Spring boot starter for gRPC framework.

Table of Contents

• 1. Features
• 2. Setup
  • 2.1. Long story short
  • 2.2. Short story long
• 3. Usage
• 4. Showcase
  • 4.1. Service implementation
  • 4.2. Interceptors support
  • 4.3. Distributed tracing support (Spring Cloud Sleuth integration)
  • 4.4. GRPC server metrics (Micrometer.io integration)
  • 4.5. Spring Boot Validation support
  • 4.6. Spring cloud stream support
  • 4.7. Spring security support
  • 4.8. Transport Security (TLS)
  • 4.9. Custom gRPC Server Configuration
• 5. Events
• 6. Reactive API support
• 7. Error handling
• 8. Implementing message validation
• 9. GRPC response observer and Spring @Transactional caveats
• 10. Spring Security Integration
  • 10.1. Setup
  • 10.2. Server side configuration
  • 10.3. @PreAuthorize() and @PostAuthorize() support
  • 10.4. Obtaining Authentication details
  • 10.5. Client side configuration support
• 11. Health check
• 12. Spring actuator support
• 13. Consul Integration
• 14. Eureka Integration
  • 14.1. gRPC Server Project
  • 14.2. gRPC Client Project
• 15. License

1. Features

Autoconfigures and runs the embedded gRPC server with @GRpcService-enabled beans as part of spring-boot application (short video)

2. Setup

2.1. Long story short

Gradle users are advised to apply the plugin :

plugins {
id "io.github.lognet.grpc-spring-boot" version '5.1.5'
}

io.github.lognet.grpc-spring-boot gradle plugin dramatically simplifies the project setup.

2.2. Short story long

repositories {
  mavenCentral()
  // maven { url "https://oss.sonatype.org/content/repositories/snapshots" } // for snapshot builds
}
dependencies {
  implementation 'io.github.lognet:grpc-spring-boot-starter:5.1.5'
}

By default, starter pulls io.grpc:grpc-netty-shaded as transitive dependency, if you are forced to use pure grpc-netty dependency:

implementation ('io.github.lognet:grpc-spring-boot-starter:5.1.5') {
  exclude group: 'io.grpc', module: 'grpc-netty-shaded'
}
implementation 'io.grpc:grpc-netty:1.58.0' // (1)

1. Make sure to pull the version that matches the release.

Both libraries' presence on classpath is also supported with grpc.netty-server.on-collision-prefer-shaded-netty property.

If you are using Spring Boot Dependency Management plugin, it might pull not the same version as the version this started was compiled against, causing binary incompatibility issue.
In this case you’ll need to forcibly and explicitly set the grpc version to use (see version matrix here ):

configurations.all {
  resolutionStrategy.eachDependency { details ->
    if ("io.grpc".equalsIgnoreCase(details.requested.group)) {
      details.useVersion "1.58.0"
    }
  }
}

ℹ️	The release notes with compatibility matrix can be found here

Follow this guide to generate stub and server interface(s) from your .proto file(s).

If you are stack with maven - use this link.

3. Usage

• Annotate your server interface implementation(s) with @org.lognet.springboot.grpc.GRpcService

• Optionally configure the server port in your application.yml/properties. Default port is 6565.

 grpc:
    port: 6565

ℹ️	A random port can be defined by setting the port to 0. The actual port being used can then be retrieved by using @LocalRunningGrpcPort annotation on int field which will inject the running port (explicitly configured or randomly selected)

• Optionally enable server reflection (see https://github.com/grpc/grpc-java/blob/master/documentation/server-reflection-tutorial.md)

 grpc:
    enableReflection: true

• Optionally set the startup phase order (defaults to Integer.MAX_VALUE).

 grpc:
    start-up-phase: XXX

• Optionally set the number of seconds to wait for preexisting calls to finish during graceful server shutdown. New calls will be rejected during this time. A negative value is equivalent to an infinite grace period. Default value is 0 (means don’t wait).

 grpc:
    shutdownGrace: 30

• Netty-specific server properties can be specified under grpc.netty-server prefix.
  By configuring one of the grpc.netty-server.xxxx values you are implicitly setting transport to be Netty-based.

grpc:
  netty-server:
    keep-alive-time: 30s (1)
    max-inbound-message-size: 10MB (2)
    primary-listen-address: 10.10.15.23:0 (3)
    additional-listen-addresses:
      - 192.168.0.100:6767 (4)
    on-collision-prefer-shaded-netty: false (5)

1. Duration type properties can be configured with string value format described here.

2. DataSize type properties can be configured with string value described here

3. Exposed on external network IP with custom port.
   SocketAddress type properties string value format:

   • host:port (if port value is less than 1, uses random value)

