charlie

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 applies skips upto three failures before starting the backoff.

Getting Charlie

npm install charlie

Usage

charlie.ask

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);
}

charlie.ok

When a request succeeds, tell charlie.

charlie.ok(arr);

charlie.notok

When the request fails, tell charlie any way.

charlie.notok(arr);

charlie.clear

Forget everything about the resource.

charlie.clear(arr);