How to handle NGINX Server Load balancer 404 errors in Linux

Use NGINX to achieve load balancing, but the data of a group of servers is not synchronized. It takes some time for the master server to synchronize data to other servers before upstream image.stream.com {server 192.168.1.25: 8088; server 192.168.1.24: 8088; server 192.168.1.23: 8088;} when the user www.2cto.com accesses the image, there is a 60% probability that the file cannot be found. question: How to configure it to the following functions: 1. when I connect to the image server, if the browsing machine is unavailable on the 24th and 23th, I will select another 25 by default?
Solution:
Proxy_next_upstream error timeout invalid_header http_500 http_503 http_404;
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