   • host: (uses default grpc port, 6565 )

4. Exposed on internal network IP as well with predefined port 6767.

5. In case you have both shaded and pure netty libraries in dependencies, pick the NettyServerBuilder type that should be created. This is the type that will be passed to GRpcServerBuilderConfigurer (see Custom gRPC Server Configuration), defaults to true(i.e. io.grpc.netty.shaded.io.grpc.netty.NettyServerBuilder; io.grpc.netty.NettyServerBuilder if false)

The starter supports also the in-process server, which should be used for testing purposes :

 grpc:
    enabled: false (1)
    inProcessServerName: myTestServer (2)

1. Disables the default server (NettyServer).

2. Enables the in-process server.

ℹ️	If you enable both the NettyServer and in-process server, they will both share the same instance of HealthStatusManager and GRpcServerBuilderConfigurer (see Custom gRPC Server Configuration).

4. Showcase

In the grpc-spring-boot-starter-demo project you can find fully functional examples with integration tests.

4.1. Service implementation

The service definition from .proto file looks like this :

service Greeter {
    rpc SayHello ( HelloRequest) returns (  HelloReply) {}
}

Note the generated io.grpc.examples.GreeterGrpc.GreeterImplBase class that extends io.grpc.BindableService.

All you need to do is to annotate your service implementation with @org.lognet.springboot.grpc.GRpcService

    @GRpcService
    public static class GreeterService extends  GreeterGrpc.GreeterImplBase{
        @Override
        public void sayHello(GreeterOuterClass.HelloRequest request, StreamObserver<GreeterOuterClass.HelloReply> responseObserver) {
            final GreeterOuterClass.HelloReply.Builder replyBuilder = GreeterOuterClass.HelloReply.newBuilder().setMessage("Hello " + request.getName());
            responseObserver.onNext(replyBuilder.build());
            responseObserver.onCompleted();
        }
    }

4.2. Interceptors support

The starter supports the registration of two kinds of interceptors: Global and Per Service.
In both cases the interceptor has to implement io.grpc.ServerInterceptor interface.

• Per service

@GRpcService(interceptors = { LogInterceptor.class })
public  class GreeterService extends  GreeterGrpc.GreeterImplBase{
    // ommited
}

LogInterceptor will be instantiated via spring factory if there is bean of type LogInterceptor, or via no-args constructor otherwise.

• Global

@GRpcGlobalInterceptor
public  class MyInterceptor implements ServerInterceptor{
    // ommited
}

The annotation on java config factory method is also supported :

 @Configuration
 public class MyConfig{
     @Bean
     @GRpcGlobalInterceptor
     public  ServerInterceptor globalInterceptor(){
         return new ServerInterceptor(){
             @Override
             public <ReqT, RespT> ServerCall.Listener<ReqT> interceptCall(ServerCall<ReqT, RespT> call, Metadata headers, ServerCallHandler<ReqT, RespT> next) {
                // your logic here
                 return next.startCall(call, headers);
             }
         };
     }
 }

The particular service also has the opportunity to disable the global interceptors :

@GRpcService(applyGlobalInterceptors = false)
public  class GreeterService extends  GreeterGrpc.GreeterImplBase{
    // ommited
}

4.2.1. Interceptors ordering

Global interceptors can be ordered using Spring’s @Ordered or @Priority annotations. Following Spring’s ordering semantics, lower order values have higher priority and will be executed first in the interceptor chain.

@GRpcGlobalInterceptor
@Order(10)
public  class A implements ServerInterceptor{
    // will be called before B
}

@GRpcGlobalInterceptor
@Order(20)
public  class B implements ServerInterceptor{
    // will be called after A
}

The starter uses built-in interceptors to implement error handling, Spring Security, Validation and Metrics integration. Their order can also be controlled by below properties :

• grpc.recovery.interceptor-order (error handling interceptor order, defaults to Ordered.HIGHEST_PRECEDENCE)

• grpc.security.auth.interceptor-order ( defaults to Ordered.HIGHEST_PRECEDENCE+1)

• grpc.validation.interceptor-order ( defaults to Ordered.HIGHEST_PRECEDENCE+10)

• grpc.metrics.interceptor-order ( defaults to Ordered.HIGHEST_PRECEDENCE+20)

This gives you the ability to set up the desired order of built-in and your custom interceptors.

