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Although Kea offers a lot of flexibility, there may be cases where its behavior needs customisation. To accommodate this possibility, Kea includes the idea of "Hooks". This feature lets Kea load one or more dynamically-linked libraries (known as "hooks libraries") and, at various points in its processing ("hook points"), call functions in them. Those functions perform whatever custom processing is required. Hooks libraries are attached to individual Kea processes, not to Kea as a whole. This means (for example) that it is possible to associate one set of libraries with the DHCP4 server and a different set to the DHCP6 server. Another point to note is that it is possible for a process to load multiple libraries. When processing reaches a hook point, Kea calls the hooks library functions attached to it. If multiple libraries have attached a function to a given hook point, Kea calls all of them, in the order in which the libraries are specified in the configuration file. The order may be important: consult the documentation of the libraries to see if this is the case. The next section describes how to configure hooks libraries. If you are interested in writing your own hooks library, information can be found in the Kea Developer's Guide.

The hooks libraries for a given process are configured using the hooks-libraries keyword in the configuration for that process. (Note that the word "hooks" is plural). The value of the keyword is an array of strings, each string corresponding to a hooks library. For example, to set up two hooks libraries for the DHCPv4 server, the configuration would be: "Dhcp4": { : "hooks-libraries": [ "/opt/charging.so", "/opt/local/notification.so" ] : } At present, the libraries are specified as a simple list. A future version of Kea will support the capability of specifying a set of parameters for each library. When that is added, it is likely that the syntax for specifying hooks libraries will change. Notes: The full path to each library should be given. As noted above, order may be important - consult the documentation for each library. An empty list has the same effect as omitting the hooks-libraries configuration element all together. At the present time, only the kea-dhcp4 and kea-dhcp6 processes support hooks libraries.