How upgrade instance one by one while upgrading rancher service

I deployed a web app in a rancher service and started several instance, when upgrade the rancher service, the next instance will start to stop and the previous are still initiating.

For example, If i started two instance in a service, all of instance can’t provide service while rancher service upgrading. because the first instance are initiating and the other one was stopped.

So, how can i upgrade the instance one by one when upgrade the service ?

ps: the fowlloing method does’t work

I mitigate this by setting the batch interval to a value high enough for the initialization to complete.

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