Google Pubsub

Since Camel 2.19

Both producer and consumer are supported

The Google Pubsub component provides access to Cloud Pub/Sub Infrastructure via the Google Cloud Java Client for Google Cloud Pub/Sub.

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

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

URI Format

The Google Pubsub Component uses the following URI format:

google-pubsub://project-id:destinationName?[options]

Destination Name can be either a topic or a subscription name.

Configuring Options

Camel components are configured on two separate levels:

  • component level

  • endpoint level

Configuring Component Options

At the component level, you set general and shared configurations that are, then, inherited by the endpoints. It is the highest configuration level.

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.

You can configure components using:

  • the Component DSL.

  • in a configuration file (application.properties, *.yaml files, etc).

  • directly in the Java code.

Configuring Endpoint Options

You usually spend more time setting up endpoints because they have many options. These options help you customize what you want the endpoint to do. The options are also categorized into whether the endpoint is used as a consumer (from), as a producer (to), or 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.

Property placeholders provide a few benefits:

  • They help prevent using hardcoded urls, port numbers, sensitive information, and other settings.

  • They allow externalizing the configuration from the code.

  • They help the code to become more flexible and reusable.

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

Component Options

The Google Pubsub component supports 10 options, which are listed below.

Name Description Default Type

authenticate (common)

Use Credentials when interacting with PubSub service (no authentication is required when using emulator).

true

boolean

endpoint (common)

Endpoint to use with local Pub/Sub emulator.

String

serviceAccountKey (common)

The Service account key that can be used as credentials for the PubSub publisher/subscriber. It can be loaded by default from classpath, but you can prefix with classpath:, file:, or http: to load the resource from different systems.

String

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

synchronousPullRetryableCodes (consumer)

Comma-separated list of additional retryable error codes for synchronous pull. By default the PubSub client library retries ABORTED, UNAVAILABLE, UNKNOWN.

String

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

publisherCacheSize (producer)

Maximum number of producers to cache. This could be increased if you have producers for lots of different topics.

int

publisherCacheTimeout (producer)

How many milliseconds should each producer stay alive in the cache.

int

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

publisherTerminationTimeout (advanced)

How many milliseconds should a producer be allowed to terminate.

int

Endpoint Options

The Google Pubsub endpoint is configured using URI syntax:

google-pubsub:projectId:destinationName

With the following path and query parameters:

Path Parameters (2 parameters)

Name Description Default Type

projectId (common)

Required The Google Cloud PubSub Project Id.

String

destinationName (common)

Required The Destination Name. For the consumer this will be the subscription name, while for the producer this will be the topic name.

String

Query Parameters (16 parameters)

Name Description Default Type

authenticate (common)

Use Credentials when interacting with PubSub service (no authentication is required when using emulator).

true

boolean

loggerId (common)

Logger ID to use when a match to the parent route required.

String

serviceAccountKey (common)

The Service account key that can be used as credentials for the PubSub publisher/subscriber. It can be loaded by default from classpath, but you can prefix with classpath:, file:, or http: to load the resource from different systems.

String

ackMode (consumer)

AUTO = exchange gets ack’ed/nack’ed on completion. NONE = downstream process has to ack/nack explicitly.

Enum values:

  • AUTO

  • NONE

AUTO

AckMode

concurrentConsumers (consumer)

The number of parallel streams consuming from the subscription.

1

Integer

maxAckExtensionPeriod (consumer)

Set the maximum period a message ack deadline will be extended. Value in seconds.

3600

int

maxMessagesPerPoll (consumer)

The max number of messages to receive from the server in a single API call.

1

Integer

synchronousPull (consumer)

Synchronously pull batches of messages.

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

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

messageOrderingEnabled (producer (advanced))

Should message ordering be enabled.

false

boolean

pubsubEndpoint (producer (advanced))

Pub/Sub endpoint to use. Required when using message ordering, and ensures that messages are received in order even when multiple publishers are used.

String

retry (producer (advanced))

A custom RetrySettings to control how the publisher handles retry-able failures.

RetrySettings

serializer (producer (advanced))

Autowired A custom GooglePubsubSerializer to use for serializing message payloads in the producer.

GooglePubsubSerializer

Message Headers

The Google Pubsub component supports 6 message header(s), which is/are listed below:

Name Description Default Type

CamelGooglePubsubMessageId (common)

Constant: MESSAGE_ID

The ID of the message, assigned by the server when the message is published.

String

CamelGooglePubsubMsgAckId (consumer)

Constant: ACK_ID

The ID used to acknowledge the received message.

String

CamelGooglePubsubPublishTime (consumer)

Constant: PUBLISH_TIME

The time at which the message was published.

Timestamp

CamelGooglePubsubAttributes (common)

Constant: ATTRIBUTES

The attributes of the message.

Map

CamelGooglePubsubOrderingKey (producer)

Constant: ORDERING_KEY

If non-empty, identifies related messages for which publish order should be respected.

String

CamelGooglePubsubAcknowledge (consumer)

Constant: GOOGLE_PUBSUB_ACKNOWLEDGE

Can be used to manually acknowledge or negative-acknowledge a message when ackMode=NONE.

