@Override
    protected IMetrics createMetrics(IPluginRegistry pluginRegistry) {
        return new InMemoryMetrics();
    }
@see io.apiman.gateway.engine.impl.AbstractEngineFactory#createMetrics(io.apiman.gateway.engine.IPluginRegistry)
gateway/engine/core/src/main/java/io/apiman/gateway/engine/impl/DefaultEngineFactory.java