- Updates initiated to Application Gateway are applied one [update domain](../../articles/virtual-machines/availability-set-overview.md#how-do-availability-sets-work) at a time<sup>1</sup>. As each update domain's instances are being updated, the remaining instances in other update domains will continue to serve traffic. Active connections are gracefully drained from the instances being updated for up to 5 minutes to help establish connectivity to instances in a different update domain before the update begins. During update, Application Gateway will temporarily run at reduced max capacity, which is determined by the number of instances configured. The update process will proceed to the next set of instances only if the current set of instances have been upgraded successfully.
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