nginx 2,upstream question

[nanaya]

Hi

On Tue, Sep 22, 2015, at 04:59 PM, vps4 wrote:
> i have 2 backend server A & B, i want the upstream only works with A,
> when A
> die then works with B, if A not die , only works with A
> how can i do
> 

this?

upstream backend {
  server A;
  server B backup;
}