Hello.
We have an existing Apache server (version 2.4.25 on Debian stretch) hosting a
web application on which we want to activate mod_http2. The Apache server is
only a reverse HTTP proxy (using mpm_event) on our application . We followed
the instructions (http://httpd.apache.org/docs/2.4/en/howto/http2.html) to do
the setup and it seemed to work at first.
Our application uses a persistent Server Side Event request per browser tab
(which is the main reason we want to switch to http/2). This persistent
request is managed by pushpin (https://pushpin.org).
When several users play with the application for a while and open several
browser tabs, some requests get stuck and stay in "pending" state forever.
When a browser tab gets stuck, all further requests are stuck in other tabs
too.
What we've tried:
- increasing H2MaxWorkers to 120 (more than the number of users*number of
browser tabs) improves the behavior but we still get some stuck requests
- with H2MaxWorkers = 3 we get stuck requests with only a small number of
opened browser tabs
- updating Apache to 2.4.43 still get stuck requests
- when mod_http2 is disabled we do not get stuck requests
- if we do not keep persistent SSE requests we do not get stuck requests
- changing the mpm to mpm_worker also seems to improve the situation: we get
stuck requests but the response comes back with a delay (some seconds).
The Apache error log (LogLevel warn) does not print anything when stuck
requests occur.
We understand that each persistent request occupies a mod_http2 worker, but
not why this has an effect on other requests.
Would somebody have an idea to explain this behavior? I can provide detailed
logs and other information on our setup if needed.
S?bastien Grignard.
Algoo SAS
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We have an existing Apache server (version 2.4.25 on Debian stretch) hosting a
web application on which we want to activate mod_http2. The Apache server is
only a reverse HTTP proxy (using mpm_event) on our application . We followed
the instructions (http://httpd.apache.org/docs/2.4/en/howto/http2.html) to do
the setup and it seemed to work at first.
Our application uses a persistent Server Side Event request per browser tab
(which is the main reason we want to switch to http/2). This persistent
request is managed by pushpin (https://pushpin.org).
When several users play with the application for a while and open several
browser tabs, some requests get stuck and stay in "pending" state forever.
When a browser tab gets stuck, all further requests are stuck in other tabs
too.
What we've tried:
- increasing H2MaxWorkers to 120 (more than the number of users*number of
browser tabs) improves the behavior but we still get some stuck requests
- with H2MaxWorkers = 3 we get stuck requests with only a small number of
opened browser tabs
- updating Apache to 2.4.43 still get stuck requests
- when mod_http2 is disabled we do not get stuck requests
- if we do not keep persistent SSE requests we do not get stuck requests
- changing the mpm to mpm_worker also seems to improve the situation: we get
stuck requests but the response comes back with a delay (some seconds).
The Apache error log (LogLevel warn) does not print anything when stuck
requests occur.
We understand that each persistent request occupies a mod_http2 worker, but
not why this has an effect on other requests.
Would somebody have an idea to explain this behavior? I can provide detailed
logs and other information on our setup if needed.
S?bastien Grignard.
Algoo SAS
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