use a secondary upstream as backup

[Sergey A. Osokin]

Hi Sébastien,
hope you're doing well.

Thanks for the question.

On Wed, Apr 23, 2025 at 12:07:21PM +0200, Sébastien Rebecchi via nginx wrote:
> backup, meaning NGINX will only use them if all primary servers fail.
> 
> In my case, I have some servers running over HTTP and would like to
> configure HTTPS servers as backups. However, since an upstream can only use
> one protocol, this setup isn't currently possible.

[...]

The solution you may help and you may want to try to implement is "double"
proxy, where:
- at first, nginx is proxy to the loopback upstream, i.e. to itself
- on the second step nginx proxies from loopback to an original upstream

So, the original upstream block will look like this:

upstream insecure {
    server A.B.C.D:80;    # http server
    server 127.0.0.1:8999;

    <other directives here>
}

upstream secure {
    server E.F.G.H:443;    # https

    <other directives here>
}

<other servers here>

server {
    listen 127.0.0.1:8999;

    location / {
        proxy_pass https://secure;

        <other directives here>
    }
}

> Is there a feature like this planned, or one that could be considered for
> future development?

I don't think such feature is planned at the moment, just because all
servers defined in the same upstream should be configured equally.

Hope that helps.
Thank you.

-- 
Sergey A. Osokin