electrode-keepalive

electrode-keepalive provides an keep-alive HttpAgent capable of maintaining and tracking available sockets using IP address and hostname as key. This allows for graceful handling of DNS changes or failover when routing configuration is updated. It resolves part of the problems in this issue

It also uses the patched agentkeepalive to support destroying kept alive sockets within a timeout.

The big changes from agentkeepalive are:

1. Do DNS lookup and use host and IP address as key to track sockets.
2. Use LIFO instead of FIFO when reusing free sockets. This solves issue of free sockets stay around too long, because after a burst of traffic, node creates a long list of free sockets, and continuous traffic would cycle through and prevent them from expiring.

Usage

const ElectrodeKeepAlive = require("electrode-keepalive");
const keepAlive = new ElectrodeKeepAlive();
request({ url: "http://www.google.com", agent: keepAlive.agent });

HTTPS:

const ElectrodeKeepAlive = require("electrode-keepalive");
const keepAlive = new ElectrodeKeepAlive({ https: true });
request({ url: "https://www.google.com", agent: keepAlive.agent });

See contructor for details on options you can passed.

Install

npm install electrode-keepalive --save

APIs

Properties

agent

instance.agent - Returns the http/https agent. (readonly)

https

instance.https - If true, then the agent is an https agent. (readonly)

static DNS_CACHE

ElectrodeKeepAlive.DNS_CACHE - Internal DNS cache mapping object.

static checkExpiredDnsInterval

ElectrodeKeepAlive.checkExpiredDnsInterval - Interval in milliseconds to check and delete expired DNS cache entries. Default: 5000ms

This is not a regular timer interval. The check only occurs when preLookup is called.

Static Methods

static clearDnsCache

ElectrodeKeepAlive.clearDnsCache() - Wipes out current DNS mapping.

static deleteExpiredDnsCache

ElectrodeKeepAlive.deleteExpiredDnsCache() - delete any DNS cache entry that's expired.

Methods

constructor

constructor(options)

Creates an instance of ElectrodeKeepAlive.

• options should be the default http agent settings that are passed through to the underlying implementation. Additionally the following options are supported:

  • https - If true, then creates an https Agent.
  • expiry - The duration (in milliseconds) that ip entries in the DNS mapping will be refreshed. Default: 5000ms

• Since this uses agentkeepalive, you can also pass in any options it supports.

  • The defaults for the following two options are set if you didn't specify them:
    • freeSocketKeepAliveTimeout - 30000ms
    • timeout - 60000ms

• keepAlive - This is always default to true by ElectrodeKeepAlive.

preLookup

instance.preLookup(host, options, callback)

This method is used to do DNS lookup to translate host name into IP for tracking free sockets. It will also populate ElectrodeKeepAlive DNS cache.

The arguments matches Node dns module lookup.

getName

instance.getName(options)

The internal method to override http agent's default getName. Not intended for public use.

getNameAsync

instance.getNameAsync(options, callback)

Async version of getName.