apache Proxy returns random 403 - apache

Question

I'm using 2 VMs configured with Apache2 as a Proxy for the Tomcat server, but I have a very strange behavior I have sometimes HTTP 403 error on my front end, I tried different configurations but I can see that depending on the requests coming from my Load Balancer (plugged with my 2 VMs Apache) it returns HTTP 403 randomly (and not for the same requests as well).
Here is the flow:
Front end -> Load Balancer (443)
-> Apache2 Reverse Proxy (443) -> Tomcat (8080)
-> Apache2 Reverse Proxy (443) -> Tomcat (8080)
I run this Apache2 Reverse Proxy on Ubuntu, here is the configuration for my Apache2 Proxies:
<IfModule mod_ssl.c>
<VirtualHost *:443>
ServerAdmin webmaster#localhost
ErrorLog ${APACHE_LOG_DIR}/error.log
CustomLog ${APACHE_LOG_DIR}/access.log combined
<Proxy *>
AddDefaultCharset Off
Order deny,allow
Allow from all
</Proxy>
Header add Access-Control-Allow-Origin "https://myfrontend.com"
SSLEngine on
SSLCertificateFile /etc/ssl/myfrontend.key
SSLCertificateKeyFile /etc/ssl/privatemyfrontend.key
SSLCertificateChainFile /etc/ssl/ca_bundle
SSLProxyEngine on
ProxyRequests off
SSLProxyVerify require
SSLProxyVerifyDepth 1
SSLProxyCACertificateFile "/etc/ssl/myfrontend.key"
SSLProxyCheckPeerName on
ProxyPreserveHost On
ProxyPass / http://localhost:8080/back/
ProxyPassReverse / http://localhost:8080/back/
</VirtualHost>
any idea why I'm getting such 403 errors?

Answer 1

I had a similar problem with two applications (Gitlab and SonarQube) deployed behind an Apache server configured as a reverse proxy. I solved it by uninstalling the mod_evasive module of Apache.