varnish实现设备检测

原文出处：https://www.varnish-cache.org/docs/3.0/tutorial/devicedetection.html

 

设备检测室根据用户请求的User-Agent来判断返回正确的内容。

 

这样的例子包括对于手机用户这样小屏幕并且高延迟网络发送压缩的文件，或者提供客户端能辨认的流媒体编码格式。

 

有几种策略来处理这样的用户请求：1）redirect到其他的URL. 2) 对于特殊的用户使用不同的后台；3）改变后台的请求以保证后台发送处理过的内容。

 

To make the examples easier to understand, it is assumed in this text that all the req.http.X-UA-Device header is present and unique per client class that content is to be served to.

Setting this header can be as simple as:

sub vcl_recv {
    if (req.http.User-Agent ~ "(?i)iphone" {
        set req.http.X-UA-Device = "mobile-iphone";
    }
}

There are different commercial and free offerings in doing grouping and identifiying clients in further detail than this. For a basic and community based regular expression set, see https://github.com/varnish/varnish-devicedetect/ .

Serve the different content on the same URL

The tricks involved are: 1. Detect the client (pretty simple, just include devicedetect.vcl and call it) 2. Figure out how to signal the backend what client class this is. This includes for example setting a header, changing a header or even changing the backend request URL. 3. Modify any response from the backend to add missing Vary headers, so Varnish' internal handling of this kicks in. 4. Modify output sent to the client so any caches outside our control don't serve the wrong content.

All this while still making sure that we only get 1 cached object per URL per device class.

Example 1: Send HTTP header to backend

The basic case is that Varnish adds the X-UA-Device HTTP header on the backend requests, and the backend mentions in the response Vary header that the content is dependant on this header.

Everything works out of the box from Varnish' perspective.

VCL:

sub vcl_recv {
    # call some detection engine that set req.http.X-UA-Device
}
# req.http.X-UA-Device is copied by Varnish into bereq.http.X-UA-Device

# so, this is a bit conterintuitive. The backend creates content based on
# the normalized User-Agent, but we use Vary on X-UA-Device so Varnish will
# use the same cached object for all U-As that map to the same X-UA-Device.
#
# If the backend does not mention in Vary that it has crafted special
# content based on the User-Agent (==X-UA-Device), add it.
# If your backend does set Vary: User-Agent, you may have to remove that here.
sub vcl_fetch {
    if (req.http.X-UA-Device) {
        if (!beresp.http.Vary) { # no Vary at all
            set beresp.http.Vary = "X-UA-Device";
        } elseif (beresp.http.Vary !~ "X-UA-Device") { # add to existing Vary
            set beresp.http.Vary = beresp.http.Vary + ", X-UA-Device";
        }
    }
    # comment this out if you don't want the client to know your
    # classification
    set beresp.http.X-UA-Device = req.http.X-UA-Device;
}

# to keep any caches in the wild from serving wrong content to client #2
# behind them, we need to transform the Vary on the way out.
sub vcl_deliver {
    if ((req.http.X-UA-Device) && (resp.http.Vary)) {
        set resp.http.Vary = regsub(resp.http.Vary, "X-UA-Device", "User-Agent");
    }
}

Example 2: Normalize the User-Agent string

Another way of signaling the device type is to override or normalize the User-Agent header sent to the backend.

For example

User-Agent: Mozilla/5.0 (Linux; U; Android 2.2; nb-no; HTC Desire Build/FRF91) AppleWebKit/533.1 (KHTML, like Gecko) Version/4.0 Mobile Safari/533.1

becomes:

User-Agent: mobile-android

when seen by the backend.

This works if you don't need the original header for anything on the backend. A possible use for this is for CGI scripts where only a small set of predefined headers are (by default) available for the script.

