Breaking Changes in openHAB 3

openHAB 3 removed deprecated features and concepts in order to clean up the code base and simplify the overall architecture to also have less confusion for users on how to do stuff.

This clearly led to incompatibilities to openHAB 2 setups - this is simply unavoidable for the stated goals.

This page is meant to collect the breaking changes that users should be aware of when (or better before) switching from openHAB 2 to 3.

Breaking Changes for Users

• The runtime now requires Java 11 instead of Java 8, so please make sure to install an appropriate JVM.
• Most visible change is the new UI, which comes with a setup wizard and which replaces Paper UI and HABmin and also serves as a very powerful end-user UI.
• The next-gen rule engine (NGRE) of openHAB 2.5 has now become the official rule engine within openHAB. Good news is that your rule DSL files are not impacted by this change and should run smoothly on it. The only change you’ll have to look out for in your rules is the fact that rules now use Java Time API instead of Jodatime, so some expressions need to be slightly adapted.
• The compatibility layer is gone, so 1.x add-ons will no longer work. If you rely on them and there isn't a new add-on in openHAB 3 for it (yet), you can make use of the new "remote openHAB" binding, which allows to keep an old openHAB 2 instance running with the required add-ons and include it into an openHAB 3 setup.
• The admininstration-related parts of the REST API are now secured, which eliminates many potential attacks from malware in the local network. As a side-effect, some inofficial/custom 3rd party integrations might not work anymore as expected.
• The "Embedded broker" (Moquette) add-on has been removed due to Moquette being an abandoned project with majors bugs that won't be fixed anymore. Please use a separate MQTT broker like Mosquitto instead.
• The updated rrd4j persistence service got changed default database setups. Users of the default database setup of rrd4j Version 1 should note the changed setup for the now three different defaults. By the further use of rrd4j with no custom database setup the history would be lost! In order to keep the history a custom setup, using the former default settings, is needed.
• The new Zoneminder binding in openHAB 3 is no longer compatible with Zoneminder versions earlier than 1.34.0.

Breaking Changes for Developers

Cleaning the code base also means quite some changes for developers. In this section, the most important changes are listed: