budgeteer

Cost-based event rate limiter, scheduler, and deduplicator. Uses a Redis
backend. Provides the "brain" of a simple job scheduling system.

Features:

- Event deduplication: Events that have already been processed, or are
scheduled for delayed processing, are dropped.
- Cost based accounting, giving each key a token budget per day. Clients
are free to model costs any way they like. Typically, execution time (in
seconds) is a major input into the cost function.
- Delay and retry scheduling: An execution delay is calculated once an event's
budget turns negative. The delay is proportional to the time it takes to
even out the budget, based on the token_budget_per_day configuration
option.

Usage example

``javascript
const budgeteer = new Budgeteer({
store: {
type: 'redis', // Default & only supported storage type so far.
host: 'redishost',
port: 12345,
ttl: 86400 * 7 // Store rate limiting / dedup information for 7 days
}
});
const key = 'someName';

// Token budget configuration, typically differs per event type.
const token_budget = {
tokens_per_day: 24, // Steady state token rate.
max_balance: 36 // Maximum balance available for bursts, when a job is
// new or has not been executed in a long time.
};

return budgeteer.check(key, token_budget, req.startTime)
.then(res => {
if (res.isDuplicate) {
// Duplicate. Drop the event.
return;
}
if (res.delay) {
// add event to a (Kafka) delay queue, based on the suggested delay.
return enqueueToDelayQueue(event, delay)
// Redis read / write.
.then(() => budgeteer.reportScheduled(key, token_budget, 0);
} else {
const startTime = Date.now();
// execute event
return process_event(event)
// Redis read / write.
.then(() => budgeteer.reportSuccess(key, token_budget, startTime, (Date.now() - startTime) / 1000))
.catch(e => {
// Time plus some failure penalty
const cost = (Date.now() - startTime) / 1000 + 1;
return budgeteer.check(key, token_budget, req.startTime, cost)
.then(res => {
if (!res.isDuplicate) {
// We choose to enforce a minimum retry delay of 200 seconds.
delay = Math.max(delay, 200);
return enqueueToDelayQueue(event, delay)
// Redis read / write.
.then(() => budgeteer.reportScheduled(key, token_budget, cost));
}
});
})
}
})
``