Running OpenPLC without a Webserver
OpenPLC normally runs with and integrated web server and is perhaps one of the defining characteristics of OpenPLC. The webserver makes deploying new applications and new versions of applications straightforward. For many applications, it is a simple way to get your application running.
Other applications may have no use for the web server and the web server therefore represents an unnecessary and undesired attack surface.
In prior versions of OpenPLC, the webserver was essential. Not only was it a means to change and monitor an application, it also served the purpose of configuring the application at runtime, for example, starting the Modbus server.
Recent changes to OpenPLC have eliminated that limitation, and the purpose of this post is to describe the changes that were made to OpenPLC to enable running in a standalone mode without the webserver.