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.

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

HTTPS:

`js
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.

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`bash
npm install electrode-keepalive --save
`

APIs

Properties

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

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

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ElectrodeKeepAlive.DNS_CACHE - Internal DNS cache mapping object.

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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

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

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

Methods

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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.

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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.

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instance.getName(options)

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

[settings]: https://nodejs.org/api/http.html#http_new_agent_options
[agentkeepalive]: https://github.com/node-modules/agentkeepalive

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instance.getNameAsync(options, callback)`

Async version of getName.