Change Host header in nginx reverse proxy

Question

I am running nginx as reverse proxy for the site example.com to loadbalance a ruby application running in backend server. I have the following proxy_set_header field in nginx which will pass host headers to backend ruby. This is required by ruby app to identify the subdomain names.

location / {
    proxy_pass http://rubyapp.com;
    proxy_set_header Host $http_host;
}

Now I want to create an alias beta.example.com, but the host header passed to backend should still be www.example.com otherwise the ruby application will reject the requests. So I want something similar to below inside location directive.

if ($http_host = "beta.example.com") {
    proxy_pass http://rubyapp.com;
    proxy_set_header Host www.example.com;
}

What is the best way to do this?

This is more appropriate for Server Fault.

Didi Kohen
– Didi Kohen

2013-01-16 06:46:51 +00:00
Commented Jan 16, 2013 at 6:46 — Didi Kohen
– Didi Kohen, Commented Jan 16, 2013 at 6:46

Michał Kupisiński · Accepted Answer · 2013-01-16 07:03:31Z

44

You cannot use proxy_pass in if block, so I suggest to do something like this before setting proxy header:

set $my_host $http_host;
if ($http_host = "beta.example.com") {
  set $my_host "www.example.com";
}

And now you can just use proxy_pass and proxy_set_header without if block:

location / {
  proxy_pass http://rubyapp.com;
  proxy_set_header Host $my_host;
}

answered Jan 16, 2013 at 7:03

Michał Kupisiński

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2 Comments

Dimitri Kopriwa Over a year ago

In what scope should I write the if statement ? server or location ?

re-gor Over a year ago

It should be mentioned, that this directive can be used only once for the header on the current level due to the documentation. > proxy_set_header Allows redefining or appending fields to the request header passed to the proxied server. ... directives are inherited from the previous configuration level if and only if there are no proxy_set_header directives defined on the current level

Bernard Rosset · Accepted Answer · 2020-06-17 16:24:54Z

35

map is better than set + if.

map $http_host $served_host {
    default $http_host;
    beta.example.com www.example.com;
}

server {
    [...]

    location / {
        proxy_pass http://rubyapp.com;
        proxy_set_header Host $served_host;
    }
}

edited Jun 17, 2020 at 16:24

answered Apr 4, 2016 at 16:01

Bernard Rosset

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2 Comments

Ethan Over a year ago

In nginx docs, it's mentioned that set and if are fine if not in the location, but within the server. However, map is also a good alternative.

Bernard Rosset Over a year ago

Could you source the docs you mention? I never read that. Moreover, tickets for nginx involving if often points out trouble related to their use. For instance: #1383. Advice to avoid set & if still stands.

TomCZ · Accepted Answer · 2018-06-28 10:24:28Z

5

Just a small tip. Sometimes you may need to use X-Forwarded-Host instead of Host header. That was my case where Host header worked but only for standard HTTP port 80. If the app was exposed on non-standard port, then this port was lost when the app generated redirects. So finally what worked for me was:

proxy_set_header X-Forwarded-Host $http_host;

answered Jun 28, 2018 at 10:24

TomCZ

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Comments

ricardorover · Accepted Answer · 2019-01-30 16:42:24Z

4

I was trying to solve the same situation, but with uwsgi_pass.

After some research, I figured out that, in this scenario, it's required to:

uwsgi_param HTTP_HOST $my_host;

Hope it helps someone else.

answered Jan 30, 2019 at 16:42

ricardorover

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1 Comment

emyller Over a year ago

This is exactly what I was looking for, thanks so much!

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