I included now: SSLProxyEngine on SSLProxyMachineCertificateChainFile /etc/ssl/certs/dfnca.pem (same as SSLCertificateChainFile, I hope that's correct) SSLProxyMachineCertificateFile /etc/ssl/certs/lists.domain.de.cert_key.pem (basically just copied SSLCertificateFile and SSLCertificateKeyFile into one file; and since the keyfile starts with "BEGIN RSA PRIVATE KEY" it seems to fulfill the criteria). SSLProxyProtocol all -SSLv3 -TLSv1 -TLSv1.1
but no change. From apache error log:
[Sun Aug 15 09:19:52.318582 2021] [core:notice] [pid 19706:tid 140315143705728] AH00094: Command line: '/usr/sbin/apache2'
[Sun Aug 15 09:19:52.732381 2021] [proxy_http:error] [pid 19707:tid 140314912167680] (20014)Internal error (specific information not available): [client 37.201.214.82:9292] AH01102: error reading status line
from remote server 127.0.0.1:8000
[Sun Aug 15 09:19:53.929213 2021] [proxy_http:error] [pid 19707:tid 140314912167680] (20014)Internal error (specific information not available): [client 37.201.214.82:9292] AH01102: error reading status line
from remote server 127.0.0.1:8000
[Sun Aug 15 09:19:59.463974 2021] [proxy_http:error] [pid 19708:tid 140314828240640] (20014)Internal error (specific information not available): [client 37.201.214.82:9311] AH01102: error reading status line
from remote server 127.0.0.1:8000
[Sun Aug 15 09:20:03.328416 2021] [proxy_http:error] [pid 19708:tid 140314828240640] (20014)Internal error (specific information not available): [client 37.201.214.82:9311] AH01102: error reading status line
from remote server 127.0.0.1:8000
[Sun Aug 15 09:20:04.605617 2021] [proxy_http:error] [pid 19708:tid 140314828240640] (20014)Internal error (specific information not available): [client 37.201.214.82:9311] AH01102: error reading status line
from remote server 127.0.0.1:8000
[Sun Aug 15 09:20:10.178979 2021] [proxy_http:error] [pid 19708:tid 140314828240640] (20014)Internal error (specific information not available): [client 37.201.214.82:9305] AH01102: error reading status line
from remote server 127.0.0.1:8000