private BrokerRegistration getBrokerOrThrow(int brokerId, long epoch, String action) {
        BrokerRegistration broker = broker(brokerId);
        if (broker == null) {
            throw new IllegalStateException("Tried to " + action + " broker " + brokerId +
                ", but that broker was not registered.");
        }
        if (broker.epoch() != epoch) {
            throw new IllegalStateException("Tried to " + action + " broker " + brokerId +
                ", but the given epoch, " + epoch + ", did not match the current broker " +
                "epoch, " + broker.epoch());
        }
        return broker;
    }
Represents changes to the cluster in the metadata image.
metadata/src/main/java/org/apache/kafka/image/ClusterDelta.java