What is the number of connections from container to container?

Question

linux

4 docker containers were raised on the server: mariadb (the official image from the docker hub), a self-assembly container with nginx as a reversed proxy, and two containers with applications that are accessed from the upstream nginx and proxied.
Today, on one of the containers of the App1 application, at a volume of 500 hits per second, connections to MariaDB began to fall off with an error like "cannot assign requested address", and not 100% of the requests, but some of them (for example, from five refreshes of the script accessing base, every 5 or 6 crashed with a connection error). The second App2 (100rps) worked fine.
Any attempts to look at the current number of active connections in MariaDB showed that it was a quarter lower than the limits set in the database config, and the running App2 only continues to suggest that I ran into some number of active connections per container in App1.
How it is possible to debug such situation and where first of all to look?
Applications are located in a separate docker-compose from the base and nginx, connected by a common network between the composes, calls to the base go by the name of the container.

Answer 1

I think it's worth looking at the number of active container sockets (ip addresses) App1. I have a feeling that you are limited by the maximum number of open ports for outgoing connections.
You can read more here and do the mentioned research https://www.percona.com/blog/2014/12/08/what-happe...