dns name for upstream

[Frank Liu]

Hi,

I saw this example at serverfault.com:

server {
    ...
    resolver 127.0.0.1;
    set $backend "http://dynamic.example.com:80";
    proxy_pass $backend;
    ...
}

I have a few questions:
1) If the resolver DNS becomes unavailable (say connection timeout), what
will nginx do? Will it keep using the old IPs or will it flush the DNS
since TTL expires? If later, the proxy will stop working.
2) In the upstream block, I could define "keepalive #", but with this
example, how can I do that?
3) This page
http://nginx.org/en/docs/stream/ngx_stream_core_module.html#resolver says
"This directive is available as part of our commercial subscription.". Is
that still up to date? Can "resolver", "resolver_timeout" be used in free
edition now?

Thanks!
Frank
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