curl -D - -s http://app.test.ru/.well-known/acme-challenge/555.txt
2021/11/13 13:07:53 [alert] 41143#41143: *77772 socket() failed (24: Too many open files) while connecting to upstream, client: *.*.18.189, server: app.test.ru, request: "GET /.well-known/acme-challenge/555.txt HTTP/1.0", upstream: "http://*.*.18.189:80/.well-known/acme-challenge/555.txt", host: "lb"
2021/11/13 12:42:09 [error] 40804#40804: *19997 recv() failed (104: Connection reset by peer) while reading response header from upstream, client: *.*.18.189, server: app.test.ru, request: "GET /opt/www/acme/.well-known/acme-challenge/555.txt HTTP/1.0", upstream: "http://*.*.18.189:80/opt/www/acme/.well-known/acme-challenge/555.txt", host: "lb"
2021/11/13 12:45:37 [alert] 40855#40855: *29989 socket() failed (24: Too many open files) while connecting to upstream, client: *.*.18.189, server: app.test.ru, request: "GET /opt/www/acme/.well-known/acme-challenge/555.txt HTTP/1.0", upstream: "http://*.*.18.189:80/opt/www/acme/.well-known/acme-challenge/555.txt", host: "lb"
[13/Nov/2021:11:36:54 +0000] "GET /opt/www/acme/.well-known/acme-challenge/555.txt HTTP/1.1" 404 162 "-" "curl/7.68.0"
user@lb1:/opt/www/acme/.well-known/acme-challenge$ ll
total 8
drwxr-xr-x 2 root root 4096 Nov 13 11:33 ./
drwxr-xr-x 3 root root 4096 Nov 13 11:20 ../
-rw-r--r-- 1 root root 0 Nov 13 11:33 555.txt
user@lb1:/var/log/nginx$ curl -D - -s http://app.test.ru/opt/www/acme/.well-known/acme-challenge/555.txt
2021/11/13 12:04:59 [error] 40173#40173: *3087 recv() failed (104: Connection reset by peer) while reading response header from upstream, client: *.*.*..189, server: app.test.ru, request: "HEAD /opt/www/acme/.well-known/acme-challenge/555.txt HTTP/1.0", upstream: "http://*.*.*.189:80/opt/www/acme/.well-known/acme-challenge/555.txt", host: "lb"
server {
listen 80;
server_name lb2.test.ru;
location /.well-known/acme-challenge {proxy_pass http://lb1.test.ru;}
listen 80.*.*.*:80;
listen 80; listen 443;