TanTan
2a69b23b47
Dev Build / cleanup (push) Canceled after 0s
Dev Build / typecheck (push) Canceled after 0s
Dev Build / build (linux-arm64, ubuntu-24.04-arm, linux-arm64) (push) Canceled after 0s
Dev Build / build (linux-x64, ubuntu-latest, linux-x64) (push) Canceled after 0s
Dev Build / build (win-x64, windows-latest, win32-x64) (push) Canceled after 0s
Dev Build / dispatch-dev-docker (push) Skipped
240 lines
6.8 KiB
Plaintext
240 lines
6.8 KiB
Plaintext
# RoundRobinPool
|
|
|
|
<!--introduced_in=v7.17.0-->
|
|
<!--type=module-->
|
|
<!-- source_link=lib/dispatcher/round-robin-pool.js -->
|
|
|
|
> Stability: 2 - Stable
|
|
|
|
A pool of [`Client`][] instances connected to the same upstream target that
|
|
selects clients in a round-robin fashion.
|
|
|
|
Unlike [`Pool`][], which always reuses the first available client,
|
|
`RoundRobinPool` cycles through its clients so that requests are distributed
|
|
evenly across every open connection. This is useful when the upstream target is
|
|
fronted by a load balancer that distributes TCP connections across multiple
|
|
backend servers (for example, a Kubernetes Service): each connection is pinned
|
|
to a backend by the load balancer, and `RoundRobinPool` spreads requests across
|
|
those connections so every backend receives a comparable share of traffic.
|
|
|
|
Requests are not guaranteed to be dispatched in the order they were invoked.
|
|
|
|
```mjs
|
|
import { RoundRobinPool } from 'undici'
|
|
|
|
const pool = new RoundRobinPool('http://localhost:3000', { connections: 10 })
|
|
```
|
|
|
|
`RoundRobinPool` distributes HTTP requests evenly across TCP connections, not
|
|
across backend servers directly. Even backend distribution therefore depends on
|
|
the load balancer assigning different connections to different backends (for
|
|
example, round-robin, random, or least-connections without client affinity). If
|
|
the load balancer pins all connections from one source to the same backend (for
|
|
example, source-IP affinity or sticky sessions), consider [`BalancedPool`][]
|
|
with the individual backend addresses instead.
|
|
|
|
## Class: `RoundRobinPool`
|
|
|
|
<!-- YAML
|
|
added: v7.17.0
|
|
-->
|
|
|
|
* Extends: {Dispatcher}
|
|
|
|
### `new RoundRobinPool(url[, options])`
|
|
|
|
<!-- YAML
|
|
added: v7.17.0
|
|
-->
|
|
|
|
* `url` {URL|string} The upstream target. It should only include the
|
|
**protocol, hostname, and port**.
|
|
* `options` {RoundRobinPoolOptions} (optional)
|
|
|
|
#### Parameter: `RoundRobinPoolOptions`
|
|
|
|
Extends: {ClientOptions}
|
|
|
|
* `factory` {Function} A function used to create the underlying {Client}
|
|
instances. **Default:** `(origin, opts) => new Client(origin, opts)`.
|
|
* `origin` {URL}
|
|
* `opts` {Object}
|
|
* Returns: {Dispatcher}
|
|
* `connections` {number|null} (optional) The maximum number of {Client}
|
|
instances to create. When set to `null`, the `RoundRobinPool` instance creates
|
|
an unlimited number of {Client} instances. **Default:** `null`.
|
|
* `clientTtl` {number|null} (optional) The amount of time, in milliseconds,
|
|
before a {Client} instance is removed from the `RoundRobinPool` and closed.
|
|
When set to `null`, {Client} instances are not removed or closed based on age.
|
|
**Default:** `null`.
|
|
|
|
`RoundRobinPool` inherits all [`Client`][] options. A [`Client`][] instance is
|
|
created lazily on the first dispatch and additional instances are created on
|
|
demand, up to `connections`, when every existing client is busy.
|
|
|
|
### `roundRobinPool.closed`
|
|
|
|
<!-- YAML
|
|
added: v7.17.0
|
|
-->
|
|
|
|
* Type: {boolean}
|
|
|
|
`true` after `roundRobinPool.close()` has been called.
|
|
|
|
### `roundRobinPool.destroyed`
|
|
|
|
<!-- YAML
|
|
added: v7.17.0
|
|
-->
|
|
|
|
* Type: {boolean}
|
|
|
|
`true` after `roundRobinPool.destroy()` has been called, or after
|
|
`roundRobinPool.close()` has been called and the pool shutdown has completed.
|
|
|
|
### `roundRobinPool.stats`
|
|
|
|
<!-- YAML
|
|
added: v7.17.0
|
|
-->
|
|
|
|
* Type: {PoolStats}
|
|
|
|
Aggregate connection statistics for the pool. See [`PoolStats`][].
|
|
|
|
### `roundRobinPool.close([callback])`
|
|
|
|
<!-- YAML
|
|
added: v7.17.0
|
|
-->
|
|
|
|
Closes the pool and gracefully waits for enqueued requests to complete before
|
|
resolving. Implements [`dispatcher.close([callback])`][].
|
|
|
|
### `roundRobinPool.destroy([error[, callback]])`
|
|
|
|
<!-- YAML
|
|
added: v7.17.0
|
|
-->
|
|
|
|
Destroys the pool abruptly. All pending and running requests are aborted with
|
|
the given `error`. Implements [`dispatcher.destroy([error[, callback]])`][].
|
|
|
|
### `roundRobinPool.connect(options[, callback])`
|
|
|
|
<!-- YAML
|
|
added: v7.17.0
|
|
-->
|
|
|
|
Starts two-way communications with the requested resource using
|
|
[HTTP CONNECT][]. See [`dispatcher.connect(options[, callback])`][].
|
|
|
|
### `roundRobinPool.dispatch(options, handler)`
|
|
|
|
<!-- YAML
|
|
added: v7.17.0
|
|
-->
|
|
|
|
Dispatches a request through the next client selected in round-robin order.
|
|
Implements [`dispatcher.dispatch(options, handler)`][].
|
|
|
|
### `roundRobinPool.pipeline(options, handler)`
|
|
|
|
<!-- YAML
|
|
added: v7.17.0
|
|
-->
|
|
|
|
For easy use with [`stream.pipeline`][]. See
|
|
[`dispatcher.pipeline(options, handler)`][].
|
|
|
|
### `roundRobinPool.request(options[, callback])`
|
|
|
|
<!-- YAML
|
|
added: v7.17.0
|
|
-->
|
|
|
|
Performs an HTTP request. See [`dispatcher.request(options[, callback])`][].
|
|
|
|
### `roundRobinPool.stream(options, factory[, callback])`
|
|
|
|
<!-- YAML
|
|
added: v7.17.0
|
|
-->
|
|
|
|
A faster version of [`roundRobinPool.request()`][]. See
|
|
[`dispatcher.stream(options, factory[, callback])`][].
|
|
|
|
### `roundRobinPool.upgrade(options[, callback])`
|
|
|
|
<!-- YAML
|
|
added: v7.17.0
|
|
-->
|
|
|
|
Upgrades a connection to a different protocol. See
|
|
[`dispatcher.upgrade(options[, callback])`][].
|
|
|
|
### Event: `'connect'`
|
|
|
|
<!-- YAML
|
|
added: v7.17.0
|
|
-->
|
|
|
|
See [Dispatcher Event: `'connect'`][].
|
|
|
|
### Event: `'disconnect'`
|
|
|
|
<!-- YAML
|
|
added: v7.17.0
|
|
-->
|
|
|
|
See [Dispatcher Event: `'disconnect'`][].
|
|
|
|
### Event: `'drain'`
|
|
|
|
<!-- YAML
|
|
added: v7.17.0
|
|
-->
|
|
|
|
See [Dispatcher Event: `'drain'`][].
|
|
|
|
## Example
|
|
|
|
```mjs
|
|
import { RoundRobinPool } from 'undici'
|
|
|
|
const pool = new RoundRobinPool('http://localhost:3000', {
|
|
connections: 10
|
|
})
|
|
|
|
// Requests are distributed evenly across all 10 connections.
|
|
for (let i = 0; i < 100; i++) {
|
|
const { body } = await pool.request({
|
|
path: '/api/data',
|
|
method: 'GET'
|
|
})
|
|
console.log(await body.json())
|
|
}
|
|
|
|
await pool.close()
|
|
```
|
|
|
|
[HTTP CONNECT]: https://developer.mozilla.org/docs/Web/HTTP/Methods/CONNECT
|
|
[`BalancedPool`]: BalancedPool.md#class-balancedpool
|
|
[`Client`]: Client.md#class-client
|
|
[`Pool`]: Pool.md#class-pool
|
|
[`PoolStats`]: PoolStats.md#class-poolstats
|
|
[`dispatcher.close([callback])`]: Dispatcher.md#dispatcherclosecallback-promise
|
|
[`dispatcher.connect(options[, callback])`]: Dispatcher.md#dispatcherconnectoptions-callback
|
|
[`dispatcher.destroy([error[, callback]])`]: Dispatcher.md#dispatcherdestroyerror-callback-promise
|
|
[`dispatcher.dispatch(options, handler)`]: Dispatcher.md#dispatcherdispatchoptions-handler
|
|
[`dispatcher.pipeline(options, handler)`]: Dispatcher.md#dispatcherpipelineoptions-handler
|
|
[`dispatcher.request(options[, callback])`]: Dispatcher.md#dispatcherrequestoptions-callback
|
|
[`dispatcher.stream(options, factory[, callback])`]: Dispatcher.md#dispatcherstreamoptions-factory-callback
|
|
[`dispatcher.upgrade(options[, callback])`]: Dispatcher.md#dispatcherupgradeoptions-callback
|
|
[`roundRobinPool.request()`]: #roundrobinpoolrequestoptions-callback
|
|
[`stream.pipeline`]: https://nodejs.org/api/stream.html#streampipelinesource-transforms-destination-callback
|
|
[Dispatcher Event: `'connect'`]: Dispatcher.md#event-connect
|
|
[Dispatcher Event: `'disconnect'`]: Dispatcher.md#event-disconnect
|
|
[Dispatcher Event: `'drain'`]: Dispatcher.md#event-drain
|