String allocationFailureDetails() {
        List<String> reasons = new ArrayList<>();
        if (rejectedDueToExclusivity > 0)
            reasons.add("host exclusivity constraints");
        if (rejectedDueToClashingParentHost > 0)
            reasons.add("insufficient nodes available on separate physical hosts");
        if (wasRetiredJustNow > 0)
            reasons.add("retirement of allocated nodes");
        if (rejectedDueToInsufficientRealResources > 0)
            reasons.add("insufficient real resources on hosts");

        if (reasons.isEmpty()) return "";
        return ": Not enough suitable nodes available due to " + String.join(", ", reasons);
    }
Returns the number of nodes accepted this far
node-repository/src/main/java/com/yahoo/vespa/hosted/provision/provisioning/NodeAllocation.java