public Set<Version> availableTo(Node host, Version requestedVersion) {
        if (hostProvisioner.isEmpty()) {
            return Set.of(requestedVersion);
        }
        try {
            return availableVersions.get(host.cloudAccount(),
                                         () -> hostProvisioner.get().osVersions(host, requestedVersion.getMajor()));
        } catch (ExecutionException e) {
            LOG.log(Level.WARNING, "Failed to list supported OS versions in " + host.cloudAccount() + ": " + Exceptions.toMessageString(e));
            return Set.of();
        }
    }
Returns the versions available to given host
node-repository/src/main/java/com/yahoo/vespa/hosted/provision/os/OsVersions.java