Keep on reading !!! There is more

The way grpc interceptor works is that it intercepts the call and returns the server call listener, which in turn can intercept the request message as well, before forwarding it to the actual service call handler :

By setting grpc.security.auth.fail-fast property to false all downstream interceptors as well as all upstream interceptors (On_Message) will still be executed in case of authentication/authorization failure

Assuming interceptor_2 is securityInterceptor :

• For failed authentication/authorization with grpc.security.auth.fail-fast=true(default):
  

  

• For failed authentication/authorization with grpc.security.auth.fail-fast=false:
  

  

4.3. Distributed tracing support (Spring Cloud Sleuth integration)

This started is natively supported by spring-cloud-sleuth project.
Please continue to sleuth grpc integration.

4.4. GRPC server metrics (Micrometer.io integration)

By including org.springframework.boot:spring-boot-starter-actuator dependency, the starter will collect gRPC server metrics , broken down by

1. method - gRPC service method FQN (Fully Qualified Name)

2. result - Response status code

3. address - server local address (if you exposed additional listen addresses, with grpc.netty-server.additional-listen-addresses property)

After configuring the exporter of your choice, you should see the timer named grpc.server.calls.

4.4.1. Custom tags support

By defining GRpcMetricsTagsContributor bean in your application context, you can add custom tags to the grpc.server.calls timer.
You can also use RequestAwareGRpcMetricsTagsContributor bean to tag unary and streaming calls.
Demo is here

💡	Keep the dispersion low not to blow up the cardinality of the metric.

RequestAwareGRpcMetricsTagsContributor can be still executed for failed authentication if metric interceptor has higher precedence than security interceptor and grpc.security.auth.fail-fast set to false.
This case is covered by this test.

💡	Make sure to read Interceptors ordering chapter.

4.4.2. Exposing Prometheus endpoint

Make sure to include below dependencies :

implementation "org.springframework.boot:spring-boot-starter-actuator"
implementation "io.micrometer:micrometer-registry-prometheus"
implementation 'org.springframework.boot:spring-boot-starter-web'

Configuration :

management:
  metrics:
    export:
      prometheus:
        enabled: true
  endpoints:
    web:
      exposure:
        include: "*"

Standard /actuator/metrics and /actuator/prometheus endpoints will render grpc.server.calls metrics (see demo here).

ℹ️	GRPC scrapping proposal

4.5. Spring Boot Validation support

The starter can be autoconfigured to validate request/response gRPC service messages. Please continue to Implementing message validation for configuration details.

4.6. Spring cloud stream support

The starter internally defines the bean of type java.util.function.Consumer which is being considered for function registry when spring-cloud-stream is on classpath, which is undesirable (spring-cloud-stream auto-registers the channel if you have exactly one Consumer/Supplier/Function bean in the application context, so you already have one if you use this starter together with spring-cloud-stream).

According to this, it is recommended to use spring.cloud.function.definition property in production ready applications and not to rely on the auto-discovery.

Please refer to GRPC Kafka Stream demo, the essential part is this line.

4.7. Spring security support

The starter provides built-in support for authenticating and authorizing users leveraging integration with Spring Security framework.
Please refer to the sections on Spring Security Integration for details on supported authentication providers and configuration options.

4.8. Transport Security (TLS)

The transport security can be configured using root certificate together with its private key path:

 grpc:
    security:
      cert-chain: classpath:cert/server-cert.pem
      private-key: file:../grpc-spring-boot-starter-demo/src/test/resources/cert/server-key.pem

The value of both properties is in form supported by ResourceEditor.

The client side should be configured accordingly :

((NettyChannelBuilder)channelBuilder)
 .useTransportSecurity()
 .sslContext(GrpcSslContexts.forClient().trustManager(certChain).build());

This starter will pull the io.netty:netty-tcnative-boringssl-static dependency by default to support SSL.
If you need another SSL/TLS support, please exclude this dependency and follow Security Guide.

ℹ️	If the more detailed tuning is needed for security setup, please use custom configurer described in Custom gRPC Server Configuration

4.9. Custom gRPC Server Configuration

To intercept the io.grpc.ServerBuilder instance used to build the io.grpc.Server, you can add bean that inherits from org.lognet.springboot.grpc.GRpcServerBuilderConfigurer to your context and override the configure method.
Multiple configurers are also supported.
By the time of invocation of configure method, all discovered services, including theirs interceptors, had been added to the passed builder.
In your implementation of configure method, you can add your custom configuration:

@Component
public class MyGRpcServerBuilderConfigurer extends GRpcServerBuilderConfigurer{
        @Override
        public void configure(ServerBuilder<?> serverBuilder){
            serverBuilder
                .executor(YOUR EXECUTOR INSTANCE)
                .useTransportSecurity(YOUR TRANSPORT SECURITY SETTINGS);
            ((NettyServerBuilder)serverBuilder)// cast to NettyServerBuilder (which is the default server) for further customization
                    .sslContext(GrpcSslContexts  // security fine tuning
                                    .forServer(...)
                                    .trustManager(...)
                                    .build())
                    .maxConnectionAge(...)
                    .maxConnectionAgeGrace(...);

