Sling Context-Aware configuration

In the previous blog posting I outlined why there’s a need to store some configuration outside of OSGI and I named Sling Context-Aware Configuration (CA-Config) as a way to implement it.

CA-Config is a relative new feature of AEM (introduced with AEM 6.2) which stores the configuration inside the repository; but besides that it offers some features, which are handy in a lot of usecases:

• You don’t deal with nodes and resources anymore, but only with POJOs. This kind of implementation completly hides where the configuration is stored, but the location of the config is stored as property on the node.
• CA-Config implements an approach based on the repository hierarchy. If a configuration value is not found at the specified config location, the hierarchy is walked towards the root and further configurations are consulted, until a configuration is found or the root node is hit (in that case a default value for the configuration should be used).
• the lookup process is very configurable, although the default one is sufficient in most cases.

A good example for this are content-related settings in a multi-tenant system. Imagine a multi-country and multi-language use-case (where for some countries multiple languages have to be supported); and in each country you should have different user groups, which act as approver in the the content activation process. In the past this was often done by storing it as part of the pages itself, but from a permission point of view it was possible for the authors to change it themselves (which typically only causes trouble). But with CA-Config this can be stored outside of the /content tree in /conf, but closely aligned to the content, and being able to match the weirdest requirements from a structural point of view; that means it is easily possible then have in one country 3 different approver groups for sections of the page, while in another just having 1 group covering all.

Another large usecase are sites, which are based on MSM livecopies. There is always content which is site-specific (e.g. contact adresses, names, logos, etc). And if this content is baked into a”regular” content page which is rolled out by MSM, the blueprint content will always overwrite the content which is specific to the livecopy. With CA-config it is easy possible to maintain these site-specific configurations outside of the regular content tree.

Before CA-Config all of this was implemented for very simple usecases using the InheritanceValueMap, which also implemented such a “walk-up-the-tree-if-the-property-is-not-found” algorithm. But it only looked up the direct parents and did not consider more structured property data as it is possible with CA-Config.

And there were a lot of custom implementations, which created “per site” configuration pages, typically next to the “homepage” page, and restricted access to it via ACLs or dispatcher/webserver/mapping rules. And of course these continue to work, but the access to these configuration data could be managed via the CA-Config as well (depending on the way how the data is stored either by just specifiying these as config path or by a custom lookup logic which can be configured for the CA-Config). And on top of that, these per-site configurations were per-site and not supporting the above mentioned case of having 3 different approver on different parts of the site.

So CA-Config is very flexible and efficient way to retrieve configuration data, which is stored in the repository. But it’s just for retrieving, there’s no prescribed way how the configuration data gets there.
While AEM comes with a configuration editor, it does not support writing the settings for CA-Config (at the moment it’s only designed for editable templates and workflows). WCM.io has a content package for download which allows you to edit these configurations in the authoring UI.

In the next post I will outline how easy it is to actually use CA-Config.