Use classic GAE for coordinator default frontend.

logdog/appengine/coordinator/service.go

 // Copyright 2015 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 package coordinator
 
 import (
         "sync"
         "sync/atomic"
         "time"
@@ skipping 239 matching lines @@
                 return nil, merr
         }
 
         // Get an Authenticator bound to the token scopes that we need for BigTable.
         creds, err := auth.GetPerRPCCredentials(auth.AsSelf, auth.WithScopes(bigtable.StorageScopes...))
         if err != nil {
                 log.WithError(err).Errorf(c, "Failed to create BigTable credentials.")
                 return nil, errors.New("failed to create BigTable credentials")
         }
 
+        // Use an AppEngine Context so we have access to the socket API. This is
+        // needed by AppEngine Classic for gRPC connections.
+        //
         // Explicitly clear gRPC metadata from the Context. It is forwarded to
         // delegate calls by default, and standard request metadata can break BigTable
         // calls.
-        c = metadata.NewContext(c, nil)
-
-        st, err := bigtable.New(c, bigtable.Options{
+        st, err := bigtable.New(metadata.NewContext(s.aeCtx, nil), bigtable.Options{
                 Project:  bt.Project,
                 Instance: bt.Instance,
                 LogTable: bt.LogTableName,
                 ClientOptions: []option.ClientOption{
                         option.WithGRPCDialOption(grpc.WithPerRPCCredentials(creds)),
                 },
                 Cache: s.getStorageCache(),
         })
         if err != nil {
                 log.WithError(err).Errorf(c, "Failed to create BigTable instance.")
@@ skipping 272 matching lines @@
 
         // Sign index URL.
         if req.Index {
                 if resp.Index, err = doSign(si.index); err != nil {
                         return nil, errors.Annotate(err).InternalReason("failed to sign index URL").Err()
                 }
         }
 
         return &resp, nil
 }