        }
    };
}
@Component
public class MyCustomCompressionGRpcServerBuilderConfigurer extends GRpcServerBuilderConfigurer{
        @Override
        public void configure(ServerBuilder<?> serverBuilder){
            serverBuilder
                .compressorRegistry(YOUR COMPRESSION REGISTRY)
                .decompressorRegistry(YOUR DECOMPRESSION REGISTRY) ;

        }
    };
}

ℹ️	If you enable both NettyServer and in-process servers, the configure method will be invoked on the same instance of configurer. If you need to differentiate between the passed serverBuilder s, you can check the type. This is the current limitation.

5. Events

GRpcServerInitializedEvent is published upon server startup, you can consume it using regular spring API.

6. Reactive API support

Starting from version 5.1.0, spring-boot-starter-gradle-plugin integrates SalesForce’s reactive-grpc protoc plugin :

import org.lognet.springboot.grpc.gradle.ReactiveFeature
plugins {
  id "io.github.lognet.grpc-spring-boot"
}
grpcSpringBoot {
  reactiveFeature.set(ReactiveFeature.REACTOR) // or ReactiveFeature.RX
}

Here are the tests and reactive grpc sample service.

7. Error handling

The starter registers the GRpcExceptionHandlerInterceptor which is responsible to propagate the service-thrown exception to the error handlers.
The error handling method could be registered by having @GRpcServiceAdvice annotated bean with methods annotated with @GRpcExceptionHandler annotations.
These are considered as global error handlers and the method with exception type parameter the nearest by the type hierarchy to the thrown exception is invoked.
The signature of the error handler has to follow the below pattern:

Return type	Parameter 1	Parameter 2
io.grpc.Status	any Exception type	GRpcExceptionScope

Sample

@GRpcServiceAdvice
class MyHandler1{
    @GRpcExceptionHandler
    public Status handle (MyCustomExcpetion exc, GRpcExceptionScope scope){

    }
    @GRpcExceptionHandler
    public Status handle (IllegalArgumentException exc, GRpcExceptionScope scope){

    }

}
@GRpcServiceAdvice
class MyHandler2 {
    @GRpcExceptionHandler
   public Status anotherHandler (NullPointerException npe,GRpcExceptionScope scope){

   }
}

You can have as many advice beans and handler methods as you want as long as they don’t interfere with each other and don’t create handled exception type ambiguity.

The grpc service bean is also discovered for error handlers, having the higher precedence than global error handling methods discovered in @GRpcServiceAdvice beans. The service-level error handling methods are considered private and invoked only when the exception is thrown by this service:

Sample

class SomeException extends Exception{

}
class SomeRuntimeException extends RuntimeException{

}

@GRpcService
public  class HelloService extends GreeterGrpc.GreeterImplBase{
    @Override
    public void sayHello(GreeterOuterClass.HelloRequest request, StreamObserver<GreeterOuterClass.HelloReply> responseObserver) {
        ...
    throw new GRpcRuntimeExceptionWrapper(new SomeException()) ; // (1)
//or
    throw new GRpcRuntimeExceptionWrapper(new SomeException(), "myHint");// (2)
//or
    throw new SomeRuntimeException(); //(3)
    }
   @GRpcExceptionHandler
   public Status privateHandler (SomeException npe,GRpcExceptionScope scope){
        // INVOKED when thrown from  HelloService service
        String myHint = scope.getHintAs(String.class);   // (4)
        scope.getResponseHeaders().put(Metadata.Key.of("custom", Metadata.ASCII_STRING_MARSHALLER), "Value");// (5)
   }
   @GRpcExceptionHandler
   public Status privateHandler (SomeRuntimeException npe,GRpcExceptionScope scope){
        // INVOKED when thrown from  HelloService service

   }
}
@GRpcServiceAdvice
class MyHandler  {
   @GRpcExceptionHandler
   public Status anotherHandler (SomeException npe,GRpcExceptionScope scope){
        // NOT INVOKED when thrown from  HelloService service
   }
   @GRpcExceptionHandler
   public Status anotherHandler (SomeRuntimeException npe,GRpcExceptionScope scope){
        // NOT INVOKED when thrown from  HelloService service
   }

}

1. Because the nature of grpc service API that doesn’t allow throwing checked exception, the special runtime exception type is provided to wrap the checked exception. It’s then getting unwrapped when looking for the handler method.

2. When throwing the GRpcRuntimeExceptionWrapper exception, you can also pass the hint object which is then accessible from the scope object in handler method.

