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Summary: Varnish is a state-of-the-art, high-performance HTTP accelerator


Varnish is a webcache & http accelerator. Varnish will either serve cached content, or retireve content from the server, and cache it. Varnish will reduce I/O pressure from webservers.



Install Varnish:

# emerge www-servers/varnish


Configuration is controlled by /etc/varnish/default.vcl & /etc/conf.d/varnishd

/etc/varnish/default.vcl: varnish configuration file
vcl 4.0;
backend default {
    .host = "";
    .port = "8080";
/etc/conf.d/varnishd: varnish configuration file
VARNISHD_OPTS="${VARNISHD_OPTS} -u varnish -g varnish"

Varnish will fetch data from localhost:8080 and serve accelerated proxy data on localhost:80


For 10,000 concurrent connections (or not) a few configuration settings control the power of varnish. If you're having varnish directly serve to the outside world, dial back concurrency to say 50 or 100 connections per ip. You must take into account corporations, and universities hammering several connections from a singular ip. c10k is useful information for if varnish is behind a load balancer such as pound, nginx, or tengine, and all requests are internal and local.

/etc/conf.d/varnishd: varnish concurrency settings
VARNISHD_OPTS="-a -p thread_pool_min=20 -p thread_pool_max=1000 -p thread_pool_add_delay=2 -s malloc,700M"
/etc/varnish/default.vcl: varnish concurrency settings
backend default {
    .host = "";
    .port = "8080";
    .connect_timeout = 600s;
    .first_byte_timeout = 600s;
    .between_bytes_timeout = 600s;
    .max_connections = 10000;
    # .port = "80" led to issues with competing for the port with apache.


To start varnish immediately:

# rc-service varnishd start

To start varnish at boot:

# rc-update add varnishd default


To verify that your traffic is going through varnish.

$ curl -I


If your system has apache installed apache benchmark can show the power of varnish. The examples shown are running 500 requests with concurrency of 100 hits.

ab against a 3 worker cluster mode puma server

# ab -n 500 -c 100 | grep Request

Requests per second: 110.92 [#/sec] (mean)

ab against the same server served through varnish

# ab -n 500 -c 100 | grep Request

Requests per second: 10268.42 [#/sec] (mean)

SSL support

Varnish does not support ssl. There are packages to get around this limitation: