nginx-proxy hitting "Too many open files" at ~1024 FDs

[welkinwong]

the nginx worker_rlimit_nofile default is 1024

nginx.1     | 2025/11/29 08:46:52 [alert] 23#23: *1369 socket() failed (24: Too many open files) while connecting to upstream,
nginx.1     | 2025/11/29 08:46:52 [crit] 22#22: accept4() failed (24: Too many open files)

access my site will be server error（code 500）😭

[welkinwong]

I temporarily resolved the issue by modifying the Docker daemon's ExecStart parameter:
ExecStart=/usr/bin/dockerd ... --default-ulimit nofile=65535:65535

Through research, I learned that when concurrency exceeds 1024, both the nginx reverse proxy container and the application container are prone to such issues. This can generally be fixed by adding --ulimit nofile=65536:65536 when starting containers. However, for mup's nginx configuration, there's no option to add runtime parameters.