BUSINESS_FOR_DEVELOPER_TO_KNOW.md

Business logic for developers to know

ALICE's Experiment Control System (ECS) uses entities named environments to enable users to take data in ALICE. These environments are a set of software and hardware configurations used for preparation and during data-taking operations.

Environment States and Transitions

Environments can transition (link) between multiple states. These states can be:

• state machines - link
• virtual states (states that are not real but used for software logic such as DESTROY or PENDING)

Thus, for the GUI to provide a good user experience, the ECS GUI introduces a few logic items that are to be known when developing for ECS GUI:

Deployment and ECS GUI private attributes

A deployment is a set of operations that prepares hardware and software for data taking operations. A deployment is a definition in ECS GUI that covers an environment first transition from:

• PENDING (virtual state) -> STANDBY -> DEPLOY -> CONFIGURED

For this sequence of actions, ECS GUI assigns a private attribute isDeploying and deploymentError to the environment so that it can display to the User all the information needed.

• isDeploying set to:
  • true - only by:
    • the response of the NewEnvironmentAsync
    • the first event from ECS via Kafka of state PENDING
  • false - only if:
    • an event with state CONFIGURED and message 'transition completed successfully' is received
    • an event with an error message is received during when isDeploying is true already (TBD)
• deploymentError is updated every time there is an event with an error (TBD)

These attributes allow the GUI to display all necessary deployment information to the user.

If a deployment fails, the ECS will remove it from the active environments list. Thus, the GUI uses deploymentError to make sure the environment is kept in-memory until the user acknowledges the error.