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Conditions.
# The Control Panel is implemented so that it initiates the procedure of collecting applications instances resources usage.
# The Controller is implemented so that it stores the list of resources linked to corresponding instances along with resources usage statistics.
# The Control Panel is implemented so that the directories tree rooted in the web site home directory represents the URL structure of the hosting environment as it is accessible from the Internet.
Starting Point. Control Panel requests the Controller to get current usage of a particular resource.
Step 1. The Controller checks its resources storage whether requested resource is present. If the resource is absent, the Controller refuses to continue the operation and returns respective error message. If resource is present the Controller determines instance it belongs to.
Step 2. The Controller parses respective application metadata file APP-META.xml to get the information about the resource script ("//service/provision/resource-script/script-language") and checks if there is an appropriate interpreter in the system and it can be used on the hosting environment to run the script.
Step 3. The Controller invokes the application resource script to get the report.
Sub-step 3.1. Runs the resource script in the environment with respective interpreter.
Sub-step 3.2. If the script invocation succeeds, the Controller checks whether script output can be parsed. If the script invocation fails or script output is not parsed, the Controller returns to Control Panel error message.
Step 4. The Controller parses script output to extract requested resource current usage, updates its storage with new value and passes it to Control Panel.
