public Set<ConfigKey<? extends ConfigInstance>> configKeys() {
        return nodes().stream().flatMap(node -> node.configKeys().stream()).collect(Collectors.toSet());
    }
@author Tony Vaagenes
@author gjoranv
@author ollivir

Not thread safe.
container-core/src/main/java/com/yahoo/container/di/componentgraph/core/ComponentGraph.java