"uniqueItems=true"`
 	Servers         []*Server        `json:"servers,omitempty"`
+	SetUpstreamHost bool             `json:"setUpstreamHost,omitempty"`
 	ServiceRegistry string           `json:"serviceRegistry,omitempty"`
 	ServiceName     string           `json:"serviceName,omitempty"`
 	LoadBalance     *LoadBalanceSpec `json:"loadBalance,omitempty"`