public List<Snapshot> readSnapshots() {
        List<Snapshot> snapshots = new ArrayList<>();
        for (var hostname : db.getChildren(snapshotsPath)) {
            snapshots.addAll(readSnapshots(hostname));
        }
        return snapshots;
    }
Returns the instant after which a firmware check is required, if any.
node-repository/src/main/java/com/yahoo/vespa/hosted/provision/persistence/CuratorDb.java