| [cosmos-dev] Answers to SDD questions re: "use" and "undoConfig" |
Here are answers to questions that came up in the SDD runtime meeting on Tuesday regarding the purpose and meaning of the "use" operation and the reason for the lack of an "undoConfig" artifact and operation.
The "use" operation indicates that the associated element applies to runtime use of the resource(s). For example, if a requirement includes "use" in its list of operations, the requirement applies at runtime. If "use" is the only operation in the requirements list, the requirement does not apply during deployment. By defining a requirement with "use" as the only supported operation, you provide important information to the user about what they will need to run the deployed software without preventing the deployment. A runtime could check this type of requirement and alert the user if it is not met, without impacting the deployment.
SDD does not include an undoConfig artifact. This does not mean that SDDs would not participate in the undoing on configuration. Undoing configuration implies returning the system to a previous state. The previous state is not something the SDD author can know. If software involved in deployment supports undo of configuration, the action of undoing the configuration would essentially be to configure the system to return it to its previous state. The config operation would be used in this case. For example, before configuration is performed, software might create a configuration artifact using the current state and create an SDD with a ConfigurationUnit and a ConfigArtifact. This could be used at a later date to undo the configuration. This is a similar process to what is sometimes done for install, i.e. an uninstall program specific to the installation is created at installation time and made available in a well-known way.
Julia McCarthy
Install Strategy and Development
julia@xxxxxxxxxx
877-261-0391