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  1. JDK
  2. JDK-8304885

Reuse stale data to improve DNS resolver resiliency

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        Discussion on net-dev@ https://mail.openjdk.org/pipermail/net-dev/2023-March/020682.html

        One of the main issue I try to solve is how the cache handle the intermittent DNS server outages due to overloading or network connection.

        At the moment this cache can be configured by the application using the following two properties:
           (1) "networkaddress.cache.ttl"(30 sec) - cache policy for successful lookups
           (2) "networkaddress.cache.negative.ttl"(10 sec) - cache policy for negative lookups

        Default timeout for positive responses is good enough to "have recent dns-records" and to "minimize the amount of requests to the DNS server".

        But the cache for the negative responses is problematic. This is a problem I would like to solve. Caching the negative response means that for **10** seconds the application will not be able to connect to the server.

        Possible solutions:
          1. Decreasing timeout "for the negative responses": unfortunately more requests to the server at the moment of "DNS-outage" cause even more issues, since this is not the right moment to load network/server more.
          2. Increasing timeout "for the positive responses": this will decrease the chance to get an error, but the cache will start to use stale data longer.
          3. This proposal: it would be good to ignore the negative response and continue to use result of the last "successful lookup" until some additional timeout.

        The idea is to split the notion of the TTL and the timeout used for the cache. When TTL for the record will expire we should request the new data from the server. If this request goes fine we will update the record, if it fails we will continue to use the cached date until next sync.

        For example if the new property "networkaddress.extended.cache.ttl" is set to 10 minutes, then we will cache positive response for 10 minutes but will try to sync it every 30 seconds. If the new property is not set then as before we will cache positive for 30 seconds and then cache negative response for 10 seconds.


        RFC 8767 Serving Stale Data to Improve DNS Resiliency:
        https://www.rfc-editor.org/rfc/rfc8767

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                serb Sergey Bylokhov
                serb Sergey Bylokhov
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