doc: Add warning for rest interface limitation #19050

1. 
   fjahr commented at 2:19 pm on May 22, 2020: member

   libevent, which is used for our rest interface, can use up all of the available file descriptors in a system if too many connections are opened at once. If a new block is connected at the same time and can not be written to disk because there are no file descriptors available, the node crashes. Based on my investigation so far the issue is best solved upstream which means we have to wait for the next release (2.2). In the meantime it would be good if we would warn users of this limitation.

   See #11368 for more background.

2. fanquake added the label Docs on May 22, 2020
3. 
   MarcoFalke commented at 2:22 pm on May 22, 2020: member

   Concept ACK
4. 
   laanwj commented at 11:34 am on May 26, 2020: member

   Concept ACK.

   As long as libevent lacks a way to set an upper bound to the number of concurrent incoming connections to a port (it accept()s always), there’s no way we can handle this at our side. It’s always possible to overwhelm the number of file descriptors (especially when connecting through the loopback interface).

5. 
   laanwj commented at 10:47 am on May 28, 2020: member

   Is this specific to the REST interface, though? I think any HTTP-related functionality in bitcoin core is affected by this, including RPC requests (when submitted through HTTP)?
6. doc: Add warnings for http interfaces limitations 5c3eaf9983
7. fjahr force-pushed on May 31, 2020
8. 
   fjahr commented at 10:58 pm on May 31, 2020: member

   Is this specific to the REST interface, though? I think any HTTP-related functionality in bitcoin core is affected by this, including RPC requests (when submitted through HTTP)?

   That is correct (confirmed with another small test). But it seems like we only got reports from people running into the issue via the REST interface. But maybe they just found the issue with the search and did not bother with the distinction. I added the same comment block at the bottom of the JSON-RPC interface doc. Do any other or better places come to mind where I should put it?

9. 
   glozow commented at 9:14 pm on June 16, 2020: member

   Concept ACK. I’m pretty sure there isn’t a good reason to send several hundred requests at once except for not knowing about a more efficient way to get the same information.
10. 
    adamjonas commented at 10:41 pm on December 16, 2020: member

    Pinging the thread. For those that approved of the idea (@MarcoFalke, @glozow, @laanwj), are there any concerns with ACKing this?
11. 
    fjahr commented at 11:55 pm on December 16, 2020: member

    FWIW I am watching libevent 2.2 release effort but it still seems pretty far away: https://github.com/libevent/libevent/issues/1094
12. 
    MarcoFalke commented at 7:55 am on December 17, 2020: member

    Could mention that this is fixed in libevent 2.2 (and later)?
13. 
    fjahr commented at 8:49 am on December 17, 2020: member

    Could mention that this is fixed in libevent 2.2 (and later)?

    It isn’t fixed by libevent 2.2 automatically. It only adds functionality that allows me then to open a PR that fixes it :)

14. 
    MarcoFalke commented at 9:00 am on December 17, 2020: member

    ACK 5c3eaf9983043db1b61a98c95d692a6958670b86
15. MarcoFalke merged this on Dec 17, 2020
16. MarcoFalke closed this on Dec 17, 2020

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fjahr MarcoFalke laanwj glozow adamjonas

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