3. Runtime exception can be thrown as-is and doesn’t need to be wrapped.

4. Obtain the hint object.

5. Send custom headers to the client.

Authentication failure is propagated via AuthenticationException and authorization failure - via AccessDeniedException.

Validation failure is propagated via ConstraintViolationException: for failed request - with Status.INVALID_ARGUMENT as a hint , and for failed response - with Status.FAILED_PRECONDITION as a hint.

The demo is here

8. Implementing message validation

Thanks to Bean Validation configuration support via XML deployment descriptor , it’s possible to provide the constraints for generated classes via XML instead of instrumenting the generated messages with custom protoc compiler.

1. Add org.springframework.boot:spring-boot-starter-validation dependency to your project.

2. Create META-INF/validation.xml and constraints declarations file(s). (IntelliJ IDEA has great auto-complete support for authorizing bean validation constraints xml files )
   See also samples from Hibernate validator documentation

You can find demo configuration and corresponding tests here

Note, that both request and response messages are being validated.

If your gRPC method uses the same request and response message type, you can use org.lognet.springboot.grpc.validation.group.RequestMessage and org.lognet.springboot.grpc.validation.group.ResponseMessage validation groups to apply different validation logic :

...
<getter name="someField">
	<!--should be empty for request message-->
	<constraint annotation="javax.validation.constraints.Size">
		<groups>
			<value>org.lognet.springboot.grpc.validation.group.RequestMessage</value> (1)
		</groups>
		<element name="min">0</element>
		<element name="max">0</element>
	</constraint>
	<!--should NOT  be empty for response message-->
	<constraint annotation="javax.validation.constraints.NotEmpty">
		<groups>
			<value>org.lognet.springboot.grpc.validation.group.ResponseMessage</value> (2)
		</groups>
	</constraint>
</getter>
...

1. Apply this constraint only for request message

2. Apply this constraint only for response message

Note also custom cross-field constraint and its usage :

<bean class="io.grpc.examples.GreeterOuterClass$Person">
	<class>
		<constraint annotation="org.lognet.springboot.grpc.demo.PersonConstraint"/>
	</class>
    <!-- ... -->
</bean>

As described in Interceptors ordering chapter, you can give validation interceptor the higher precedence than security interceptor and set grpc.security.auth.fail-fast property to false.
In this scenario, if call is both unauthenticated and invalid, the client will get Status.INVALID_ARGUMENT instead of Status.PERMISSION_DENIED/Status.UNAUTHENTICATED response status. Demo is here

9. GRPC response observer and Spring @Transactional caveats

While it’s still possible to have your rpc methods annotated with @Transactional (with spring.aop.proxy-target-class=true if it’s not enabled by default), chances are to get unpredictable behaviour. Consider below grpc method implementation :

@GRpcService
class MyGrpcService extends ...{
    @Autowired
    private MyJpaRepository repo;

    @Transactional //(1)
    public void rpcCall(Req request, StreamOvserver<Res> observer) {
        Res response = // Database operations via repo
        observer.onNext(response); //(2)
        observer.onCompleted();
    }//(3)
}

1. The method is annotated as @Transactional, Spring will commit the transaction at some time after methods returns

2. Response is returned to the caller

3. Methods returns, transaction eventually committed.

Theoretically, and as you can see - practically, there is small time-span when client (if the network latency is minimal, and your grpc server encouraged context switch right after <2>) can try to access the database via another grpc call before the transaction is committed.

The solution to overcome this situation is to externalize the transactional logic into separate service class :

@Service
class MyService{
    @Autowired
    private MyJpaRepository repo;

    @Transactional //(1)
    public Res doTransactionalWork(){
        // Database operations via repo
        return result;
    }//(2)
}
@GRpcService
class MyGrpcService extends ...{
    @Autowired
    private MyService myService;

    public void rpcCall(Req request, StreamOvserver<Res> observer) {
        Res response = myService.doTransactionalWork();
        observer.onNext(response); //(3)
        observer.onCompleted();
    }
}

1. Service method is transactional

2. Transaction is eventually committed.

3. Reply after transaction is committed.

By following this approach you also decouple the transport layer and business logic that now can be tested separately.

10. Spring Security Integration

10.1. Setup

Table 1. Dependencies to implement authentiction scheme (to be added to server-side project)

Scheme	Dependencies
Basic	org.springframework.security:spring-security-config
Bearer	org.springframework.security:spring-security-config org.springframework.security:spring-security-oauth2-jose org.springframework.security:spring-security-oauth2-resource-server
Custom	org.springframework.security:spring-security-config your.custom.lib

10.2. Server side configuration

GRPC security configuration follows the same principals and APIs as Spring WEB security configuration, it’s enabled by default if you have org.springframework.security:spring-security-config dependency in your classpath.

