gRPC

Since Camel 2.19

Both producer and consumer are supported

The gRPC component allows you to call or expose Remote Procedure Call (RPC) services using Protocol Buffers (protobuf) exchange format over HTTP/2 transport.

Maven users will need to add the following dependency to their pom.xml for this component:

<dependency>
    <groupId>org.apache.camel</groupId>
    <artifactId>camel-grpc</artifactId>
    <version>x.x.x</version>
    <!-- use the same version as your Camel core version -->
</dependency>

URI format

grpc:host:port/service[?options]

Configuring Options

Camel components are configured on two separate levels:

  • component level

  • endpoint level

Configuring Component Options

The component level is the highest level which holds general and common configurations that are inherited by the endpoints. For example a component may have security settings, credentials for authentication, urls for network connection and so forth.

Some components only have a few options, and others may have many. Because components typically have pre configured defaults that are commonly used, then you may often only need to configure a few options on a component; or none at all.

Configuring components can be done with the Component DSL, in a configuration file (application.properties|yaml), or directly with Java code.

Configuring Endpoint Options

Where you find yourself configuring the most is on endpoints, as endpoints often have many options, which allows you to configure what you need the endpoint to do. The options are also categorized into whether the endpoint is used as consumer (from) or as a producer (to), or used for both.

Configuring endpoints is most often done directly in the endpoint URI as path and query parameters. You can also use the Endpoint DSL and DataFormat DSL as a type safe way of configuring endpoints and data formats in Java.

A good practice when configuring options is to use Property Placeholders, which allows to not hardcode urls, port numbers, sensitive information, and other settings. In other words placeholders allows to externalize the configuration from your code, and gives more flexibility and reuse.

The following two sections lists all the options, firstly for the component followed by the endpoint.

Component Options

The gRPC component supports 3 options, which are listed below.

Name Description Default Type

bridgeErrorHandler (consumer)

Allows for bridging the consumer to the Camel routing Error Handler, which mean any exceptions (if possible) occurred while the Camel consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. Important: This is only possible if the 3rd party component allows Camel to be alerted if an exception was thrown. Some components handle this internally only, and therefore bridgeErrorHandler is not possible. In other situations we may improve the Camel component to hook into the 3rd party component and make this possible for future releases. By default the consumer will use the org.apache.camel.spi.ExceptionHandler to deal with exceptions, that will be logged at WARN or ERROR level and ignored.

false

boolean

lazyStartProducer (producer)

Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel’s routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing.

false

boolean

autowiredEnabled (advanced)

Whether autowiring is enabled. This is used for automatic autowiring options (the option must be marked as autowired) by looking up in the registry to find if there is a single instance of matching type, which then gets configured on the component. This can be used for automatic configuring JDBC data sources, JMS connection factories, AWS Clients, etc.

true

boolean

Endpoint Options

The gRPC endpoint is configured using URI syntax:

grpc:host:port/service

with the following path and query parameters:

Path Parameters (3 parameters)

Name Description Default Type

host (common)

Required The gRPC server host name. This is localhost or 0.0.0.0 when being a consumer or remote server host name when using producer.

String

port (common)

Required The gRPC local or remote server port.

int

service (common)

Required Fully qualified service name from the protocol buffer descriptor file (package dot service definition name).

String

Query Parameters (31 parameters)

Name Description Default Type

flowControlWindow (common)

The HTTP/2 flow control window size (MiB).

1048576

int

maxMessageSize (common)

The maximum message size allowed to be received/sent (MiB).

4194304

int

autoDiscoverServerInterceptors (consumer)

Setting the autoDiscoverServerInterceptors mechanism, if true, the component will look for a ServerInterceptor instance in the registry automatically otherwise it will skip that checking.

true

boolean

consumerStrategy (consumer)

This option specifies the top-level strategy for processing service requests and responses in streaming mode. If an aggregation strategy is selected, all requests will be accumulated in the list, then transferred to the flow, and the accumulated responses will be sent to the sender. If a propagation strategy is selected, request is sent to the stream, and the response will be immediately sent back to the sender. If a delegation strategy is selected, request is sent to the stream, but no response generated under the assumption that all necessary responses will be sent at another part of route. Delegation strategy always comes with routeControlledStreamObserver=true to be able to achieve the assumption.

