A library to retrieve your service's configuration from Consul, and subscribe to changes.
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README.md

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Consultant

Fetches your service's configuration from Consul, and subscribes to any changes.

What's Consultant?

Consultant is a Java library which allows your service to retrieve its configuration from Consul's Key/Value store. In addition to this, Consultant subscribes to any changes relevant to your service. In addition to reading the configuration from a traditional Properties object, you can also use Consultant's integration with Netflix's Governator instead.

How to use Consultant?

In order use Consultant, you'll have to create a Consultant object first. This can be done using a Builder:

Consultant consultant = Consultant.builder()
    .identifyAs("oauth")
    .build();

With the identifyAs() method you tell Consultant the identity of your service. Using this identity the correct configuration can be fetched from Consul's Key/Value store. You must at the very least specify the service's name. You can also optionally specify the name of the datacenter where the service is running, the hostname of the machine the service is running on, and instance name to describe the role of this particular instance.

Alternative you can also define this identity through environment variables:

Environment variable Corresponds to Required
SERVICE_NAME Name of the service Yes
SERVICE_DC Name of the datacenter where the service is running No
SERVICE_HOST The name of the host where this service is running on No
SERVICE_INSTANCE The name of this particular instance of the service No

Specifying an alternative Consul address

Consultant defaults Consul's REST API address to http://localhost:8500. If you wish to specify an alternative address to Consul's REST API, you can do so by using the Builder:

Consultant consultant = Consultant.builder()
    .identifyAs("oauth")
    .withConsulHost("http://some-other-host")
    .build();

Or alternatively you can also define the this through an environment variable:

Environment variable Corresponds to
CONSUL_HOST Address of Consul's REST API

Validating configurations

If you wish to impose any kind of validation on configurations (before it's exposed to your service), you can solve this using the Builder:

Consultant consultant = Consultant.builder()
    .identifyAs("oauth")
    .validateConfigWith((config) -> {
        Preconditions.checkArgument(!Strings.isNullOrEmpty(config.getProperty("database.password")));
    })
    .build();

Retrieving the configuration from Consultant

You can retrieve the current configuration from Consultant by calling the getProperties() on the Consultant class:

Consultant consultant = Consultant.builder()
    .identifyAs("oauth")
    .build();

Properties properties = consultant.getProperties();

Note that this Properties object is effectively a singleton, and is updated in-place by Consultant at run-time.

Listening for updates to the configuration

If you wish to be notified of updates to the configuration you can specify a callback in the Builder:

Consultant consultant = Consultant.builder()
    .identifyAs("oauth")
    .onValidConfig((config) -> {
        log.info("Yay, there's a new config available!");
    })
    .build();

Licensing

Consultant is available under the Apache 2 License, and is provided as is.