You can use @Secured annotation on services/methods to protect your endpoints, or by using API and overriding defaults (which precesses @Secured annotation ):

 @Configuration
   class MySecurityCfg extends GrpcSecurityConfigurerAdapter {
        @Override
        public void configure(GrpcSecurity builder) throws Exception {
            MethodsDescriptor<?,?> adminMethods = MyServiceGrpc.getSomeMethod();
            builder
                    .authorizeRequests()
                    .methods(adminMethods).hasAnyRole("admin")
                    .anyMethodExcluding(adminMethods).hasAnyRole("user")
                    .withSecuredAnnotation();(1)
        }
    }

1. or combine API with @Secured annotations.

10.2.1. Default

This default configuration secures GRPC methods/services annotated with org.springframework.security.access.annotation.@Secured annotation.
Leaving value of the annotation empty (@Secured({})) means : authenticate only, no authorization will be performed.

If JwtDecoder bean exists in your context, it will also register JwtAuthenticationProvider to handle the validation of authentication claim.

BasicAuthSchemeSelector and BearerTokenAuthSchemeSelector are also automatically registered to support authentication with username/password and bearer token.

By setting grpc.security.auth.enabled to false, GRPC security can be turned-off.

10.2.2. Custom

Customization of GRPC security configuration is done by extending GrpcSecurityConfigurerAdapter (Various configuration examples and test scenarios are here.)

    @Configuration
    public class GrpcSecurityConfiguration extends GrpcSecurityConfigurerAdapter {
        @Autowired
        private JwtDecoder jwtDecoder;

        @Override
        public void configure(GrpcSecurity builder) throws Exception {

            builder.authorizeRequests()(1)
                    .methods(GreeterGrpc.getSayHelloMethod()).hasAnyAuthority("SCOPE_profile")(2)
            .and()
                    .authenticationProvider(JwtAuthProviderFactory.withAuthorities(jwtDecoder));(3)
        }
    }

1. Get hold of authorization configuration object

2. MethodDefinition of sayHello method is allowed for authenticated users with SCOPE_profile authority.

3. Use JwtAuthenticationProvider to validate user claim (BEARER token) against resource server configured with spring.security.oauth2.resourceserver.jwt.issuer-uri property.

10.2.3. DIY

One is possible to plug in your own bespoke authentication provider by implementing AuthenticationSchemeSelector interface.

@Configuration
    public class GrpcSecurityConfiguration extends GrpcSecurityConfigurerAdapter {
    @Override
        public void configure(GrpcSecurity builder) throws Exception {
        builder.authorizeRequests()
                    .anyMethod().authenticated()//(1)
                    .and()
                    .authenticationSchemeSelector(new AuthenticationSchemeSelector() { //(2)
                            @Override
                            public Optional<Authentication> getAuthScheme(CharSequence authorization) {
                                return new MyAuthenticationObject();// (3)
                            }
                        })
                    .authenticationProvider(new AuthenticationProvider() {// (4)
                        @Override
                        public Authentication authenticate(Authentication authentication) throws AuthenticationException {
                            MyAuthenticationObject myAuth= (MyAuthenticationObject)authentication;
                            //validate myAuth
                            return MyValidatedAuthenticationObject(withAuthorities);//(5)
                        }

                        @Override
                        public boolean supports(Class<?> authentication) {
                            return MyAuthenticationObject.class.isInstance(authentication);
                        }
                    });
 }
 }

1. Secure all services methods.

2. Register your own AuthenticationSchemeSelector.

3. Based on provided authorization header - return Authentication object as a claim (not authenticated yet)

4. Register your own AuthenticationProvider that supports validation of MyAuthenticationObject

5. Validate provided authentication and return validated and authenticated Authentication object

AuthenticationSchemeSelector can also be registered by defining Spring bean in your application context:

@Bean
public AuthenticationSchemeSelector myCustomSchemeSelector(){
     return authHeader->{
         // your logic here
     };
}

Client side configuration support section explains how to pass custom authorization scheme and claim from GRPC client.

10.3. @PreAuthorize() and @PostAuthorize() support

Starting from version 4.5.9 you can also use standard @PreAuthorize and @PostAuthorize annotations on grpc service methods and grpc service types.

