When dealing with high-traffic Django deployments using the Gunicorn/Nginx stack with Unix sockets, the "Resource temporarily unavailable" (EAGAIN/EWOULDBLOCK) error typically indicates system resource exhaustion at the OS level. This manifests when Nginx cannot establish new connections to the Gunicorn socket due to:

[error] 2388#0: *208027 connect() to unix:/tmp/gunicorn-ourapp.socket failed (11: Resource temporarily unavailable)

From your setup, several parameters need optimization:

• Worker processes calculation: workers = multiprocessing.cpu_count() * 3 + 1
• Socket connection handling in Nginx
• System-level file descriptor limits

Add these parameters to your gunicorn.conf.py:

backlog = 2048  # Double the default
worker_connections = 1000
keepalive = 5

Then modify your Nginx configuration:

location / {
    proxy_pass http://unix:/tmp/gunicorn-ourapp.socket;
    proxy_socket_keepalive on;
    proxy_http_version 1.1;
    proxy_set_header Connection "";
    proxy_buffers 8 32k;
    proxy_buffer_size 64k;
}

For high-traffic servers, consider these kernel parameter adjustments:

# /etc/sysctl.conf
net.core.somaxconn = 4096
net.ipv4.tcp_max_syn_backlog = 4096
fs.file-max = 2097152

Apply them with:

sudo sysctl -p

Instead of static worker count, consider dynamic scaling:

# gunicorn.conf.py
workers = 4  # Base workers
threads = 2  # Per worker
max_requests = 1000
max_requests_jitter = 50

Add this to your supervisor configuration to ensure proper socket cleanup:

[program:gunicorn]
command=/path/to/gunicorn --config /path/to/gunicorn.conf.py app.wsgi
umask=022
user=youruser
autostart=true
autorestart=true
stopsignal=QUIT
stopasgroup=true
killasgroup=true

Install these tools to monitor socket connections:

sudo apt install lsof net-tools
# Monitor active connections:
watch -n 1 "sudo netstat -anp | grep gunicorn"
# Check file descriptor usage:
watch -n 1 "cat /proc/sys/fs/file-nr"

When running Django with Gunicorn and Nginx via Unix sockets under heavy traffic, the "Resource temporarily unavailable" (EAGAIN) error typically indicates one of these scenarios:

1. Gunicorn worker exhaustion (all workers busy processing requests)
2. OS-level connection queue overflow
3. File descriptor limits being hit
4. Socket buffer capacity issues

The current worker calculation workers = multiprocessing.cpu_count() * 3 + 1 might not be optimal for your traffic pattern. Consider these adjustments:

# New gunicorn.conf.py
import multiprocessing

bind = 'unix:/tmp/gunicorn-ourapp.socket'
workers = multiprocessing.cpu_count() * 2  # More conservative scaling
threads = 2  # Add threaded mode for I/O bound workloads
backlog = 2048  # Increase connection queue
timeout = 300  # Reduced from 600
keepalive = 2  # Enable connection reuse

The current Nginx config needs several critical enhancements:

upstream gunicorn_socket {
    server unix:/tmp/gunicorn-ourapp.socket fail_timeout=0;
    keepalive 32;  # Maintain persistent connections
}

server {
    # ... existing config ...
    
    location / {
        proxy_pass http://gunicorn_socket;
        proxy_http_version 1.1;
        proxy_set_header Connection "";
        proxy_buffers 8 32k;
        proxy_buffer_size 64k;
        
        # Critical timeouts should match Gunicorn
        proxy_read_timeout 300s;
        proxy_connect_timeout 75s;
        
        # Add these important headers
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
    }
}

Even with 50,000 open files limit, you might need deeper OS tuning:

# /etc/sysctl.conf additions
net.core.somaxconn = 4096
net.ipv4.tcp_max_syn_backlog = 4096
net.core.netdev_max_backlog = 4096
fs.file-max = 2097152

# For the socket itself
net.unix.max_dgram_qlen = 4096

Apply with sysctl -p after saving changes.

Use these commands to monitor your bottleneck:

# Check socket connection queue
ss -xlp | grep gunicorn

# Monitor worker utilization
watch -n 1 'ps -ef | grep gunicorn | grep -v grep | wc -l'

# Check for dropped connections
dmesg | grep -i "tcp drop"
netstat -s | grep -i "listen"

For very high traffic, consider these architectural changes:

# Use multiple socket files with load balancing
upstream gunicorn_cluster {
    server unix:/tmp/gunicorn-ourapp-1.socket;
    server unix:/tmp/gunicorn-ourapp-2.socket;
    least_conn;  # Better than round-robin for uneven loads
}

# In Gunicorn config
import glob
sockets = [f'unix:/tmp/gunicorn-ourapp-{i}.socket' for i in range(1,3)]
bind = sockets