Scale on a schedule

Add schedules to an Auto Scaling Group to change its capacity at times you choose, for example more VMs on weekday mornings and fewer at night. A schedule works on its own with the Scheduled policy, or on top of Usage-based scaling. For usage-based scaling, see Scale on usage.

Before you begin

• An Auto Scaling Group, or the Create Auto Scaling Group form open. See Create an Auto Scaling Group.
• The times you want, converted to UTC.

Choose the policy

In Scaling, choose the Policy:

• Usage-based adds and removes VMs by usage. Schedules are optional. Each schedule sets the minimum the group works above.
• Scheduled changes capacity only at the times you set and ignores usage. It needs at least one schedule. Each run sets the number of VMs to the schedule’s count exactly, up or down.

Switching to Scheduled adds a first, blank schedule for you. Switching back to Usage-based keeps only the schedules that have a time.

Add a schedule

1. In Schedules, select Add a schedule. You can add any number of schedules, named Schedule 1, Schedule 2, and so on.
2. In Runs at, enter the time in cron format, “minute hour day month weekday”. For example, 0 9 * * 1-5 is 9:00 on weekdays. The time is UTC. TIR spells the time out in plain words and gives the next run, so you can check it. Or pick a preset, such as Weekdays at 9 AM, Daily at 12 PM, Daily at 8 PM or Monthly (1st, 12 AM).
3. Set the VM count in “Set the minimum to” (Usage-based) or “Set the VM count to” (Scheduled). The count is at least 1 and at most one less than Maximum VMs. It can be lower than the group’s own minimum, so a night schedule can lower capacity.
4. In Hold it for, choose how long the change lasts. The default is 8 hours.

Each schedule needs a valid time of its own, and two schedules cannot share one.

Choose how long a schedule holds

Hold it for offers 1 hour, 4 hours, 8 hours, 12 hours, 1 day and Until another schedule changes it.

• With a time, the group drops back to its own minimum when the hold ends. A hold lasts at most until the schedule’s next run.
• With Until another schedule changes it, the schedule’s capacity stays until a different schedule replaces it.

How a schedule changes capacity

• On a Usage-based group, a schedule sets the lowest number of VMs the group runs from that time. The group still adds VMs above it when usage rises. The group raises the VM count at once if it is below the schedule’s count. Usage scaling handles any decrease.
• On a Scheduled group, each run sets the number of VMs to the schedule’s count exactly, up or down. It ignores usage.
• When several holds are active, the highest count wins. A Scale Now hold counts as one more.

A schedule runs only while the group is Running. If the group is in another state at that time, for example Stopped, the run is skipped for good, and Scaling Activity records “Scheduled change skipped”.

Edit or remove a schedule

Change schedules from Edit. On Edit Auto Scaling Group, change the time, count or hold of a schedule, or remove it, then select Update Auto Scaling Group. Removing the last schedule of a group that had schedules deletes it when you save. A Scheduled group must keep at least one schedule.

See what the schedules do

The Scaling Activity tab has each schedule with the capacity it sets, how long it holds, and its next run in UTC. A schedule is Enabled, Holding until the time given, or Disabled. For a Scheduled group, Overview also gives the next change.

To add VMs right now instead, see Use Scale Now. For how the pieces fit, see How auto scaling works.