diff --git a/tools/gce_setup/grpc_docker.sh b/tools/gce_setup/grpc_docker.sh
index 2e7ed97a87f429ee9d63b35562f5bf7b12860042..44787b18e1bdcdeb32445a2bf22ab625986aeea5 100755
--- a/tools/gce_setup/grpc_docker.sh
+++ b/tools/gce_setup/grpc_docker.sh
@@ -822,7 +822,6 @@ grpc_interop_gen_ruby_cmd() {
   echo $the_cmd
 }
 
-
 # constructs the full dockerized java interop test cmd.
 #
 # call-seq:
@@ -832,12 +831,43 @@ grpc_cloud_prod_gen_ruby_cmd() {
   local cmd_prefix="sudo docker run grpc/ruby bin/bash -l -c"
   local test_script="/var/local/git/grpc/src/ruby/bin/interop/interop_client.rb"
   local test_script+=" --use_tls"
-  local gfe_flags=" --server_port=443 --server_host=grpc-test.sandbox.google.com --server_host_override=grpc-test.sandbox.google.com"
+  local gfe_flags=$(_grpc_prod_gfe_flags)
   local env_prefix="SSL_CERT_FILE=/cacerts/roots.pem"
   local the_cmd="$cmd_prefix '$env_prefix ruby $test_script $gfe_flags $@'"
   echo $the_cmd
 }
 
+# constructs the full dockerized ruby service_account auth interop test cmd.
+#
+# call-seq:
+#   flags= .... # generic flags to include the command
+#   cmd=$($grpc_gen_test_cmd $flags)
+grpc_cloud_prod_auth_service_account_creds_gen_ruby_cmd() {
+  local cmd_prefix="sudo docker run grpc/ruby bin/bash -l -c";
+  local test_script="/var/local/git/grpc/src/ruby/bin/interop/interop_client.rb"
+  local test_script+=" --use_tls"
+  local gfe_flags=$(_grpc_prod_gfe_flags)
+  local added_gfe_flags=$(_grpc_svc_acc_test_flags)
+  local env_prefix="SSL_CERT_FILE=/cacerts/roots.pem"
+  local the_cmd="$cmd_prefix '$env_prefix ruby $test_script $gfe_flags $added_gfe_flag $@'"
+  echo $the_cmd
+}
+
+# constructs the full dockerized ruby gce auth interop test cmd.
+#
+# call-seq:
+#   flags= .... # generic flags to include the command
+#   cmd=$($grpc_gen_test_cmd $flags)
+grpc_cloud_prod_auth_compute_engine_creds_gen_ruby_cmd() {
+  local cmd_prefix="sudo docker run grpc/ruby bin/bash -l -c";
+  local test_script="/var/local/git/grpc/src/ruby/bin/interop/interop_client.rb"
+  local test_script+=" --use_tls"
+  local gfe_flags=$(_grpc_prod_gfe_flags)
+  local added_gfe_flags=$(_grpc_gce_test_flags)
+  local env_prefix="SSL_CERT_FILE=/cacerts/roots.pem"
+  local the_cmd="$cmd_prefix '$env_prefix ruby $test_script $gfe_flags $added_gfe_flag $@'"
+  echo $the_cmd
+}
 
 # constructs the full dockerized Go interop test cmd.
 #
@@ -888,7 +918,7 @@ grpc_cloud_prod_gen_java_cmd() {
     local cmd_prefix="sudo docker run grpc/java";
     local test_script="/var/local/git/grpc-java/run-test-client.sh";
     local test_script+=" --use_tls=true"
-    local gfe_flags=" --server_port=443 --server_host=grpc-test.sandbox.google.com --server_host_override=grpc-test.sandbox.google.com"
+    local gfe_flags=$(_grpc_prod_gfe_flags)
     local the_cmd="$cmd_prefix $test_script $gfe_flags $@";
     echo $the_cmd
 }
@@ -909,19 +939,11 @@ grpc_interop_gen_php_cmd() {
     echo $the_cmd
 }
 
-# constructs the full dockerized cpp interop test cmd.
-#
+# constructs the full dockerized node interop test cmd.
 #
 # call-seq:
 #   flags= .... # generic flags to include the command
 #   cmd=$($grpc_gen_test_cmd $flags)
-grpc_interop_gen_cxx_cmd() {
-    local cmd_prefix="sudo docker run grpc/cxx";
-    local test_script="/var/local/git/grpc/bins/opt/interop_client --enable_ssl";
-    local the_cmd="$cmd_prefix $test_script $@";
-    echo $the_cmd
-}
-
 grpc_interop_gen_node_cmd() {
   local cmd_prefix="sudo docker run grpc/node";
   local test_script="/usr/bin/nodejs /var/local/git/grpc/src/node/interop/interop_client.js --use_tls=true";
@@ -931,46 +953,70 @@ grpc_interop_gen_node_cmd() {
 
 # constructs the full dockerized cpp interop test cmd.
 #
+# call-seq:
+#   flags= .... # generic flags to include the command
+#   cmd=$($grpc_gen_test_cmd $flags)
+grpc_interop_gen_cxx_cmd() {
+    local cmd_prefix="sudo docker run grpc/cxx";
+    local test_script="/var/local/git/grpc/bins/opt/interop_client --enable_ssl";
+    local the_cmd="$cmd_prefix $test_script $@";
+    echo $the_cmd
+}
+
+# constructs the full dockerized cpp gce=>prod interop test cmd.
 #
 # call-seq:
 #   flags= .... # generic flags to include the command
 #   cmd=$($grpc_gen_test_cmd $flags)
 grpc_cloud_prod_gen_cxx_cmd() {
     local cmd_prefix="sudo docker run grpc/cxx";
-    local test_script="/var/local/git/grpc/bins/opt/interop_client --enable_ssl";
-    local gfe_flags=" --use_prod_roots --server_port=443 --server_host=grpc-test.sandbox.google.com --server_host_override=grpc-test.sandbox.google.com"
+    local test_script="/var/local/git/grpc/bins/opt/interop_client --enable_ssl --use_prod_roots";
+    local gfe_flags=$(_grpc_prod_gfe_flags)
     local the_cmd="$cmd_prefix $test_script $gfe_flags $@";
     echo $the_cmd
 }
 
