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Charlie is a node module keeps of success and failures of network requests and adises on a delay between attempts using the backoff algorithm described in Exponential Backoff in Distributed Systems.

This module skips upto three failures before starting the backoff.

npm install charlie

Before making a request to an origin, let charlie know. This functiont akes three arguments:

• keys: An array of keys used to identify the network resource. For HTTP requests, the keys could be the URI of the resource, or the IP address, or the host name etc.
• minDelay: Minimum backoff delay. As suggested in the blog post above, choose a value under which 99% of requests complete.
• maxDelay: Maximum backoff delay. Choose an acceptable value based on availability requirements.

This function returns a decision with three fields:

• state: values are go or nogo
• count: number of failures so far. The count is reset after a success.
• delay: currently applied backoff delay

Here is an example.

// Arr is an array of keys used to identify the network resource.
var decision = charlie.ask(arr, minDelay, maxDelay);
if(decision.state === 'go') {
    // make the request
}
else {
    // don't make the request
    console.log('Waiting until ' + decision.delay);
}

When a request succeeds, tell charlie.

charlie.ok(arr);

When the request fails, tell charlie any way.

charlie.notok(arr);

Forget everything about the resource.

charlie.clear(arr);