Nginx rewrite based on header value

Question

I have a nginx.conf which basically looks like (unnecessary parts omitted):

upstream app {
    server unix:/tmp/unicorn.myapp.sock fail_timeout=0;
}

server {
    listen 80;

    location @app {
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header Host $http_host;
        proxy_redirect off;
        proxy_pass http://app;
    }
}

I want to configure nginx so that the value of a specific header is used to rewrite the url being passed to the upstream.

For example, let's assume that I have a request to /test with the header Accept: application/vnd.demo.v1+json. I'd like it to be redirected to the upstream URL /v1/test, i.e. basically the upstream app will receive the request /v1/test without the header.

Similarly, the request to /test and the header Accept: application/vnd.demo.v2+json should be redirected to the upstream URL /v2/test.

Is this feasible? I've looked into the IfIsEvil nginx module, but the many warnings in there made me hesitant to use it.

Thanks,

r.

edit

In case there's no match, I'd like to return a 412 Precondition Failed immediately from nginx.

Alexey Ten · Accepted Answer · 2014-08-25 06:57:17Z

5

If Accept header does not contain required header return error.

map $http_accept $version {
    default "";
    "~application/vnd\.demo\.v2\+json" "v2";
    "~application/vnd\.demo\.v1\+json" "v1";
}

server {

    location @app {
        if ($version = "") {
            return 412;
        }
        ...;
        proxy_pass http://app/$version$uri$is_args$args;
    }
}

edited Aug 25, 2014 at 6:57

answered Aug 22, 2014 at 6:40

Alexey Ten

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4 Comments

ostinelli Over a year ago

Thank you for your input. You're right I didn't specify it (I've edited the original question). Is there a way to directly return a 412 Precondition Failed in case the header does not contain any matching type?

Alexey Ten Over a year ago

You could set default to something else and use if to check variable value.

ostinelli Over a year ago

Thank you, even though I'm a little allergic to if statements after all the warnings that are on the official docs ^^_

Alexey Ten Over a year ago

> There are cases where you simply cannot avoid using an if, for example if you need to test a variable which has no equivalent directive.

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