Enum values:

  • AGGREGATION

  • PROPAGATION

  • DELEGATION

PROPAGATION

GrpcConsumerStrategy

forwardOnCompleted (consumer)

Determines if onCompleted events should be pushed to the Camel route.

false

boolean

forwardOnError (consumer)

Determines if onError events should be pushed to the Camel route. Exceptions will be set as message body.

false

boolean

maxConcurrentCallsPerConnection (consumer)

The maximum number of concurrent calls permitted for each incoming server connection.

2147483647

int

routeControlledStreamObserver (consumer)

Lets the route to take control over stream observer. If this value is set to true, then the response observer of gRPC call will be set with the name GrpcConstants.GRPC_RESPONSE_OBSERVER in the Exchange object. Please note that the stream observer’s onNext(), onError(), onCompleted() methods should be called in the route.

false

boolean

bridgeErrorHandler (consumer (advanced))

Allows for bridging the consumer to the Camel routing Error Handler, which mean any exceptions (if possible) occurred while the Camel consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. Important: This is only possible if the 3rd party component allows Camel to be alerted if an exception was thrown. Some components handle this internally only, and therefore bridgeErrorHandler is not possible. In other situations we may improve the Camel component to hook into the 3rd party component and make this possible for future releases. By default the consumer will use the org.apache.camel.spi.ExceptionHandler to deal with exceptions, that will be logged at WARN or ERROR level and ignored.

false

boolean

exceptionHandler (consumer (advanced))

To let the consumer use a custom ExceptionHandler. Notice if the option bridgeErrorHandler is enabled then this option is not in use. By default the consumer will deal with exceptions, that will be logged at WARN or ERROR level and ignored.

ExceptionHandler

exchangePattern (consumer (advanced))

Sets the exchange pattern when the consumer creates an exchange.

Enum values:

  • InOnly

  • InOut

ExchangePattern

autoDiscoverClientInterceptors (producer)

Setting the autoDiscoverClientInterceptors mechanism, if true, the component will look for a ClientInterceptor instance in the registry automatically otherwise it will skip that checking.

true

boolean

inheritExchangePropertiesForReplies (producer)

Copies exchange properties from original exchange to all exchanges created for route defined by streamRepliesTo.

false

boolean

method (producer)

gRPC method name.

String

producerStrategy (producer)

The mode used to communicate with a remote gRPC server. In SIMPLE mode a single exchange is translated into a remote procedure call. In STREAMING mode all exchanges will be sent within the same request (input and output of the recipient gRPC service must be of type 'stream').

Enum values:

  • SIMPLE

  • STREAMING

SIMPLE

GrpcProducerStrategy

streamRepliesTo (producer)

When using STREAMING client mode, it indicates the endpoint where responses should be forwarded.

String

toRouteControlledStreamObserver (producer)

Expects that exchange property GrpcConstants.GRPC_RESPONSE_OBSERVER is set. Takes its value and calls onNext, onError and onComplete on that StreamObserver. All other gRPC parameters are ignored.

false

boolean

userAgent (producer)

The user agent header passed to the server.

String

lazyStartProducer (producer (advanced))

Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel’s routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing.

false

boolean

synchronous (advanced)

Sets whether synchronous processing should be strictly used.

false

boolean

authenticationType (security)

Authentication method type in advance to the SSL/TLS negotiation.

Enum values:

  • NONE

  • GOOGLE

  • JWT

NONE

GrpcAuthType

jwtAlgorithm (security)

JSON Web Token sign algorithm.

Enum values:

  • HMAC256

  • HMAC384

  • HMAC512

HMAC256

JwtAlgorithm

jwtIssuer (security)

JSON Web Token issuer.

String

jwtSecret (security)

JSON Web Token secret.

String

jwtSubject (security)

JSON Web Token subject.

String

keyCertChainResource (security)

The X.509 certificate chain file resource in PEM format link.

String

keyPassword (security)

The PKCS#8 private key file password.

String

keyResource (security)

The PKCS#8 private key file resource in PEM format link.

String

negotiationType (security)

Identifies the security negotiation type used for HTTP/2 communication.

Enum values:

  • TLS

  • PLAINTEXT_UPGRADE

  • PLAINTEXT

PLAINTEXT

NegotiationType

serviceAccountResource (security)

Service Account key file in JSON format resource link supported by the Google Cloud SDK.

String

trustCertCollectionResource (security)

The trusted certificates collection file resource in PEM format for verifying the remote endpoint’s certificate.

String

Message Headers

The gRPC component supports 3 message header(s), which is/are listed below:

Name Description Default Type

CamelGrpcMethodName (consumer)

Constant: GRPC_METHOD_NAME_HEADER

Method name handled by the consumer service.

