load balancing often fails

[seqwait]

i have 2 swarm node

ntr276c3lbdmt58zjrwdfy606    java1    Ready     Active         Leader           20.10.11
d0thnr145hhppyaxx2ku00lnx    java2    Ready     Active                          20.10.11

network: overall_java overlay swarm
java1/java2 [global mode]: springboot(app port 8080) project use overall_java network

nginx not in swarm node ,the config:

upstream app-server {
    server node1.ip:8080 weight=1;
}

server {
    listen 80 ;
    server_name aa888.com www.aa888.com;
    location / {
        proxy_pass http://app-server;
        proxy_read_timeout      7200;
        proxy_connect_timeout   5;
        proxy_set_header        Host                $Host;
        proxy_set_header        X-Forwarded-For     $remote_addr;
    }
}

Every once in a while about 10 minute batch Nginx error timeout log, i don't know What's the problem
upstream timed out (110: Connection timed out) while connecting to upstream, client: upstream timed out (110: Connection timed out) while connecting to upstream, client

[wille]

You cannot use upstream directives in this context. Instead, you will need to keep the upstream hostname in a variable so it's resolved each time nginx tries to use proxy_pass.
You also need to tell nginx to use the default docker resolver, the dns records it sends out should have a proper TTL but I got it working by using a small explicit TTL

The following changes to your config will allow nginx to always find new tasks as you scale up and down.

resolver 127.0.0.1 ttl=5s;
location / {
  set $s tasks.target:80
  proxy_pass http://$s;
}

Sadly, this does not support upstream keepalive directives yet. Only nginx plus supports upstreams with dynamic A records