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  1. Couchbase Server
  2. MB-44182

[BP 6.6.2] - XDCR TCP connection leak when host does not respond and XDCR retries



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      Based on a customer set up, it is possible in a very rare case for goxdcr to leak connections and end up taking up all the file descriptors of a system. 

      (Below is finding from the customer's case without the customer reference)
      This is the code to clean up any failed REST calls, such as to ns_server:

      2167 			transport, ok := client.Transport.(*http.Transport)
      2168 			if ok {
      2169 				if u.IsSeriousNetError(err) {
      2170 					logger.Debugf("Encountered %v, close all idle connections for this http client.\n", err)
      2171 				}
      2172 				transport.CloseIdleConnections()
      2173 			}

      The suspect thing is that it is possible for transport not to be set. As is the case, for http calls (to local ns_server, we don’t encrypt), goxdcr doesn’t set the transport:


       		client = &http.Client{Timeout: base.DefaultHttpTimeout}

      If transport is not set, then we’re not closing idle connection, and depending on golang to close it for us.

      It just so happens that golang has had an issue https://github.com/golang/go/issues/28012 that showcases how TCP connection is not closed if the server doesn’t respond.
      In particular, the user posted a code snip that is exactly how XDCR creates the http client. See https://github.com/golang/go/issues/28012#issuecomment-562290662 and he claims that the TCP connection isn’t closed.

      This issue was fixed Dec 11, 2019 in golang 1.14, with the tile: “net/http: don't wait indefinitely in Transport for proxy CONNECT response”.

      XDCR for 6.5.1 is shipped with golang 1.11 according to CMakefile. The golang issue I mentioned was filed with the OP using 1.11 as well.


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              pavithra.mahamani Pavithra Mahamani (Inactive)
              neil.huang Neil Huang
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