During the Zope 4 development, several packages that used to be included have been separated out and ship separately.
On this page the term "add to your application buildout" is used generically. How you do so depends on your chosen installation method, like adding an egg name to a requirements file for pip installs, or adding it to an eggs specification for zc.buildout.
ZServer does not support Python 3. The following only applies for Zope 4 under Python 2.
If you want to continue using ZServer instead of moving to WSGI you need to add the ZServer egg to your application buildout.
If you use the recipe plone.recipe.zope2instance in a buildout, add it to its eggs attribute and also add the flag wsgi = off.
If you have used (or want to use) the built-in support for sessioning, add the egg Products.Sessions to your application buildout.
You also need to make sure that your Zope configuration file contains a ZODB configuration for a temporary folder like this:
<zodb_db temporary>
<temporarystorage>
name Temporary database (for sessions)
</temporarystorage>
mount-point /temp_folder
container-class Products.TemporaryFolder.TemporaryContainer
</zodb_db>If you have External Method objects in your ZODB, make sure to add the egg Products.ExternalMethod to your application buildout.
If you have used the Site Error Log (the error_logs objects that show information about errors occurring in your application), add the egg Products.SiteErrorLog to your application buildout.