GooglePubsubAcknowledge

Usage

Producer Endpoints

Producer endpoints can accept and deliver to PubSub individual and grouped exchanges alike. Grouped exchanges have Exchange.GROUPED_EXCHANGE property set.

Google PubSub expects the payload to be byte[] array, Producer endpoints will send:

  • String body as byte[] encoded as UTF-8

  • byte[] body as is

  • Everything else will be serialised into a byte[] array

A Map set as message header GooglePubsubConstants.ATTRIBUTES will be sent as PubSub attributes.

Google PubSub supports ordered message delivery.

To enable this, set the options messageOrderingEnabled to true, and the pubsubEndpoint to a GCP region.

When producing messages set the message header GooglePubsubConstants.ORDERING_KEY . This will be set as the PubSub orderingKey for the message.

For more information, see Ordering messages.

Once exchange has been delivered to PubSub the PubSub Message ID will be assigned to the header GooglePubsubConstants.MESSAGE_ID.

Consumer Endpoints

Google PubSub will redeliver the message if it has not been acknowledged within the time period set as a configuration option on the subscription.

The component will acknowledge the message once exchange processing has been completed.

If the route throws an exception, the exchange is marked as failed, and the component will NACK the message. It will be redelivered immediately.

To ack/nack the message the component uses Acknowledgement ID stored as header GooglePubsubConstants.ACK_ID. If the header is removed or tampered with, the ack will fail and the message will be redelivered again after the ack deadline.

Message Body

The consumer endpoint returns the content of the message as byte[]. Exactly as the underlying system sends it. It is up for the route to convert/unmarshall the contents.

Authentication Configuration

By default, this component acquires credentials using GoogleCredentials.getApplicationDefault(). This behavior can be disabled by setting authenticate option to false, in which case requests to Google API will be made without authentication details. This is only desirable when developing against an emulator. This behavior can be altered by supplying a path to a service account key file.

Rollback and Redelivery

The rollback for Google PubSub relies on the idea of the Acknowledgement Deadline - the time period where Google PubSub expects to receive the acknowledgement. If the acknowledgement has not been received, the message is redelivered.

Google provides an API to extend the deadline for a message.

More information in Google PubSub Documentation

So, rollback is effectively a deadline extension API call with zero value - i.e., deadline is reached now, and the message can be redelivered to the next consumer.

It is possible to delay the message redelivery by setting the acknowledgement deadline explicitly for the rollback by setting the message header GooglePubsubConstants.ACK_DEADLINE to the value in seconds.

Spring Boot Auto-Configuration

When using google-pubsub with Spring Boot make sure to use the following Maven dependency to have support for auto configuration:

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

The component supports 11 options, which are listed below.

Name Description Default Type

camel.component.google-pubsub.authenticate

Use Credentials when interacting with PubSub service (no authentication is required when using emulator).

true

Boolean

camel.component.google-pubsub.autowired-enabled

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

camel.component.google-pubsub.bridge-error-handler

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

camel.component.google-pubsub.enabled

Whether to enable auto configuration of the google-pubsub component. This is enabled by default.

Boolean

camel.component.google-pubsub.endpoint

Endpoint to use with local Pub/Sub emulator.

String

camel.component.google-pubsub.lazy-start-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

camel.component.google-pubsub.publisher-cache-size

Maximum number of producers to cache. This could be increased if you have producers for lots of different topics.

Integer

camel.component.google-pubsub.publisher-cache-timeout

How many milliseconds should each producer stay alive in the cache.

Integer

camel.component.google-pubsub.publisher-termination-timeout

How many milliseconds should a producer be allowed to terminate.

Integer

camel.component.google-pubsub.service-account-key

The Service account key that can be used as credentials for the PubSub publisher/subscriber. It can be loaded by default from classpath, but you can prefix with classpath:, file:, or http: to load the resource from different systems.

String

camel.component.google-pubsub.synchronous-pull-retryable-codes

Comma-separated list of additional retryable error codes for synchronous pull. By default the PubSub client library retries ABORTED, UNAVAILABLE, UNKNOWN.

String

Manual Acknowledgement

By default, the PubSub consumer will acknowledge messages once the exchange has been processed, or negative-acknowledge them if the exchange has failed.

If the ackMode option is set to NONE, the component will not acknowledge messages, and it is up to the route to do so. In this case, a GooglePubsubAcknowledge object is stored in the header GooglePubsubConstants.GOOGLE_PUBSUB_ACKNOWLEDGE and can be used to acknowledge messages:

from("google-pubsub:{{project.name}}:{{subscription.name}}?ackMode=NONE")
    .process(exchange -> {
        GooglePubsubAcknowledge acknowledge = exchange.getIn().getHeader(GooglePubsubConstants.GOOGLE_PUBSUB_ACKNOWLEDGE, GooglePubsubAcknowledge.class);
        acknowledge.ack(exchange); // or .nack(exchange)
    });

Manual acknowledgement works with both the asynchronous and synchronous consumers and will use the acknowledgement id which is stored in GooglePubsubConstants.ACK_ID.

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