code: public OvhInterface project_serviceName_instance_instanceId_interface_POST(String serviceName, String instanceId, String ip, String networkId) throws IOException {
  		String qPath = "/cloud/project/{serviceName}/instance/{instanceId}/interface";
  		StringBuilder sb = path(qPath, serviceName, instanceId);
  		HashMap<String, Object>o = new HashMap<String, Object>();
  		addBody(o, "ip", ip);
  		addBody(o, "networkId", networkId);
  		String resp = exec(qPath, "POST", sb.toString(), o);
  		return convertTo(resp, OvhInterface.class);
  	}
docs: Create interface on an instance and attached it to a network
  
  REST: POST /cloud/project/{serviceName}/instance/{instanceId}/interface
  @param instanceId [required] Instance id
  @param ip [required] Static ip (Can only be defined for private networks)
  @param networkId [required] Network id
  @param serviceName [required] Service name