Configuring a gRPC Service

To create a gRPC service—whether or not you are using API Gateway—you specify the interface definition in one or more proto files, which are text files with the .proto extension. In a proto file, you define the surface of your API, including the data structures, methods, method parameters, and return types. Then, you compile your proto file by using the language-specific protocol buffer compiler, protoc. For more information, see What is gRPC? and gRPC concepts.

To have your gRPC service managed by API Gateway, in addition to the compiled proto file, you have to specify a service configuration in one or more YAML files. A service configuration is a specification that lets you define the behavior of a gRPC service, including authentication, quotas, and more.

Service configuration overview

At the top of the YAML file, you can specify basic information about the service, such as its name and title. Other aspects of the service are configured in subsections of the YAML file, for example:

For example:

type: google.api.Service
config_version: 3
title: Google Calendar API
- name: google.calendar.v3.Calendar
  - id: google_calendar_auth
  - selector: "*"
      provider_id: google_calendar_auth
    - selector: "*"
      address: grpcs://

Each subsection typically corresponds to a .proto message where you configure various aspects of the service. For example:

  • authentication: specifies how callers are authenticated.
  • backend: controls remote backend routing.
  • http: defines the rules for mapping an RPC method to one or more HTTP REST API methods.
  • usage: lets you selectively enable and disable API key validation.

The official schema for the service configuration is defined by the .proto message google.api.Service.

Basic configuration

The Bookstore sample, which is used in the Getting started with API Gateway and Cloud Run for gRPC tutorial, includes a basic interface definition file and a service configuration file.

The Bookstore interface definition, bookstore.proto:

syntax = "proto3";

package endpoints.examples.bookstore;

option java_multiple_files = true;
option java_outer_classname = "BookstoreProto";
option java_package = "";

import "google/protobuf/empty.proto";

service Bookstore {
  rpc ListShelves(google.protobuf.Empty) returns (ListShelvesResponse) {}
  rpc CreateShelf(CreateShelfRequest) returns (Shelf) {}
  rpc GetShelf(GetShelfRequest) returns (Shelf) {}
  rpc DeleteShelf(DeleteShelfRequest) returns (google.protobuf.Empty) {}
  rpc ListBooks(ListBooksRequest) returns (ListBooksResponse) {}
  rpc CreateBook(CreateBookRequest) returns (Book) {}
  rpc GetBook(GetBookRequest) returns (Book) {}
  rpc DeleteBook(DeleteBookRequest) returns (google.protobuf.Empty) {}

message Shelf {
  int64 id = 1;
  string theme = 2;

message Book {
  int64 id = 1;
  string author = 2;
  string title = 3;

The Bookstore service configuration, api_config.yaml:

type: google.api.Service
config_version: 3

name: *

title: Bookstore gRPC API
- name: endpoints.examples.bookstore.Bookstore

The previous code sample is the simplest service configuration as it:

  • Defines a service named * where PROJECT_ID is the name of your Google Cloud project ID.
  • Specifies that the service exposes the API endpoints.examples.bookstore.Bookstore, as defined in the bookstore.proto file.

Rules and selectors

In some cases, you might need the ability to associate configuration with individual elements of a service—for example, to enforce authentication on certain methods but not others. To configure this in your service configuration, some parts of the service configuration, such as authentication and http, let you specify rules and selectors. A selector identifies the elements of the service, such as a method name that the configuration associated with the rule applies to.

A selector is a comma-separated list of qualified names defined in the service: method, message, field, enum, or enum values. The last segment of the name can be the wildcard *, which matches any suffix. Wildcards are allowed only at the end of a name and only for a whole segment of the name. For example: foo.* is okay, but not foo.b* or foo.*.bar. To configure a default for all applicable elements, you specify * by itself.

Example 1 (affecting entire service):

  # Allow unregistered calls for all methods.
  - selector: "*"
    allow_unregistered_calls: true

Example 2 (affecting a single method):

  # Disable API key validation on just the ListShelves method
  # while requiring an API key for the rest of the API.
  - selector: "*"
    allow_unregistered_calls: false
  - selector: "endpoints.examples.bookstore.BookStore.ListShelves"
    allow_unregistered_calls: true

The previous example shows how to require API key validation for all methods except the ListShelves method.

Rules are evaluated sequentially, the last matching one in the declaration order is applied.

Using multiple YAML files

You might find it useful to use more than one YAML file to configure different features for the same service. Using multiple YAML files makes it easier to reuse files and modify them for different environments. For example, in the Bookstore sample, the basic configuration is specified in the api_config.yaml file and its HTTP rules are specified in the api_config_http.yaml file. This lets you deploy the HTTP rules only if you want to turn on JSON/HTTP to gRPC transcoding for the Bookstore.

If you use multiple YAML files for your service configuration, when the configuration is deployed each file is converted to google.api.Service proto messages, and then all messages are merged using proto merging semantics. That is, all singular scalar fields in the latter instance replace those in the former. So if you provide different singular values for the same rule in two files, the value in the second file you specify when deploying the configuration is used. Singular embedded messages are merged, and repeated fields are concatenated.

Like rules, merging is order sensitive. If there are two service configurations, the second service configuration overrides the first one.

Annotations (HTTP rules only)

As an alternative to using a YAML file for configuring HTTP options, you can configure them directly in your proto file, using the options mechanism. API annotations are defined in annotations.proto.

Use annotations if the configuration option is intended to be invariant over all usages of the protocol buffer interface definition. For example, if an API has one single implementation, or all implementations are required to have the same HTTP interface, you can annotate the HTTP configuration in the proto file.

If a configuration option is provided, both in the proto file and the service configuration YAML file, the service configuration overrides the annotation.

Example annotation in a proto file:

rpc ListShelves(google.protobuf.Empty) returns (ListShelvesResponse) {
    option (google.api.http) = { get: "/v1/shelves" };

# The preceding annotation is equivalent to the following service configuration:

  - selector: endpoints.examples.bookstore.BookStore.ListShelves
    get: '/v1/shelves'

For more information, see Transcoding HTTP/JSON to gRPC.

What's next