String

CamelGrpcUserAgent (consumer)

Constant: GRPC_USER_AGENT_HEADER

If provided, the given agent will prepend the gRPC library’s user agent information.

String

CamelGrpcEventType (consumer)

Constant: GRPC_EVENT_TYPE_HEADER

Received event type from the sent request. Possible values: onNext onCompleted onError.

String

Transport security and authentication support

The following authentication mechanisms are built-in to gRPC and available in this component:

  • SSL/TLS: gRPC has SSL/TLS integration and promotes the use of SSL/TLS to authenticate the server, and to encrypt all the data exchanged between the client and the server. Optional mechanisms are available for clients to provide certificates for mutual authentication.

  • Token-based authentication with Google: gRPC provides a generic mechanism to attach metadata based credentials to requests and responses. Additional support for acquiring access tokens while accessing Google APIs through gRPC is provided. In general this mechanism must be used as well as SSL/TLS on the channel.

To enable these features the following component properties combinations must be configured:

Num. Option Parameter Value Required/Optional

1

SSL/TLS

negotiationType

TLS

Required

keyCertChainResource

Required

keyResource

Required

keyPassword

Optional

trustCertCollectionResource

Optional

2

Token-based authentication with Google API

authenticationType

GOOGLE

Required

negotiationType

TLS

Required

serviceAccountResource

Required

3

Custom JSON Web Token implementation authentication

authenticationType

JWT

Required

negotiationType

NONE or TLS

Optional. The TLS/SSL not checking for this type, but strongly recommended.

jwtAlgorithm

HMAC256(default) or (HMAC384,HMAC512)

Optional

jwtSecret

Required

jwtIssuer

Optional

jwtSubject

Optional

gRPC producer resource type mapping

The table below shows the types of objects in the message body, depending on the types (simple or stream) of incoming and outgoing parameters, as well as the invocation style (synchronous or asynchronous). Please note, that invocation of the procedures with incoming stream parameter in asynchronous style are not allowed.

Invocation style Request type Response type Request Body Type Result Body Type

synchronous

simple

simple

Object

Object

synchronous

simple

stream

Object

List<Object>

synchronous

stream

simple

not allowed

not allowed

synchronous

stream

stream

not allowed

not allowed

asynchronous

simple

simple

Object

List<Object>

asynchronous

simple

stream

Object

List<Object>

asynchronous

stream

simple

Object or List<Object>

List<Object>

asynchronous

stream

stream

Object or List<Object>

List<Object>

gRPC Proxy

It is not possible to create universal proxy-route for all methods, so you need to divide your gRPC service into several services by method’s type: unary, server streaming, client streaming and bidirectional streaming.

Unary

For unary requests it is enough to write the following code:

from("grpc://localhost:1101" +
    "/org.apache.camel.component.grpc.PingPong"
)
    .toD("grpc://remotehost:1101" +
        "/org.apache.camel.component.grpc.PingPong" +
        "?method=${header.CamelGrpcMethodName}"
    )

Server streaming

Server streaming may be done by the same approach as unary, but in that configuration Camel route will wait stream for completion and will aggregate all responses to list before sending that data as response stream. If this behavior is unacceptable, you need to apply a number of options:

  1. Set routeControlledStreamObserver=true for consumer. Later it will be used to publish responses;

  2. Set streamRepliesTo option for producer to handle streaming nature of responses;

  3. Set forwarding of onError and onCompleted for producer;

  4. Set inheritExchangePropertiesForReplies=true to inherit StreamObserver obtained on the first step;

  5. Create another route to process streamed data. That route must contain gRPC-producer step with the only parameter toRouteControlledStreamObserver=true which will publish incoming exchanges as response stream elements.

Example:

from("grpc://localhost:1101" +
    "/org.apache.camel.component.grpc.PingPong" +
    "?routeControlledStreamObserver=true"
)
    .toD("grpc://remotehost:1101" +
            "/org.apache.camel.component.grpc.PingPong" +
            "?method=${header.CamelGrpcMethodName}" +
            "&streamRepliesTo=direct:next" +
            "&forwardOnError=true" +
            "&forwardOnCompleted=true" +
            "&inheritExchangePropertiesForReplies=true"
    );

from("direct:next")
        .to("grpc://dummy:0/?toRouteControlledStreamObserver=true");

Client streaming and bidirectional streaming

Both client streaming and bidirectional streaming gRPC methods exposes StreamObserver as responses handler, so you need the same technic as described in server streaming section — all 5 steps.

