When implementing Server-Sent Events behind Nginx, several critical configuration requirements emerge:

# Common pitfalls in default Nginx config
location /events {
    proxy_pass http://backend;
    # Missing crucial SSE-specific directives
}

These directives form the foundation for proper SSE proxying:

location /sse-endpoint {
    proxy_pass http://your_upstream_server;
    proxy_http_version 1.1;
    proxy_set_header Connection '';
    proxy_buffering off;
    proxy_cache off;
    chunked_transfer_encoding off;
    
    # Timeout configuration (adjust as needed)
    proxy_read_timeout 24h;
    proxy_send_timeout 24h;
}

For high-performance SSE implementations:

http {
    upstream backend {
        server 127.0.0.1:8080;
        keepalive 100; # Maintains persistent connections
    }
    
    server {
        location /stream {
            proxy_http_version 1.1;
            proxy_set_header Connection "";
            proxy_pass http://backend;
            # Other SSE directives...
        }
    }
}

Here's a battle-tested configuration used in production environments:

server {
    listen 443 ssl http2;
    server_name yourdomain.com;

    location /api/events {
        proxy_pass http://event_backend;
        proxy_http_version 1.1;
        proxy_set_header Connection '';
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        
        proxy_buffering off;
        proxy_cache off;
        
        # Important timeout settings
        proxy_connect_timeout 7d;
        proxy_read_timeout 7d;
        proxy_send_timeout 7d;
        
        # Additional security headers
        add_header X-Accel-Buffering no;
    }
}

When debugging SSE problems with Nginx:

1. Connection drops: Verify proxy_read_timeout is sufficiently long
2. Buffering problems: Ensure proxy_buffering off is set
3. HTTP/2 issues: Test with both HTTP/1.1 and HTTP/2

For specialized use cases:

# For load balanced environments
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header Host $host;

# For websocket-style behavior with SSE
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection "upgrade";

# For CORS support
add_header 'Access-Control-Allow-Origin' '*';
add_header 'Access-Control-Allow-Methods' 'GET';
add_header 'Access-Control-Allow-Headers' 'Content-Type';

Key metrics to monitor:

• Connection churn rate
• Memory usage per SSE connection
• Proxy worker process load

For high-scale implementations, consider:

events {
    worker_connections 4096; # Increase for many SSE connections
}

http {
    # Reduce I/O operations
    aio threads;
    directio 4k;
}

When implementing Server-Sent Events through Nginx, several critical considerations emerge:

• Connection persistence requirements
• Buffering behavior implications
• Timeout configuration nuances
• HTTP version compatibility

Here's the minimum viable configuration for SSE proxy support:

location /sse-endpoint {
    proxy_pass http://backend;
    proxy_http_version 1.1;
    proxy_set_header Connection '';
    proxy_buffering off;
    proxy_cache off;
    proxy_read_timeout 24h;
}

proxy_http_version 1.1: Mandatory for persistent connections. SSE requires HTTP/1.1 or higher.

Connection header: Empty value prevents connection closure between requests.

Buffering controls: Disabling buffering prevents message aggregation and delays.

For enterprise deployments, consider these enhancements:

location /events/ {
    proxy_pass http://sse_backend;
    proxy_http_version 1.1;
    proxy_set_header Connection '';
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    
    proxy_buffering off;
    proxy_cache off;
    chunked_transfer_encoding off;
    
    proxy_read_timeout 86400s;
    proxy_send_timeout 86400s;
    proxy_connect_timeout 75s;
    
    # SSE-specific headers
    proxy_set_header Accept 'text/event-stream';
    add_header X-Accel-Buffering no;
}

Connection drops: Verify timeout values exceed client expectations. The 24h duration in our example accommodates most use cases.

Message delays: Ensure all buffering mechanisms are disabled, including Nginx's default proxy buffers.

HTTP/2 considerations: While SSE works over HTTP/2, some older clients may require explicit HTTP/1.1 forcing.

For high-volume SSE implementations:

# In main nginx.conf context
worker_processes auto;
events {
    worker_connections 4096;
    use epoll;
    multi_accept on;
}

http {
    # Existing directives...
    
    # SSE-specific optimizations
    proxy_temp_path /dev/shm/nginx_temp;
    client_body_temp_path /dev/shm/nginx_client;
    fastcgi_temp_path /dev/shm/nginx_fastcgi;
}

location ~ ^/secure-events/(.*)$ {
    # Authentication requirements
    auth_request /auth-proxy;
    
    # Standard SSE config
    proxy_pass http://secured_backend/$1;
    proxy_http_version 1.1;
    proxy_set_header Connection '';
    
    # Rate limiting
    limit_req zone=sse burst=20 nodelay;
}