nginx does not automatically pick up dns changes in swarm

Thanks to @Moema's pointer I've come up with a solution to this. The default configuration of lets-nginx needs to be tweaked as follows to make nginx pick up IP changes:

  resolver 127.0.0.11 ipv6=off valid=10s;  set $upstream http://${UPSTREAM};  proxy_pass $upstream;

This uses docker swarm's resolver with a TTL and sets a variable, forcing nginx to refresh name lookups in the swarm.

Remember that when you use set you need to generate the entire URL by yourself.

I was using nginx in a compose to proxy a zuul gateway :

        location /api/v1/ {           proxy_set_header X-Forwarded-Host $host:$server_port;           proxy_pass http://rs-gateway:9030/api/v1/;        }        location /zuul/api/v1/ {           proxy_set_header X-Forwarded-Host $host:$server_port;           proxy_pass http://rs-gateway:9030/zuul/api/v1/;        }

Now with Swarm it looks like that :

        location ~ ^(/zuul)?/api/v1/(.*)$ {            set $upstream http://rs-gateway:9030$1/api/v1/$2$is_args$args;            proxy_pass $upstream;            # Set headers            proxy_set_header X-Forwarded-Host $host:$server_port;            proxy_set_header Host $host;            proxy_set_header X-Forwarded-For $remote_addr;            proxy_set_header X-Forwarded-Proto $scheme;            proxy_set_header Upgrade $http_upgrade;            proxy_set_header Connection $http_connection;        }

Regex are good but don't forget to insert GET params into the generated URL by yourself.