-# constructs the full dockerized cpp interop test cmd.
-#
+# constructs the full dockerized cpp service_account auth interop test cmd.
 #
 # call-seq:
 #   flags= .... # generic flags to include the command
 #   cmd=$($grpc_gen_test_cmd $flags)
 grpc_cloud_prod_auth_service_account_creds_gen_cxx_cmd() {
     local cmd_prefix="sudo docker run grpc/cxx";
-    local test_script="/var/local/git/grpc/bins/opt/interop_client --enable_ssl";
-    local gfe_flags=" --use_prod_roots --server_port=443 --server_host=grpc-test.sandbox.google.com --server_host_override=grpc-test.sandbox.google.com"
-    local added_gfe_flags=" --service_account_key_file=/service_account/stubbyCloudTestingTest-7dd63462c60c.json --oauth_scope=https://www.googleapis.com/auth/xapi.zoo"
+    local test_script="/var/local/git/grpc/bins/opt/interop_client --enable_ssl --use_prod_roots";
+    local gfe_flags=$(_grpc_prod_gfe_flags)
+    local added_gfe_flags=$(_grpc_svc_acc_test_flags)
     local the_cmd="$cmd_prefix $test_script $gfe_flags $added_gfe_flags $@";
     echo $the_cmd
 }
 
-# constructs the full dockerized cpp interop test cmd.
-#
+# constructs the full dockerized cpp gce auth interop test cmd.
 #
 # call-seq:
 #   flags= .... # generic flags to include the command
 #   cmd=$($grpc_gen_test_cmd $flags)
 grpc_cloud_prod_auth_compute_engine_creds_gen_cxx_cmd() {
     local cmd_prefix="sudo docker run grpc/cxx";
-    local test_script="/var/local/git/grpc/bins/opt/interop_client --enable_ssl";
-    local gfe_flags=" --use_prod_roots --server_port=443 --server_host=grpc-test.sandbox.google.com --server_host_override=grpc-test.sandbox.google.com"
-    local added_gfe_flags=" --default_service_account=155450119199-r5aaqa2vqoa9g5mv2m6s3m1l293rlmel@developer.gserviceaccount.com --oauth_scope=https://www.googleapis.com/auth/xapi.zoo"
+    local test_script="/var/local/git/grpc/bins/opt/interop_client --enable_ssl --use_prod_roots";
+    local gfe_flags=$(_grpc_prod_gfe_flags)
+    local added_gfe_flags=$(_grpc_gce_test_flags)
     local the_cmd="$cmd_prefix $test_script $gfe_flags $added_gfe_flags $@";
     echo $the_cmd
 }
 
-# TODO(grpc-team): add grpc_interop_gen_xxx_cmd for python|nodejs
+# outputs the flags passed to gfe tests
+_grpc_prod_gfe_flags() {
+  echo " --server_port=443 --server_host=grpc-test.sandbox.google.com --server_host_override=grpc-test.sandbox.google.com"
+}
+
+# outputs the flags passed to the service account auth tests
+_grpc_svc_acc_test_flags() {
+  echo " --service_account_key_file=/service_account/stubbyCloudTestingTest-7dd63462c60c.json --oauth_scope=https://www.googleapis.com/auth/xapi.zoo"
+}
+
+# outputs the flags passed to the gcloud auth tests
+_grpc_gce_test_flags() {
+  echo " --default_service_account=155450119199-r5aaqa2vqoa9g5mv2m6s3m1l293rlmel@developer.gserviceaccount.com --oauth_scope=https://www.googleapis.com/auth/xapi.zoo"
+}
+
+# TODO(grpc-team): add grpc_interop_gen_xxx_cmd for python
diff --git a/tools/gce_setup/shared_startup_funcs.sh b/tools/gce_setup/shared_startup_funcs.sh
index 3410a2a2c8aea0b401d715303d676c88ea897e08..eea940864da23295532426a4c363ce975cd68f83 100755
--- a/tools/gce_setup/shared_startup_funcs.sh
+++ b/tools/gce_setup/shared_startup_funcs.sh
@@ -372,7 +372,9 @@ grpc_dockerfile_install() {
 
   [[ -d $dockerfile_dir ]] || { echo "$FUNCNAME: not a valid dir: $dockerfile_dir"; return 1; }
 
-  # For specific base images, sync the ssh key into the .ssh dir in the dockerfile context
+  # For specific base images, sync private files.
+  #
+  # - the ssh key, ssh certs and/or service account info.
   [[ $image_label == "grpc/base" ]] && {
     grpc_docker_sync_github_key $dockerfile_dir/.ssh 'base_ssh_key' || return 1;
   }
@@ -384,6 +386,7 @@ grpc_dockerfile_install() {
   }
   [[ $image_label == "grpc/ruby" ]] && {
     grpc_docker_sync_roots_pem $dockerfile_dir/cacerts || return 1;
+    grpc_docker_sync_service_account $dockerfile_dir/service_account || return 1;
   }
   [[ $image_label == "grpc/cxx" ]] && {
     grpc_docker_sync_service_account $dockerfile_dir/service_account || return 1;