Table 2. Referencing input/output object in expression

Call Type	Input object ref	Output object ref	Sample
Unary (request-response)	By parameter name	returnObject	@Override @PreAuthorize("#person.age<12") @PostAuthorize("returnObject.description.length()>0") public void unary(Person person, StreamObserver<Assignment> responseObserver) { }
Input stream, single response	#p0 or #a0	returnObject	@Override @PreAuthorize("#p0.getAge()<12") @PostAuthorize("returnObject.description.length()>0") public StreamObserver<Person> inStream(StreamObserver<Assignment> responseObserver) { }
Single request, output stream	By parameter name	returnObject	@Override @PreAuthorize("#person.age<12") @PostAuthorize("returnObject.description.length()>0") public void outStream(Person person, StreamObserver<Assignment> responseObserver) { }
Bidi stream	#p0 or #a0	returnObject	@Override @PreAuthorize("#p0.age<12") @PostAuthorize("returnObject.description.length()>0") public StreamObserver<Person> bidiStream(StreamObserver<Assignment> responseObserver) { }

10.4. Obtaining Authentication details

To obtain Authentication object in the implementation of secured method, please use below snippet

final Authentication auth = GrpcSecurity.AUTHENTICATION_CONTEXT_KEY.get();

Starting from 4.5.6, the Authentication object can also be obtained via standard Spring API :

final Authentication auth = SecurityContextHolder.getContext().getAuthentication();

10.5. Client side configuration support

By adding io.github.lognet:grpc-client-spring-boot-starter dependency to your java grpc client application you can easily configure per-channel or per-call credentials :

Per-channel

class MyClient{
    public void doWork(){
        final AuthClientInterceptor clientInterceptor = new AuthClientInterceptor((1)
                AuthHeader.builder()
                    .bearer()
                    .binaryFormat(true)(3)
                    .tokenSupplier(this::generateToken)(4)
        );

        Channel authenticatedChannel = ClientInterceptors.intercept(
                ManagedChannelBuilder.forAddress("host", 6565).build(), clientInterceptor (2)
        );
        // use authenticatedChannel to invoke GRPC service
    }

     private ByteBuffer generateToken(){ (4)
         // generate bearer token against your resource server
     }
 }

1. Create client interceptor

2. Intercept channel

3. Turn the binary format on/off:
   

   • When true, the authentication header is sent with Authorization-bin key using binary marshaller.

   • When false, the authentication header is sent with Authorization key using ASCII marshaller.

4. Provide token generator function (Please refer to for example.)

Per-call

class MyClient{
    public void doWork(){
        AuthCallCredentials callCredentials = new AuthCallCredentials( (1)
                AuthHeader.builder().basic("user","pwd".getBytes())
        );

        final SecuredGreeterGrpc.SecuredGreeterBlockingStub securedFutureStub = SecuredGreeterGrpc.newBlockingStub(ManagedChannelBuilder.forAddress("host", 6565));(2)

        final String reply = securedFutureStub
                .withCallCredentials(callCredentials)(3)
                .sayAuthHello(Empty.getDefaultInstance()).getMessage();

    }
 }

1. Create call credentials with basic scheme

2. Create service stub

3. Attach call credentials to the call

   AuthHeader could also be built with bespoke authorization scheme :

    AuthHeader
      .builder()
      .authScheme("myCustomAuthScheme")
      .tokenSupplier(()->generateMyCustomToken())

11. Health check

The starter registers the default implementation of HealthServiceImpl.
You can provide you own by registering ManagedHealthStatusService bean in your application context.

12. Spring actuator support

If you have org.springframework.boot:spring-boot-starter-actuator and org.springframework.boot:spring-boot-starter-web in the classpath, the starter will expose:

• grpc health indicator under /actuator/health endpoint.

• /actuator/grpc endpoint.

This can be controlled by standard endpoints and health configuration.

13. Consul Integration

Starting from version 3.3.0, the starter will auto-register the running grpc server in Consul registry if org.springframework.cloud:spring-cloud-starter-consul-discovery is in classpath and spring.cloud.service-registry.auto-registration.enabled is NOT set to false.

The registered service name will be prefixed with grpc- ,i.e. grpc-${spring.application.name} to not interfere with standard registered web-service name if you choose to run both embedded Grpc and Web servers.

ConsulDiscoveryProperties are bound from configuration properties prefixed by spring.cloud.consul.discovery and then the values are overwritten by grpc.consul.discovery prefixed properties (if set). This allows you to have separate consul discovery configuration for rest and grpc services if you choose to expose both from your application.

spring:
  cloud:
    consul:
      discovery:
        metadata:
          myKey: myValue (1)
        tags:
          - myWebTag (2)
grpc:
  consul:
    discovery:
      tags:
        - myGrpcTag (3)

1. Both rest and grpc services are registered with metadata myKey=myValue

2. Rest services are registered with myWebTag

3. Grpc services are registered with myGrpcTag

Setting spring.cloud.consul.discovery.register-health-check (or grpc.consul.discovery.register-health-check) to true will register GRPC health check service with Consul.

