defer binder connection

[vabarbosa]

Changes

this is a first step in alleviating the load on mybinder. additional investigation is underway to further minimize the load and also find alternative solutions.

previously whenever a page loaded, the application would connect to mybinder, execute some init code, then wait for user to run the code cells. this results in a lot of connections and code executions in mybinder given all the times users visit a page and do not try to run any code cells.

this PR modifies the behavior and defers the connection to mybinder until the user has actually tried to execute one of the code cells. unfortunately, this may mean a longer wait when a user is first executing a code cell but that trade-off is acceptable in the immediate term.

related #751

Preview Link

Implementation details

• remove the initializing of mybinder and running of init code from the CodeOutput's mounted() lifecycle
• when user run a code cell
  • check if kernel is available
  • if kernel does not exist, initialize mybinder and run init code then run the code cell
  • if kernel already exists just run the code cell
• update the label of the run to Start kernel and run if no kernel is detected, else keep as Run

How to read this PR

• review changes to logic for initialize kernel in CodeOutput
• review changes to code cell buttons behavior and labeling in ExerciseActionsBar
• review changes to how CodeExercise and Scratchpad interact with updated CodeOutput and ExerciseActionsBar
• visit the preview link and navigate to different pages verifying mybinder is not initialized until you run a code cell

Screenshots

Screen.Recording.2023-06-21.at.00.59.21.mov

[abdonrd]

Looks good, thanks @vabarbosa! 👏