Weird timeouts, not sure if I've set the right threshholds

[mike]

It is proxying (basically just load balancing) to 3 upstream nginx
webservers which do FastCGI/PHP/normal static files.

I get a lot of "upstream timed out" errors and I can't determine why
exactly. Perhaps my buffers are too high, too low, timeouts are too
high, too low? I bumped up the timeouts on my proxy machine higher
than I normally would set so it wouldn't timeout as often but it still
does. All the machines are quad-core xeons with 4GB RAM, SATA2 disks,
dedicated to web/fastcgi/php, all connected via a private gigabit
VLAN... the files are hosted on NFS, but I'm not seeing any errors
related to that in logs either..


nginx PROXY:

user www-data www-data;
worker_processes 4;
worker_cpu_affinity 0001 0010 0100 1000;
working_directory /var/run;
error_log /var/log/nginx/error.log error;
pid /var/run/nginx.pid;

events {
    worker_connections  1024;
}

http {
    upstream webservers {
        server web01:80;
        server web02:80;
        server web03:80;
    }
    include /etc/nginx/mime.types;
    default_type application/octet-stream;
    sendfile on;
    tcp_nopush on;
    tcp_nodelay on;
    client_max_body_size 100m;
    client_header_buffer_size 8k;
    large_client_header_buffers 12 6k;
    keepalive_timeout 5;
    gzip on;
    gzip_static on;
    gzip_proxied any;
    gzip_min_length 1100;
    #gzip_http_version 1.0;
    gzip_comp_level 2;
    gzip_types text/plain text/html text/css application/x-javascript
text/xml application/xml application/xml+rss
    gzip_disable "MSIE [1-6]\.";
    gzip_vary on;
    server_names_hash_max_size 4096;
    server_names_hash_bucket_size 128;
    server {
        listen 80;
        access_log off;
        location / {
            proxy_pass http://mikehost;
            proxy_next_upstream error timeout http_500 http_503 invalid_header;
            proxy_max_temp_file_size 0;
            proxy_read_timeout 50;
            proxy_connect_timeout 30;
            proxy_set_header Host $host;
            proxy_set_header X-Real-IP $remote_addr;
            proxy_ignore_client_abort on;
        }
    }
}


nginx WEBSERVERS:

user www-data www-data;
worker_processes 4;
worker_cpu_affinity 0001 0010 0100 1000;
working_directory /var/run;
error_log  /var/log/nginx/error.log debug;
pid /var/run/nginx.pid;



events {
    worker_connections  1024;
}

http {
    include       /etc/nginx/mime.types;
    default_type  application/octet-stream;

    set_real_ip_from 10.13.5.16;
    access_log off;
    sendfile on;
    tcp_nopush on;
    tcp_nodelay on;
    client_max_body_size 100m;
    client_header_buffer_size 8k;
    large_client_header_buffers 12 6k;
    keepalive_timeout  5;
    server_tokens off;
    gzip off;
    gzip_static off;
    server_names_hash_max_size 4096;
    server_names_hash_bucket_size 128;

# then an example vhost block
 server {
    listen 80;
    server_name michaelshadle.com www.michaelshadle.com;
    index index.php;
    root /home/mike/web/michaelshadle.com/;
    location ~ .php {
        include /etc/nginx/fastcgi.conf;
        fastcgi_pass 127.0.0.1:11000;
        fastcgi_index index.php;
    }
    if (!-e $request_filename) {
        rewrite ^(.+)$ /wordpress/index.php?q=$1 last;
    }
}


Any thoughts? Would turning off some buffers on the proxy make it
better, or would turning off buffering on the webservers make it
better? Not quite sure here where the best place would be to change
(if anywhere...)

Thanks..