I am running apache-bench targeting a nginx LB which fetches objects from varnish cache.

My ab comand is :
ab -r -k -c 1500 -t 60 -n 10000000 http://abc.xyz.com/150kb.txt


I am getting 502 errors (bad gateway) and below lines in my error logs of nginx reverse proxy. But, if I point directly to varnish, this run smoothly without any errors.

2014/12/11 19:31:48 [error] 30476#0: *1011 no live upstreams while connecting to upstream, client: 10.20.4.12, server: abc.xyz.com, request: "GET /150kb.txt HTTP/1.0", upstream: "http://upstream-abc.xyz.com/150kb.txt", host: "abc.xyz.com"



2014/12/11 19:31:49 [error] 30476#0: *730 connect() failed (110: Connection timed out) while connecting to upstream, client: 10.20.4.12, server: abc.xyz.com, request: "GET /150kb.txt HTTP/1.0", upstream: "http://10.10.0.132:80/150kb.txt", host: "abc.xyz.com"


Below are some information about my nginx server -
Server Config (VM) :
4GB RAM
2 vcpus


Fine tuning parameters in nginx.conf -
proxy_buffer_size 1024k;
proxy_buffers 16 1024k;
proxy_busy_buffers_size 2048k;
large_client_header_buffers 16 2048k;
proxy_max_temp_file_size 2048m;
proxy_temp_file_write_size 2048k;
proxy_connect_timeout 600;
proxy_send_timeout 600;
proxy_read_timeout 600;


sysctl parameters -
net.ipv4.ip_forward = 0
net.ipv4.conf.default.rp_filter = 1
net.ipv4.conf.default.accept_source_route = 0
kernel.sysrq = 0
kernel.core_uses_pid = 1
net.ipv4.tcp_syncookies = 1
net.ipv4.tcp_window_scaling = 1
net.ipv4.tcp_timestamps = 1
net.ipv4.tcp_sack = 1
net.ipv4.tcp_fin_timeout = 30
net.ipv4.tcp_keepalive_intvl = 30
net.ipv4.tcp_keepalive_probes = 5
net.ipv4.tcp_tw_recycle = 1
net.ipv4.tcp_tw_reuse = 0
net.ipv4.tcp_no_metrics_save = 1
net.ipv4.tcp_synack_retries = 1
net.ipv4.tcp_max_orphans = 400000
net.core.netdev_max_backlog = 65535
net.ipv4.ip_local_port_range = 1024 65000
fs.file-max = 10000000
net.core.rmem_max = 16777216
net.core.wmem_max = 16777216
net.ipv4.tcp_rmem = 4096 87380 16777216
net.ipv4.tcp_wmem = 4096 16384 16777216
net.ipv4.tcp_syncookies = 0
net.ipv4.tcp_max_tw_buckets = 400000
net.ipv4.tcp_max_syn_backlog = 20480
net.core.somaxconn = 65535
net.core.optmem_max = 16777216

Can somebody help on the issue please ?

Thanks,

Viral