Setup nginx not to crash if host in upstream is not found

Question

We have several rails apps under common domain in Docker, and we use nginx to direct requests to specific apps.

our_dev_server.com/foo # proxies to foo app
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Answer 1

The main advantage of using upstream is to define a group of servers than can listen on different ports and configure load-balancing and failover between them.

In your case you are only defining 1 primary server per upstream so it must to be up.

Instead, use variables for your proxy_pass(es) and remember to handle the possible errors (404s, 503s) that you might get when a target server is down.