Azure功能需要冷却多久才能扩展?

我们可以查看源代码并尝试至少理解部分功能。实际上,它基于计时器和worker的概念,worker更新它们的状态,并让运行时决定是否需要放大或缩小。

整体算法描述如下:

protected virtual async Task MakeScaleDecision(string activityId, IWorkerInfo manager)
{
    if (DateTime.UtcNow < _scaleCheckUtc)
    {
        return;
    }

    try
    {
        var workers = await _table.ListNonStale();
        _tracer.TraceInformation(activityId, manager, workers.GetSummary("NonStale"));

        if (await TryRemoveIfMaxWorkers(activityId, workers, manager))
        {
            return;
        }

        if (await TryAddIfLoadFactorMaxWorker(activityId, workers, manager))
        {
            return;
        }

        if (await TrySwapIfLoadFactorMinWorker(activityId, workers, manager))
        {
            return;
        }

        if (await TryAddIfMaxBusyWorkerRatio(activityId, workers, manager))
        {
            return;
        }

        if (await TryRemoveIfMaxFreeWorkerRatio(activityId, workers, manager))
        {
            return;
        }

        if (await TryRemoveSlaveWorker(activityId, workers, manager))
        {
            return;
        }
    }
    catch (Exception ex)
    {
        _tracer.TraceError(activityId, manager, string.Format("MakeScaleDecision failed with {0}", ex));
    }
    finally
    {
        _scaleCheckUtc = DateTime.UtcNow.Add(_settings.ScaleCheckInterval);
    }
}

更重要的是,在源代码中还可以找到为什么会看到活着的工人的答案:

protected virtual async Task PingWorker(string activityId, IWorkerInfo worker)
{
    // if ping was unsuccessful, keep pinging.  this is to address
    // the issue where site continue to run on an unassigned worker.
    if (!_pingResult || _pingWorkerUtc < DateTime.UtcNow)
    {
        // if PingWorker throws, we will not update the worker status
        // this worker will be stale and eventually removed.
        _pingResult = await _eventHandler.PingWorker(activityId, worker);

        _pingWorkerUtc = DateTime.UtcNow.Add(_settings.WorkerPingInterval);
    }

    // check if worker is valid for the site
    if (_pingResult)
    {
        await _table.AddOrUpdate(worker);

        _tracer.TraceUpdateWorker(activityId, worker, string.Format("Worker loadfactor {0} updated", worker.LoadFactor));
    }
    else
    {
        _tracer.TraceWarning(activityId, worker, string.Format("Worker does not belong to the site."));

        await _table.Delete(worker);

        _tracer.TraceRemoveWorker(activityId, worker, "Worker removed");

        throw new InvalidOperationException("The worker does not belong to the site.");
    }
}

不幸的是,实现的某些部分是密封的(例如 IWorkerInfo ),所以你无法了解全貌,我们只能猜测(或询问;)

函数确实有一些启发式方法,可以根据均衡量和资源利用率来确定何时扩展和何时扩展。在过去,他们相当节俭,但这并没有提供足够好的扩张步伐。现在,他们倾向于在资源调配过多而不是过少方面犯错误。

好消息是,除了出于好奇之外,你不应该真的关心扩展。你不用为闲置的服务器付费。