The ingredients of this recipe include the Apache Karaf distribution kit, access to JDK, and Internet connectivity. Generally, you'll also need to perform the steps outlined in the Installing OpenJPA modules in Apache Karaf recipe.
Thanks to Apache Karaf's feature system, installing JTA is a very simple one-step process.
Why do we not have to add the feature URL? This is because Apache Karaf's standard distribution includes the JTA feature URL by default.
karaf@root()> feature:install transaction