Updating Application Instances

The Controller should implement a mechanism of updating an application instance to the newer version in case that a suitable update package is available. APS supports two types of application updates: patch and upgrade. Generally speaking, the difference is that patching supposes unattended instance update, while upgrading brings more serious changes to the instance and may require the user attendance. Application patch and upgrade are defined in detail by the Specification in section 5.1.15. Updates. Distinguishing patches and upgrades was made with the purpose to facilitate implementation of the Controller update function. Depending on what kind of update is required - patch or upgrade - the Controller behavior slightly differs.

Updating an application instance supposes that the Controller performs the following two steps:

1. Resolving update packages. On this step, the Controller understands that a particular package, or packages, can be used for patching/upgrading the instance.
2. Updating the application instance. This is the very process of update, which supposes that the application of older version is replaced with the one of newer version, and the user settings and files of the old application are picked up by the new one. The Controller's behavior on this step depends on whether the application instance is patched or upgraded and whether a particular update mode is required.

Further in the chapter, we describe what's specific in the Controller implementation about patching and upgrading instances. In case when some information concerns both, we use the terms update and updating.

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