@Override
    public boolean equals(Object o) {
        if (!(o instanceof UsableBroker)) return false;
        UsableBroker other = (UsableBroker) o;
        return other.id == id && other.rack.equals(rack) && other.fenced == fenced;
    }
A broker where a replica can be placed.
metadata/src/main/java/org/apache/kafka/metadata/placement/UsableBroker.java