Create multiple HTTP clients with same interface

Question

We need to be able to connect to multiple Elasticsearch servers. We have a simple Elasticsearch client, defined with the declarative approach of Micronaut.

However, being a multi-tenant environment, we need to be able to define many such clients. Each of these clients has obviously a different URL and needs to use a different HTTPFilter for authentication.

Micronaut being a compile-time focused framework, how can I dynamically create many such beans, defined by configuration options?

UPDATE: I see that the @Factory combined with @EachBeanannotation might be a promising way to do it, but the declarative HTTP client is an interface, not a concrete class. How can I instantiate such a client, based on the interface alone?

See https://docs.micronaut.io/latest/guide/index.html#eachBean

Answer 1

Create your declarative @Client interface normally except for 2 details :

1. make it point to a url locally "/proxy-elastic"
2. add to every declared methods a @Header("X-Elastic-Cluster") String cluster

@Client("/proxy-elastic")
public interface DeclarativeHttpClient {
    @Get("/connectors/{name}")
    void diplay(@Header(value = "X-Elastic-Cluster") String cluster, String name);
}

Then, create a ProxyFilter and mutate the HttpRequest based on the Header value (https://docs.micronaut.io/latest/guide/index.html#proxyClient)

@Filter("/proxy-elastic/**")
public class KafkaConnectClientProxy extends OncePerRequestHttpServerFilter {
    @Inject
    ProxyHttpClient client;

    @Override
    protected Publisher<MutableHttpResponse<?>> doFilterOnce(HttpRequest<?> request, ServerFilterChain chain) {
        // retrieve the config for this cluster
        String cluster = request.getHeaders().get("X-Elastic-Cluster");
        var config = getConfigForCluster(cluster);
        URI newURI = URI.create(config.url);

        // call kafka connect with proper URL and Auth
        return Publishers.map(client.proxy(
                request.mutate()
                        .uri(b -> b
                                .scheme(newURI.getScheme())
                                .host(newURI.getHost())
                                .port(newURI.getPort())
                                .replacePath(StringUtils.prependUri(
                                        newURI.getPath(),
                                        request.getPath().substring("/proxy-elastic".length())
                                ))
                        )
                        .basicAuth(config.basicAuthUsername, config.basicAuthPassword)
        ), response -> response.header("X-My-Response-Header", "YYY"));
    }
}