I have an nginx server (1.10.1) configured that sends requests for PHP files to our PHP tier by directing that traffic via fastcgi_pass to our PHP ELB (AWS's Elastic Load Balancer). We occasionally get outages that a hard stop/start of nginx solves, but are having trouble narrowing the issue down. We believe it is related to DNS resolution, which brings me here. I have a few questions:

1) Does using a variable in fastcgi_pass actually allow the resolver to run, or is it just for proxy_pass as I've seen in 90% of examples?

2) Is this configuration valid? It WORKS, but the resolution doesn't seem to do anything, or I'm not sure how to check that it's updating. The server's resolv.conf points to the same DNS server and uses a search domain so "php:9000" does work:

http {
resolver x.x.x.x valid=10s;

server {
set $phproute "php:9000";

location ~ \.php$ {
include /etc/nginx/fastcgi_params;
fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
fastcgi_pass $phproute;
}
}
}

3) How do I validate that the resolver is working properly outside of waiting for an outage again? Is there a way to get the current cached DNS entries from nginx to compare? I found a tcpdump command, but I'm not really sure what I'm looking at, and it usually gives me no data. Is there a better method?

Thanks in advance. I'm really at a loss here.