VCL:

sub vcl_recv {
    # call some detection engine that set req.http.X-UA-Device
}

# override the header before it is sent to the backend
sub vcl_miss { if (req.http.X-UA-Device) { set bereq.http.User-Agent = req.http.X-UA-Device; } }
sub vcl_pass { if (req.http.X-UA-Device) { set bereq.http.User-Agent = req.http.X-UA-Device; } }

# standard Vary handling code from previous examples.
sub vcl_fetch {
    if (req.http.X-UA-Device) {
        if (!beresp.http.Vary) { # no Vary at all
            set beresp.http.Vary = "X-UA-Device";
        } elseif (beresp.http.Vary !~ "X-UA-Device") { # add to existing Vary
            set beresp.http.Vary = beresp.http.Vary + ", X-UA-Device";
        }
    }
    set beresp.http.X-UA-Device = req.http.X-UA-Device;
}
sub vcl_deliver {
    if ((req.http.X-UA-Device) && (resp.http.Vary)) {
        set resp.http.Vary = regsub(resp.http.Vary, "X-UA-Device", "User-Agent");
    }
}

Example 3: Add the device class as a GET query parameter

If everything else fails, you can add the device type as a GET argument.

http://example.com/article/1234.html --> http://example.com/article/1234.html?devicetype=mobile-iphone

The client itself does not see this classification, only the backend request is changed.

VCL:

sub vcl_recv {
    # call some detection engine that set req.http.X-UA-Device
}

sub append_ua {
    if ((req.http.X-UA-Device) && (req.request == "GET")) {
        # if there are existing GET arguments;
        if (req.url ~ "\?") {
            set req.http.X-get-devicetype = "&devicetype=" + req.http.X-UA-Device;
        } else {
            set req.http.X-get-devicetype = "?devicetype=" + req.http.X-UA-Device;
        }
        set req.url = req.url + req.http.X-get-devicetype;
        unset req.http.X-get-devicetype;
    }
}

# do this after vcl_hash, so all Vary-ants can be purged in one go. (avoid ban()ing)
sub vcl_miss { call append_ua; }
sub vcl_pass { call append_ua; }

# Handle redirects, otherwise standard Vary handling code from previous
# examples.
sub vcl_fetch {
    if (req.http.X-UA-Device) {
        if (!beresp.http.Vary) { # no Vary at all
            set beresp.http.Vary = "X-UA-Device";
        } elseif (beresp.http.Vary !~ "X-UA-Device") { # add to existing Vary
            set beresp.http.Vary = beresp.http.Vary + ", X-UA-Device";
        }

        # if the backend returns a redirect (think missing trailing slash),
        # we will potentially show the extra address to the client. we
        # don't want that.  if the backend reorders the get parameters, you
        # may need to be smarter here. (? and & ordering)

        if (beresp.status == 301 || beresp.status == 302 || beresp.status == 303) {
            set beresp.http.location = regsub(beresp.http.location, "[?&]devicetype=.*$", "");
        }
    }
    set beresp.http.X-UA-Device = req.http.X-UA-Device;
}
sub vcl_deliver {
    if ((req.http.X-UA-Device) && (resp.http.Vary)) {
        set resp.http.Vary = regsub(resp.http.Vary, "X-UA-Device", "User-Agent");
    }
}

Different backend for mobile clients

If you have a different backend that serves pages for mobile clients, or any special needs in VCL, you can use the X-UA-Device header like this:

backend mobile {
    .host = "10.0.0.1";
    .port = "80";
}

sub vcl_recv {
    # call some detection engine

    if (req.http.X-UA-Device ~ "^mobile" || req.http.X-UA-device ~ "^tablet") {
        set req.backend = mobile;
    }
}
sub vcl_hash {
    if (req.http.X-UA-Device) {
        hash_data(req.http.X-UA-Device);
    }
}

Redirecting mobile clients

If you want to redirect mobile clients you can use the following snippet.

VCL:

sub vcl_recv {
    # call some detection engine

    if (req.http.X-UA-Device ~ "^mobile" || req.http.X-UA-device ~ "^tablet") {
        error 750 "Moved Temporarily";
    }
}

sub vcl_error {
    if (obj.status == 750) {
        set obj.http.Location = "http://m.example.com" + req.url;
        set obj.status = 302;
        return(deliver);
    }
}