Due to creating a separate servlet for eltex-portal service, problems may occur for single-host installations. This is related to the necessity of network reconfiguration for keeping the portal authorization service in working condition. One of the possible solutions is to start a nginx-based proxy server to provide communication via port 8080 "as before".
In this section nginx installation and configuration instructions are given. Necessary changes that should be introduced to tomcat configuration are noted too.

NGINX installation and configuration

NGINX v1.12.2 or higher is required. Detailed installation instructions can be found on the official website: https://nginx.ru/en/linux_packages.html#stable
After installation, add softwlc.conf configuration file to /etc/nginx/conf.d/ directory.

tomcat configuration

open the configuration file
/etc/tomcat7/server.xml

and change the listened port from 8080 to 8081 in Service section:

    <Connector port="8081" protocol="HTTP/1.1"
               connectionTimeout="20000"
               URIEncoding="UTF-8"
               redirectPort="8443" />

add header proxying in Host section:

        <Valve className="org.apache.catalina.valves.RemoteIpValve" 
           remoteIpHeader="X-Forwarded-For" 
           internalProxies="127\.0\.0\.1" 
           requestAttributesEnabled="true"/>

The example of final configuration (commented-out lines are deleted): server.xml

After changing configuration files, restart tomcat to release port 8080 and then nginx to start proxying.
All web servers will continue working as before.