flood detected with file uploads over http2

[Jasper Wallace]

We are having intermittent problems uploading files via nginx to a
flask backend over http2:

2019/12/16 16:07:08 [debug] 27658#27658: *1 event timer: 3, old:
1576512608187, new: 1576512608301
2019/12/16 16:07:08 [debug] 27658#27658: *1 http2 idle handler
2019/12/16 16:07:08 [info] 27658#27658: *1 http2 flood detected while
processing HTTP/2 connection, client: x.x.x.x, server: 0.0.0.0:443
2019/12/16 16:07:08 [debug] 27658#27658: *1 http2 send GOAWAY frame, status:0
2019/12/16 16:07:08 [debug] 27658#27658: *1 posix_memalign:
0000563642B8EE20:512 @16
2019/12/16 16:07:08 [debug] 27658#27658: *1 http2 frame out:
0000563642B8EE40 sid:0 bl:0 len:8
2019/12/16 16:07:08 [debug] 27658#27658: *1 malloc: 0000563642D0A870:16384
2019/12/16 16:07:08 [debug] 27658#27658: *1 SSL buf copy: 17
2019/12/16 16:07:08 [debug] 27658#27658: *1 SSL to write: 17

Is there anyway of getting information on what might be triggering this?

We've changed some defaults:

client_max_body_size 10m;
http2_body_preread_size 256k;
http2_recv_buffer_size 1m;
proxy_headers_hash_max_size 512;
proxy_headers_hash_bucket_size 128;

Client is Chrome:

Version 78.0.3904.97 (Developer Build) built on Debian 10.1, running
on Debian 10.2 (64-bit)

openssl:

OpenSSL 1.1.0l  10 Sep 2019

nginx:

nginx version: nginx/1.10.3
built with OpenSSL 1.1.0k  28 May 2019 (running with OpenSSL 1.1.0l
10 Sep 2019)
TLS SNI support enabled
configure arguments: --with-cc-opt='-g -O2
-fdebug-prefix-map=/build/nginx-DhOtPd/nginx-1.10.3=.
-fstack-protector-strong -Wformat -Werror=format-security -Wdate-time
-D_FORTIFY_SOURCE=2' --with-ld-opt='-Wl,-z,relro -Wl,-z,now'
--prefix=/usr/share/nginx --conf-path=/etc/nginx/nginx.conf
--http-log-path=/var/log/nginx/access.log
--error-log-path=/var/log/nginx/error.log
--lock-path=/var/lock/nginx.lock --pid-path=/run/nginx.pid
--modules-path=/usr/lib/nginx/modules
--http-client-body-temp-path=/var/lib/nginx/body
--http-fastcgi-temp-path=/var/lib/nginx/fastcgi
--http-proxy-temp-path=/var/lib/nginx/proxy
--http-scgi-temp-path=/var/lib/nginx/scgi
--http-uwsgi-temp-path=/var/lib/nginx/uwsgi --with-debug
--with-pcre-jit --with-ipv6 --with-http_ssl_module
--with-http_stub_status_module --with-http_realip_module
--with-http_auth_request_module --with-http_v2_module
--with-http_dav_module --with-http_slice_module --with-threads
--with-http_addition_module --with-http_flv_module
--with-http_geoip_module=dynamic --with-http_gunzip_module
--with-http_gzip_static_module --with-http_image_filter_module=dynamic
--with-http_mp4_module --with-http_perl_module=dynamic
--with-http_random_index_module --with-http_secure_link_module
--with-http_sub_module --with-http_xslt_module=dynamic
--with-mail=dynamic --with-mail_ssl_module --with-stream=dynamic
--with-stream_ssl_module
--add-dynamic-module=/build/nginx-DhOtPd/nginx-1.10.3/debian/modules/headers-more-nginx-module
--add-dynamic-module=/build/nginx-DhOtPd/nginx-1.10.3/debian/modules/nginx-auth-pam
--add-dynamic-module=/build/nginx-DhOtPd/nginx-1.10.3/debian/modules/nginx-cache-purge
--add-dynamic-module=/build/nginx-DhOtPd/nginx-1.10.3/debian/modules/nginx-dav-ext-module
--add-dynamic-module=/build/nginx-DhOtPd/nginx-1.10.3/debian/modules/nginx-development-kit
--add-dynamic-module=/build/nginx-DhOtPd/nginx-1.10.3/debian/modules/nginx-echo
--add-dynamic-module=/build/nginx-DhOtPd/nginx-1.10.3/debian/modules/ngx-fancyindex
--add-dynamic-module=/build/nginx-DhOtPd/nginx-1.10.3/debian/modules/nchan
--add-dynamic-module=/build/nginx-DhOtPd/nginx-1.10.3/debian/modules/nginx-lua
--add-dynamic-module=/build/nginx-DhOtPd/nginx-1.10.3/debian/modules/nginx-upload-progress
--add-dynamic-module=/build/nginx-DhOtPd/nginx-1.10.3/debian/modules/nginx-upstream-fair
--add-dynamic-module=/build/nginx-DhOtPd/nginx-1.10.3/debian/modules/ngx_http_substitutions_filter_module

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