juptyerhub-placeholder-autoscaler

Draft of a service to autoscale jupyterhub placeholders

keeps placeholder replica count updated to meet:

• minimum placeholder count
• minimum total capacity (current users + placeholder count)

Reflectors are vendored from kubespawner 0.15. If this code ran in the Hub pod, they could just be imported.

For @yuvipanda

Idea from @manics and @betatim

Event descriptions are searched for lines that look like:

min_placeholders: 10
min_capacity: 100

Only min_capacity and min_placeholders assignments are used, and only integer values are applied.

Configuration

The following environment variables configure the behavior:

• NAMESPACE - the kubernetes namespace in which to look for pods
• PLACEHOLDER_MIN_COUNT - the minimum number of placeholders to have in place, when not overridden by a calendar event
• PLACEHOLDER_MIN_CAPACITY - the minimum total "warm" capacity, taking current active users into account, when not overridden by a calendar event
• PLACEHOLDER_CHECK_INTERVAL - the interval, in seconds, on which to check and update the placeholder count. The calendar, if defined, is fetch each time.
• PLACEHOLDER_ICS_URL - URL for a .ics-format calendar (e.g. a public google calendar link)

Test your calendar

You can test your calendar and see what the placeholder counts will be over time with:

python -m placeholderautoscaler.plan $calendar_url

which will show you each change in the placeholder count due to calendar events.