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From Eric Covener <cove...@gmail.com>
Subject Re: backend connections life times
Date Wed, 30 Jun 2021 16:01:52 GMT
On Wed, Jun 30, 2021 at 11:46 AM Stefan Eissing
<stefan.eissing@greenbytes.de> wrote:
>
> It looks like we stumbled upon an issue in https://bz.apache.org/bugzilla/show_bug.cgi?id=65402
which concerns the life times of our backend connections.
>
> When a frontend connection causes a backend request and drops, our backend connection
only notifies the loss when it attempts to pass some data. In normal http response processing,
this is not an issue since response chunks are usually coming in quite frequently. Then the
proxied connection will fail to pass it to an aborted frontend connection and cleanup will
occur.
>
> However, with such modern shenanigans such as Server Side Events (SSE), the request is
supposed to be long running and will produce body chunks quite infrequently, like every 30
seconds or so. This leaves our proxy workers hanging in recv for quite a while and may lead
to worker exhaustion.
>
> We can say SSE is a bad idea anyway, but that will probably not stop people from doing
such crazy things.
>
> What other mitigations do we have?
> - pthread_kill() will interrupt the recv and probably make it fail
> - we can use shorter socket timeouts on backend and check r->connection status in
between
> - ???


In trunk the tunnelling side of mod_proxy_http can go async and get
called back for activity on either side by asking Event to watch both
sockets.

I'm not sure how browsers treat the SSE connection, can it ever have a
subsequent request?  If not, maybe we could see the SSE Content-Type
and shoehorn it into the tunneling (figuring out what to do with
writes from the client, backport the event and async tunnel stuff?)

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