nghttpx: SNI based backend server selection

src/shrpx.cc

@@ -1665,14 +1665,16 @@ Connections:
               which  only  lacks  trailing  '/'  (e.g.,  path  "/foo/"
               matches request path  "/foo").  If it does  not end with
               "/", it  performs exact match against  the request path.
-              If host  is given, it  performs exact match  against the
+              If  host  is given,  it  performs  a match  against  the
-              request host.  If  host alone is given,  "/" is appended
+              request host.   For a  request received on  the frontend
-              to it,  so that it  matches all request paths  under the
+              lister  with "sni-fwd"  parameter enabled,  SNI host  is
-              host   (e.g.,   specifying   "nghttp2.org"   equals   to
+              used instead of a request host.  If host alone is given,
-              "nghttp2.org/").  CONNECT  method is  treated specially.
+              "/" is  appended to it,  so that it matches  all request
-              It does  not have path,  and we don't allow  empty path.
+              paths  under the  host  (e.g., specifying  "nghttp2.org"
-              To workaround  this, we  assume that CONNECT  method has
+              equals  to "nghttp2.org/").   CONNECT method  is treated
-              "/" as path.
+              specially.  It  does not have  path, and we  don't allow
+              empty path.  To workaround  this, we assume that CONNECT
+              method has "/" as path.
 
               Patterns with  host take  precedence over  patterns with
               just path.   Then, longer patterns take  precedence over
@@ -1811,6 +1813,11 @@ Connections:
               Optionally, TLS  can be disabled by  specifying "no-tls"
               parameter.  TLS is enabled by default.
 
+              If "sni-fwd" parameter is  used, when performing a match
+              to select a backend server,  SNI host name received from
+              the client  is used  instead of  the request  host.  See
+              --backend option about the pattern match.
+
               To  make this  frontend as  API endpoint,  specify "api"
               parameter.   This   is  disabled  by  default.    It  is
               important  to  limit the  access  to  the API  frontend.

src/shrpx_client_handler.cc

@@ -979,29 +979,30 @@ ClientHandler::get_downstream_connection(int &err, Downstream *downstream) {
   auto &balloc = downstream->get_block_allocator();
 
   // Fast path.  If we have one group, it must be catch-all group.
-  // proxy mode falls in this case.
   if (groups.size() == 1) {
     group_idx = 0;
-  } else if (req.method == HTTP_CONNECT) {
-    // CONNECT method does not have path.  But we requires path in
-    // host-path mapping.  As workaround, we assume that path is "/".
-    group_idx = match_downstream_addr_group(routerconf, req.authority,
-                                            StringRef::from_lit("/"), groups,
-                                            catch_all, balloc);
   } else {
-    if (!req.authority.empty()) {
+    StringRef authority;
-      group_idx = match_downstream_addr_group(
+    if (faddr_->sni_fwd) {
-          routerconf, req.authority, req.path, groups, catch_all, balloc);
+      authority = sni_;
+    } else if (!req.authority.empty()) {
+      authority = req.authority;
     } else {
       auto h = req.fs.header(http2::HD_HOST);
       if (h) {
-        group_idx = match_downstream_addr_group(routerconf, h->value, req.path,
+        authority = h->value;
-                                                groups, catch_all, balloc);
-      } else {
-        group_idx = match_downstream_addr_group(
-            routerconf, StringRef{}, req.path, groups, catch_all, balloc);
       }
     }
+
+    StringRef path;
+    // CONNECT method does not have path.  But we requires path in
+    // host-path mapping.  As workaround, we assume that path is "/".
+    if (req.method != HTTP_CONNECT) {
+      path = req.path;
+    }
+
+    group_idx = match_downstream_addr_group(routerconf, authority, path, groups,
+                                            catch_all, balloc);
   }
 
   if (LOG_ENABLED(INFO)) {

src/shrpx_config.cc

@@ -693,6 +693,7 @@ int parse_memcached_connection_params(MemcachedConnectionParams &out,
 struct UpstreamParams {
   int alt_mode;
   bool tls;
+  bool sni_fwd;
   bool proxyproto;
 };
 
@@ -708,6 +709,8 @@ int parse_upstream_params(UpstreamParams &out, const StringRef &src_params) {
 
     if (util::strieq_l("tls", param)) {
       out.tls = true;
+    } else if (util::strieq_l("sni-fwd", param)) {
+      out.sni_fwd = true;
     } else if (util::strieq_l("no-tls", param)) {
       out.tls = false;
     } else if (util::strieq_l("api", param)) {
@@ -2296,9 +2299,15 @@ int parse_config(Config *config, int optid, const StringRef &opt,
       return -1;
     }
 
+    if (params.sni_fwd && !params.tls) {
+      LOG(ERROR) << "frontend: sni_fwd requires tls";
+      return -1;
+    }
+
     UpstreamAddr addr{};
     addr.fd = -1;
     addr.tls = params.tls;
+    addr.sni_fwd = params.sni_fwd;
     addr.alt_mode = params.alt_mode;
     addr.accept_proxy_protocol = params.proxyproto;
 

src/shrpx_config.h

@@ -404,6 +404,9 @@ struct UpstreamAddr {
   bool host_unix;
   // true if TLS is enabled.
   bool tls;
+  // true if SNI host should be used as a host when selecting backend
+  // server.
+  bool sni_fwd;
   // true if client is supposed to send PROXY protocol v1 header.
   bool accept_proxy_protocol;
   int fd;