Reverse Proxy Error reading from remote server

[Sverre Moe]

Recently we have been getting an Proxy Error each time we try to change some configuration in Jenkins.

On Save and Apply, Jenkins gives us the following error:

  Proxy Error

  The proxy server received an invalid response from an upstream server.

  The proxy server could not handle the request

  Reason: Error reading from remote server

It happens only on Save/Apply. All other access to Jenkins works fine.

Happens with:

Jenkins LTS 2.277.4 (several plugins not updated)

Jenkins LTS 2.289.1 (all plugins updataed)

The Reverse Proxy configuration:

root@int-rproxy:/etc/apache2/sites-available# cat build-ci.conf

<IfModule mod_ssl.c>

  <VirtualHost _default_:443>

    ServerAdmin webm...@company.com

    Servername build-ci.company.com

    ServerAlias build-ci-adm.company.com

    AllowEncodedSlashes NoDecode

    ErrorLog ${APACHE_LOG_DIR}/build-ci-error.log

    CustomLog ${APACHE_LOG_DIR}/build-ci-access.log combined

    SSLEngine on

    SSLProxyEngine on

    ProxyRequests Off

    ProxyPreserveHost On

    SSLCertificateFile      /etc/ssl/entrust/ServerCertificate.crt

    SSLCertificateKeyFile /etc/ssl/private/comp-rproxy.key

    SSLCertificateChainFile /etc/ssl/entrust/Intermediate.crt

    # Using self-signed certificate on build-ci-app

    SSLProxyCheckPeerName off

    SSLProxyCheckPeerCN off

    SSLProxyVerify none

    BrowserMatch "MSIE [2-6]" \

      nokeepalive ssl-unclean-shutdown \

      downgrade-1.0 force-response-1.0

    ProxyPass / https://build-ci-app.company.com:8443/

    ProxyPassReverse / https://build-ci-app.company.com:8443/

</VirtualHost>

<VirtualHost *:80>

    RewriteEngine On

    ServerName build-ci-adm.company.com

    RewriteEngine On

    RewriteCond %{HTTPS} off

    RewriteRule (.*) https://%{HTTP_HOST}%{REQUEST_URI}

</VirtualHost>

</IfModule>