apxs – APache eXtenSion tool
apxs is a tool for building and installing extension modules for the Apache HyperText Transfer Protocol (HTTP) server. This is achieved by building a dynamic shared object (DSO) from one or more source or object files which then can be loaded into the Apache server under runtime via the LoadModule directive from mod_so.
So to use this extension mechanism your platform has to support the DSO feature and your Apache httpd binary has to be built with the mod_so module. The apxs tool automatically complains if this is not the case. You can check this yourself by manually running the command
# httpd -l