There are 4 supported registration modes :

1. SINGLE_SERVER_WITH_GLOBAL_CHECK (default)
   In this mode the running grpc server is registered as single service with single grpc check with empty serviceId.
   Please note that default implementation does nothing and simply returns SERVING status. You might want to provide your custom Health check implementation for this mode.

2. SINGLE_SERVER_WITH_CHECK_PER_SERVICE
   In this mode the running grpc server is registered as single service with check per each discovered grpc service.

3. STANDALONE_SERVICES
   In this mode each discovered grpc service is registered as single service with single check. Each registered service is tagged by its own service name.

4. NOOP - no grpc services registered. This mode is useful if you serve both rest and grpc services in your application, but for some reason, only rest services should be registered with Consul.

You can control the desired mode from application.properties

grpc:
  consule:
    registration-mode: SINGLE_SERVER_WITH_CHECK_PER_SERVICE

14. Eureka Integration

When building production-ready services, the advise is to have separate project for your service(s) gRPC API that holds only proto-generated classes both for server and client side usage.
You will then add this project as implementation dependency to your gRPC client and gRPC server projects.

To integrate Eureka simply follow the great guide from Spring.

Below are the essential parts of configurations for both server and client projects.

14.1. gRPC Server Project

• Add eureka starter as dependency of your server project together with generated classes from proto files:

build.gradle

 dependencies {
     implementation('org.springframework.cloud:spring-cloud-starter-eureka')
     implementation project(":yourProject-api")
 }

• Configure gRPC server to register itself with Eureka.

  bootstrap.yaml

  spring:
      application:
          name: my-service-name (1)

  1. Eureka’s ServiceId by default is the spring application name, provide it before the service registers itself with Eureka.

     application.yaml

     grpc:
         port: 6565 (1)
     eureka:
         instance:
             nonSecurePort: ${grpc.port} (2)
         client:
             serviceUrl:
                 defaultZone: http://${eureka.host:localhost}:${eureka.port:8761}/eureka/ (3)

  2. Specify the port number the gRPC is listening on.

  3. Register the eureka service port to be the same as grpc.port so client will know where to send the requests to.

  4. Specify the registry URL, so the service will register itself with.

• Expose the gRPC service as part of Spring Boot Application.

  EurekaGrpcServiceApp.java

   @SpringBootApplication
   @EnableEurekaClient
   public class EurekaGrpcServiceApp {
  
       @GRpcService
       public static class GreeterService extends GreeterGrpc.GreeterImplBase {
           @Override
           public void sayHello(GreeterOuterClass.HelloRequest request, StreamObserver<GreeterOuterClass.HelloReply> responseObserver) {
  
           }
       }
  
       public static void main(String[] args) {
           SpringApplication.run(DemoApp.class,args);
       }
   }

14.2. gRPC Client Project

• Add eureka starter as dependency of your client project together with generated classes from proto files:

build.gradle

 dependencies {
     implementation('org.springframework.cloud:spring-cloud-starter-eureka')
     implementation project(":yourProject-api")
 }

• Configure client to find the eureka service registry:

application.yaml

eureka:
  client:
    register-with-eureka: false (1)
    service-url:
      defaultZone: http://${eureka.host:localhost}:${eureka.port:8761}/eureka/ (2)

1. false if this project is not meant to act as a service to another client.

2. Specify the registry URL, so this client will know where to look up the required service.

GreeterServiceConsumerApplication.java

@EnableEurekaClient
@SpringBootApplication
public class GreeterServiceConsumerApplication {
 public static void main(String[] args) {
   SpringApplication.run(GreeterServiceConsumerApplication.class, args);
 }
}

• Use EurekaClient to get the coordinates of gRPC service instance from Eureka and consume the service :

GreeterServiceConsumer.java

@EnableEurekaClient
@Component
public class GreeterServiceConsumer {
    @Autowired
    private EurekaClient client;

    public void greet(String name) {
        final InstanceInfo instanceInfo = client.getNextServerFromEureka("my-service-name", false);//(1)
        final ManagedChannel channel = ManagedChannelBuilder.forAddress(instanceInfo.getIPAddr(), instanceInfo.getPort())
                .usePlaintext()
                .build(); //(2)
        final GreeterServiceGrpc.GreeterServiceFutureStub stub = GreeterServiceGrpc.newFutureStub(channel); //(3)
        stub.greet(name); //(4)

    }
}

1. Get the information about the my-service-name instance.

2. Build channel accordingly.

3. Create stub using the channel.

4. Invoke the service.

15. License

Apache 2.0