How Uber Protects Against Retry Storms

(uber.com)

15 points | by iscmt 2 hours ago

2 comments

  • maxchisto 18 minutes ago
    I'm suspicious of load shedding not mentioned in the article. Combine that with exp backoff in the caller and you got yourself a pretty robust starting point
  • aftbit 45 minutes ago
    I'd be interested to hear other strategies in this space. I've done the naive thing of allowing retries everywhere, and gotten into retry storms. When I was next presented with the problem, I tried the other naive thing of only allowing retries from the very top level service, which led me to redoing absolutely tons of work for each failure. What's a nice middle path that doesn't add too much complexity?
    • CBLT 7 minutes ago
      There's a good amount of literature about this (check the other comments), but you can vastly simplify this into two things you need to do:

      1. Your service that retries should have some retry budget. This is a good place to be "smart", because you can reason entirely locally instead of turning it into a distributed systems problem. The best library I've seen for this was doing Exponential Moving Average of requests per second sent down that pipe (not counting retries) and only allowing 20% more requests per second as retries, total. Each individual request could be retried 3 times. This was critical as it bounds the additional load from retries.

      2. Whenever a service retries but has to give up, the error it sends to its callers should never be retried. There has to be some agreement that that HTTP code will never be retried. This prevents the multiplicative factor of retry on top of retry, which is why those storms can generate so much load.

      Everything else is nice-to-have, but those two alone should bound the total requests you get in a retry storm.

    • otterley 27 minutes ago
    • sroussey 32 minutes ago
      So many variables, but the simple thing is to set things up like normal rate limiting (which you would want to do anyways). The one generating the errors passes back a retry time. You can add jitter here, tell low priority requests to wait longer, etc.

      BTW: do keep track of priority. It’s like having a database that gets flooded with connections and won’t allow new ones in—but will for admin users (btw, it did not used to be that way in the early days of MySQL).

    • tregoning 32 minutes ago
      • sroussey 26 minutes ago
        Yes, exponential back off and jitter are the first things to work on, and good if you don’t have a better signal (like loss of network).

        Also, a simple signal status server or queue system helps to keep global state such that everyone doesn’t retry all at once.

        If you have a central error rate server you can skip your retry based on the error rate (100% error rate, don’t retry, etc).

      • anonymars 29 minutes ago
        • applfanboysbgon 26 minutes ago
          This is trading a good developer experience for a bad user experience. There are situations where it makes sense to force manual retry, but there's no reason to apply one universal rule to all possible situations. Lack of considering nuance for your situation is just intellectual laziness.
    • sfraxo 19 minutes ago
      [flagged]