If only have single image option, have a pool of ready and waiting instances mapped for pre-created user names. When new user comes along, grab a username corresponding to instance from the pool of available ones. This will avoid issues with slow startup. When an instance from the pool is used, would be replaced with fresh one so always have spares. This is going to require a process which monitors pool of available instances and use JupyterHub REST API to create user and spawn instances so ready.
If only have single image option, have a pool of ready and waiting instances mapped for pre-created user names. When new user comes along, grab a username corresponding to instance from the pool of available ones. This will avoid issues with slow startup. When an instance from the pool is used, would be replaced with fresh one so always have spares. This is going to require a process which monitors pool of available instances and use JupyterHub REST API to create user and spawn instances so ready.