Thank you for the reply!

When I wasn't adding lighttpd-module-fastcgi, it definitely was not including it in the build.

The lighttpd-module-fastcgi package is created (unconditionally) when the lighttpd recipe is built (you can verify by checking the installable packages under tmp/deploy/ after building lighttpd).

However, since nothing in the default images has a runtime dependency on lighttpd-module-fastcgi, that package will only be included in the rootfs if you manually add it (e.g. by adding to CORE_IMAGE_EXTRA_INSTALL, as you have done).

ie you need to make the distinction between "is this package being built" and "is this package being included in the rootfs when the image is built".

I have the lighttpd.conf file set up use mod_fastcgi, and without lighttpd-module-fastcgi in my local.conf file, lighttpd would fail to start on the embedded build, complaining that it could not find the fastcgi module. In fact, the same thing happens with php-cgi. I can't find anyplace in any of the layers that I'm using that actually references php-cgi as a package or option, but unless I add it to local.conf using EXTRA_CORE_IMAGES_INSTALL, it doesn't get included in the build.

It's a similar story with the php-cgi package. It's created (unconditionally) when the php recipe is built, but will not be installed in the rootfs unless you add it to your image.

The reason you don't find a direct reference to the string "php-cgi" anywhere is because the php recipe defines it's list of packages in terms of the "${PN}" variable. So the php recipe contains references to "${PN}-cgi" but rather than "php-cgi".