"use strict";
const dns = require("dns");
const utils = require("../utils");
/** @module policies/addressResolution */
/**
* Translates IP addresses received from Cassandra nodes into locally queryable
* addresses.
*
* The driver auto-detects new Cassandra nodes added to the cluster through server
* side pushed notifications and through checking the system tables. For each
* node, the address received will correspond to the address set as
* `rpc_address` in the node yaml file. In most case, this is the correct
* address to use by the driver and that is what is used by default. However,
* sometimes the addresses received through this mechanism will either not be
* reachable directly by the driver or should not be the preferred address to use
* to reach the node (for instance, the `rpc_address` set on Cassandra nodes
* might be a private IP, but some clients may have to use a public IP, or
* pass by a router to reach that node). This interface allows to deal with
* such cases, by allowing to translate an address as sent by a Cassandra node
* to another address to be used by the driver for connection.
*
* Please note that the contact points addresses provided while creating the
* {@link Client} instance are not "translated", only IP address retrieve from or sent
* by Cassandra nodes to the driver are.
*/
class AddressTranslator {
constructor() {}
/**
* Translates a Cassandra `rpc_address` to another address if necessary.
* @param {String} address the address of a node as returned by Cassandra.
*
* Note that if the `rpc_address` of a node has been configured to `0.0.0.0`
* server side, then the provided address will be the node `listen_address`,
* *not* `0.0.0.0`.
* @param {Number} port The port number, as specified in the [protocolOptions]{@link ClientOptions} at Client instance creation (9042 by default).
* @param {Function} callback Callback to invoke with endpoint as first parameter.
* The endpoint is an string composed of the IP address and the port number in the format `ipAddress:port`.
*/
translate(address, port, callback) {
callback(address + ":" + port);
}
}
/**
* {@link AddressTranslator} implementation for multi-region EC2 deployments <strong>where clients are also deployed in EC2</strong>.
*
* Its distinctive feature is that it translates addresses according to the location of the Cassandra host:
* - addresses in different EC2 regions (than the client) are unchanged
* - addresses in the same EC2 region are <strong>translated to private IPs</strong>
*
* This optimizes network costs, because Amazon charges more for communication over public IPs.
*/
class EC2MultiRegionTranslator extends AddressTranslator {
constructor() {
super();
}
/**
* Addresses in the same EC2 region are translated to private IPs and addresses in
* different EC2 regions (than the client) are unchanged
*/
translate(address, port, callback) {
let newAddress = address;
const self = this;
let name;
utils.series(
[
function resolve(next) {
dns.reverse(address, function (err, hostNames) {
if (err) {
return next(err);
}
if (!hostNames) {
return next();
}
name = hostNames[0];
next();
});
},
function lookup(next) {
if (!name) {
return next();
}
dns.lookup(name, function (err, lookupAddress) {
if (err) {
return next(err);
}
newAddress = lookupAddress;
next();
});
},
],
function (err) {
if (err) {
// there was an issue while doing dns resolution
self.logError(address, err);
}
callback(newAddress + ":" + port);
},
);
}
/**
* Log method called to log errors that occurred while performing dns resolution.
* You can assign your own method to the class instance to do proper logging.
* @param {String} address
* @param {Error} err
*/
logError(address, err) {
// Do nothing by default
}
}
exports.AddressTranslator = AddressTranslator;
exports.EC2MultiRegionTranslator = EC2MultiRegionTranslator;