But there another thing — requests also comes in streaming mode. So you need the following:

  1. Set consumer strategy to DELEGATION — that differs from default PROPAGATION option in the fact that consumer will not produce responses at all. If you set PROPAGATION, then you will receive more responses than you expected;

  2. Forward onError and onCompletion on consumer;

  3. Set producer strategy to STREAMING.

Example:

from("grpc://localhost:1101" +
    "/org.apache.camel.component.grpc.PingPong" +
    "?routeControlledStreamObserver=true" +
    "&consumerStrategy=DELEGATION" +
    "&forwardOnError=true" +
    "&forwardOnCompleted=true"
)
    .toD("grpc://remotehost:1101" +
            "/org.apache.camel.component.grpc.PingPong" +
            "?method=${header.CamelGrpcMethodName}" +
            "&producerStrategy=STREAMING" +
            "&streamRepliesTo=direct:next" +
            "&forwardOnError=true" +
            "&forwardOnCompleted=true" +
            "&inheritExchangePropertiesForReplies=true"
    );

from("direct:next")
        .to("grpc://dummy:0/?toRouteControlledStreamObserver=true");

Examples

Below is a simple synchronous method invoke with host and port parameters

from("direct:grpc-sync")
.to("grpc://remotehost:1101/org.apache.camel.component.grpc.PingPong?method=sendPing&synchronous=true");
<route>
    <from uri="direct:grpc-sync" />
    <to uri="grpc://remotehost:1101/org.apache.camel.component.grpc.PingPong?method=sendPing&synchronous=true"/>
</route>

An asynchronous method invoke

from("direct:grpc-async")
.to("grpc://remotehost:1101/org.apache.camel.component.grpc.PingPong?method=pingAsyncResponse");

gRPC service consumer with propagation consumer strategy

from("grpc://localhost:1101/org.apache.camel.component.grpc.PingPong?consumerStrategy=PROPAGATION")
.to("direct:grpc-service");

gRPC service producer with streaming producer strategy (requires a service that uses "stream" mode as input and output)

from("direct:grpc-request-stream")
.to("grpc://remotehost:1101/org.apache.camel.component.grpc.PingPong?method=PingAsyncAsync&producerStrategy=STREAMING&streamRepliesTo=direct:grpc-response-stream");

from("direct:grpc-response-stream")
.log("Response received: ${body}");

gRPC service consumer TLS/SSL security negotiation enabled

from("grpc://localhost:1101/org.apache.camel.component.grpc.PingPong?consumerStrategy=PROPAGATION&negotiationType=TLS&keyCertChainResource=file:src/test/resources/certs/server.pem&keyResource=file:src/test/resources/certs/server.key&trustCertCollectionResource=file:src/test/resources/certs/ca.pem")
.to("direct:tls-enable")

gRPC service producer with custom JSON Web Token (JWT) implementation authentication

from("direct:grpc-jwt")
.to("grpc://localhost:1101/org.apache.camel.component.grpc.PingPong?method=pingSyncSync&synchronous=true&authenticationType=JWT&jwtSecret=supersecuredsecret");

Configuration

It is recommended to use the protobuf-maven-plugin, which calls the Protocol Buffer Compiler (protoc) to generate Java source files from .proto (protocol buffer definition) files. This plugin will generate procedures request and response classes, their builders and gRPC procedures stubs classes as well.

Following steps are required:

Insert operating system and CPU architecture detection extension inside <build> tag of the project pom.xml or set ${os.detected.classifier} parameter manually

<extensions>
  <extension>
    <groupId>kr.motd.maven</groupId>
    <artifactId>os-maven-plugin</artifactId>
    <version>1.7.1</version>
  </extension>
</extensions>

Insert the gRPC and protobuf Java code generator plugins into the <plugins> tag of the project pom.xml

<plugin>
  <groupId>org.xolstice.maven.plugins</groupId>
  <artifactId>protobuf-maven-plugin</artifactId>
  <version>0.6.1</version>
  <configuration>
    <protocArtifact>com.google.protobuf:protoc:${protobuf-version}:exe:${os.detected.classifier}</protocArtifact>
    <pluginId>grpc-java</pluginId>
    <pluginArtifact>io.grpc:protoc-gen-grpc-java:${grpc-version}:exe:${os.detected.classifier}</pluginArtifact>
  </configuration>
  <executions>
    <execution>
      <goals>
        <goal>compile</goal>
        <goal>compile-custom</goal>
        <goal>test-compile</goal>
        <goal>test-compile-custom</goal>
      </goals>
    </execution>
  </executions>
</plugin>

More information

See these resources: