JSPM

title: Retry Link

Purpose

An Apollo Link to allow multiple attempts when an operation has failed, due to network or server errors. RetryLink provides exponential backoff, and jitters delays between attempts by default. It does not (currently) support retries for GraphQL errors.

One such use case is to try a request while a network connection is offline and retry until it comes back online.

Installation

npm install apollo-link-retry --save

Usage

import { RetryLink } from "apollo-link-retry";

const link = new RetryLink();

Options

The standard retry strategy provides exponential backoff with jittering, and takes the following options, grouped into delay and attempt strategies:

• delay.initial: The number of milliseconds to wait before attempting the first retry.

• delay.max: The maximum number of milliseconds that the link should wait for any retry.

• delay.jitter: Whether delays between attempts should be randomized.

• attempts.max: The max number of times to try a single operation before giving up.

• attempts.retryIf: A predicate function that can determine whether a particular response should be retried.

The default configuration is equivalent to:

new RetryLink({
  delay: {
    initial: 300,
    max: Infinity,
    jitter: true,
  },
  attempts: {
    max: 5,
    retryIf: (error, _operation) => !!error,
  },
});

On Exponential Backoff & Jitter

Starting with initialDelay, the delay of each subsequent retry is increased exponentially (by a power of 2). For example, if initialDelay is 100, additional retries will occur after delays of 200, 400, 800, etc.

Additionally, with jitter enabled, delays are randomized anywhere between 0ms (instant), and 2x the configured delay so that, on average, they should occur at the same intervals.

These two features combined help alleviate the thundering herd problem, by distributing load during major outages.

Custom Strategies

Instead of the options object, you may pass a function for delay and/or attempts, which implement custom strategies for each. In both cases the function is given the same arguments (count, operation, error).

The attempts function should return a boolean indicating whether the response should be retried. If yes, the delay function is then called, and should return the number of milliseconds to delay by.

import { RetryLink } from "apollo-link-retry";

const link = new RetryLink(
  attempts: (count, operation, error) => {
    return !!error && operation.operationName != 'specialCase';
  },
  delay: (count, operation, error) => {
    return count * 1000 * Math.random();
  },
});

Context

The Retry Link does not use the context for anything.