dynamic-property-configuration.adoc

Dynamic Property Configuration

Property Supplier

Decaton provides some properties for you to configure how it processes tasks. These properties don’t need to be hard-coded. Decaton lets you configure some of the properties so they can be loaded dynamically.

To externalize property, you need to implement PropertySupplier and configure it for Decaton processor.

Central Dogma Property Supplier

Central Dogma is a highly-available version-controlled service configuration repository. Decaton supports it as a property supplier out-of-the-box. If you already have a Central Dogma server, you only need to configure appropriate CentralDogmaPropertySupplier for the Decaton processor to use it.

Add the decaton-centraldogma dependency to your project. And we will use Central Dogma Java Client library to access Central Dogma here.

build.gradle

dependencies {
    implementation "com.linecorp.decaton:decaton-centraldogma:$DECATON_VERSION"
    implementation "com.linecorp.centraldogma:centraldogma-client-armeria:$CENTRALDOGMA_VERSION"
}

There are two ways to instantiate Central Dogma property supplier:

CentralDogmaPropertySupplier supplier = CentralDogmaPropertySupplier
                .register(centralDogma, PROJECT_NAME, REPOSITORY_NAME, "/properties.json"); // (1)

CentralDogmaPropertySupplier supplier = new CentralDogmaPropertySupplier(
                centralDogma, PROJECT_NAME, REPOSITORY_NAME, "/properties.json"); // (2)

1. CentralDogmaPropertySupplier.register will create a property file with default values if it doesn’t exist on Central Dogma.

2. If you already have your property file on Central Dogma, or don’t want it to be created automatically, you can instantiate it with new CentralDogmaPropertySupplier.

After creating a instance of CentralDogmaPropertySupplier, you have to configure it for Decaton processor:

CentralDogmaSupplierMain.java

ProcessorSubscription testProcessor =
        SubscriptionBuilder.newBuilder("testProcessor")
                           /* ... */
                           .properties(supplier)
                           .consumerConfig(consumerConfig)
                           .buildAndStart();

1. When you instantiate the ProcessorSubscription, use props.setBySupplier() to set your property supplier.

The following is the full example that demonstrates how to use CentralDogmaPropertySupplier:

CentralDogmaSupplierMain.java

public class CentralDogmaSupplierMain {
    public static void main(String[] args) throws Exception {
        final CentralDogma centralDogma = new ArmeriaCentralDogmaBuilder()
                .host("127.0.0.1")
                .accessToken("accesstoken")
                .build();

        CentralDogmaPropertySupplier supplier = CentralDogmaPropertySupplier
                .register(centralDogma, "project", "repository", "/testProcessor.json");

        // ...

        ProcessorSubscription testProcessor =
                SubscriptionBuilder.newBuilder("testProcessor")
                                   .processorsBuilder(
                                           ProcessorsBuilder.consuming(
                                                   "my-decaton-topic",
                                                   new ProtocolBuffersDeserializer<>(PrintMessageTask.parser()))
                                                            .thenProcess(new PrintMessageTaskProcessor())
                                   )
                                   .properties(supplier)
                                   .consumerConfig(consumerConfig)
                                   .buildAndStart();
    }
}

Multiple Property Suppliers

You can specify multiple property suppliers including one provides hardcoded properties. Suppliers are evaluated from the first to the last in given order where the first occurrence of a property for one definition is adopted. Hence you should put supplier with higher priority before others.

    .properties(
        StaticPropertySupplier.of(
            // This one is adopted even if below centralDogmaPropertySupplier contains the same property
            Property.ofStatic(ProcessorProperties.CONFIG_PARTITION_CONCURRENCY, 100),
            Property.ofStatic(...)),
        centralDogmaPropertySupplier);