Neo4j High Availability Bolt Javascript Driver

_Neo4j cluster session and transparent failover_

About

This driver is a wrapper over the official Neo4j bolt driver and adds a layer of High Availability and transparent failovers

How to install

npm i --save neo4j-ha-bolt-driver

Quick example

``javascript
const servers = [
['http://127.0.0.1:7474', 'bolt://127.0.0.1:7687'],
['http://127.0.0.1:7475', 'bolt://127.0.0.1:7688']
];

const auth = { user: 'neo4j', pass: 'password' };
const strategy = Neo4jHA.HAStrategies.roundRobin;
const rwConfig = Neo4jHA.HAReadWrite.masterReadWriteSlaveRead;
const checkInterval = 500;

console.log('connecting...');
const driver = new Neo4jHA(servers, { auth, strategy, rwConfig, checkInterval }, () => {
console.log('ready');
let session;

// we get a session and we tell the driver that we will berform at least one write
// the strategy is Round Robin but because we want to write
// and the read/write config is set to masterReadWriteSlaveRead (only master can write)
// this means that it will get a session to the master
session = driver.session(true);

// don't forget to close sessions when you're done with them
session.close();

// now we request a read-only session, so all servers are eligible for conenctions
// the first server in the list is chosen
session = driver.session(false);
session.close();

// requesting another read-only session will choose the second server
// because of the Round Robin
session = driver.session();
session.close();
}

// when you are done with the driver, just close it
driver.close();
`

___

Enums

#### HAStrategies
- random: It will pick a random server from the pool
- roundRobin: It will round robin through the server pool
- nearest: It will pick the server with the lowest latency

#### HAReadWrite
- masterOnly: Master will be the only queried server
- masterWriteOnlySlaveReadOnly: Master is write-only and slaves are read-only
- masterReadWriteSlaveRead: Master is read-write and slaves are read-only
- all: All servers are read-write
- Custom HAReadWrite Structure
`javascript
{
master: { read: Boolean, write: Boolean },
slave: { read: Boolean, write: Boolean }
}
`

#### Status
- error (-2): Server is returning an error in the HA check
- unknown (-1): Server is in an unknown state
- down ( 0): Server is unreachable
- up ( 1): Server is in the cluster

#### ServerType
- unknown ( 0): Server is in an unknown state
- slave ( 1): Server is a slave
- master ( 2): server is master

___

Instantiating a driver


const driver = new Neo4jHA(serverList, options, readyCallback);

Where:
- serverList: is an array of
- [HTTP URL, BOLT URL]
- {bolt: Bolt URL, url: HTTP URL, auth: {user, pass}}
- options:
- auth: {user, pass} - for all the connections
- strategy: HAStrategies
- rwConfig: HAReadWriteConfig
- neo4jDriverOptions: options passed on the the raw neo4j bolt driver
- checkInterval: interval to check servers availability
- retryOnError: number of times to retry the query until the error is surfaced in callback
- badConnectionsCountAsErrors: true if a server connection error is counted as an error
- readyCallback: callback when all servers status is known

Usage


const session = driver.session(writeLock[, rwConfig, strategy]);

Where:
- writeLock: Boolean - Tell the driver ifif there will ve any writes in the session
- rwConfig: custom HAReadWriteConfig for that session
- strategy`: custom HAStrategies for that session

___

License

License can be found here