public IP.Config require(String hostname) {
        IP.Config ipConfig = this.ipConfigByHostname.get(hostname);
        if (ipConfig == null) throw new IllegalArgumentException("No IP config exists for node '" + hostname + "'");
        return ipConfig;
    }
IP config of a host and its children, and an optional extra host ID.

@author mpolden
node-repository/src/main/java/com/yahoo/vespa/hosted/provision/provisioning/HostIpConfig.java