Nginx reverse proxy to Yesod forwarded ip address does not work

Question

I have nginx set up as a reverse proxy for Yesod. The IP address in /var/log/nginx/access.log is the real IP address of the client.

123.123.123.123 - - [09/Oct/2020:07:11:16 +0000] "GET / HTTP/1.1" 200 ...

But the IP address shown in the log by Yesod is 127.0.0.1, from nginx.

127.0.0.1 - - [09/Oct/2020:07:11:16 +0000] "GET / HTTP/1.0" 200 - "https://...

Here is my nginx configuration:

... 
server {

        server_name example.com;

        location / { 

            proxy_set_header X-Real-IP $remote_addr;
            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
            proxy_set_header Host $http_host;
            proxy_set_header X-NginX-Proxy true;

            proxy_pass http://127.0.0.1:3000; # Reverse proxy to your Yesod app 
        }   

    listen [::]:443 ssl ipv6only=on; # managed by Certbot
    listen 443 ssl; # managed by Certbot
    ssl_certificate /etc/letsencrypt/live/example.com/fullchain.pem; # managed by Certbot
    ssl_certificate_key /etc/letsencrypt/live/example.com/privkey.pem; # managed by Certbot
    include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
    ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot

}
...

I have restarted nginx and the yesod binary. But the IP listed by Yesod is still 127.0.0.1.

What configuration mistake have I made?

Or do I need to edit the logging code of my Yesod binary?

Thank you kind readers

Answer 1

The answer was that there is a configuration option for Yesod to use the forwarded IP headers.

I found it by reading src/Settings.hs which contains this:

data AppSettings = AppSettings
    { appStaticDir              :: String
    -- ^ Directory from which to serve static files.
    , appDatabaseConf           :: PostgresConf
    -- ^ Configuration settings for accessing the database.
    , appRoot                   :: Maybe Text
    -- ^ Base for all generated URLs. If @Nothing@, determined
    -- from the request headers.
    , appHost                   :: HostPreference
    -- ^ Host/interface the server should bind to.
    , appPort                   :: Int
    -- ^ Port to listen on
    , appIpFromHeader           :: Bool
    -- ^ Get the IP address from the header when logging. Useful when sitting
    -- behind a reverse proxy.
...

So you need to either edit config/settings.yaml which contains the line:

...
ip-from-header: "_env:YESOD_IP_FROM_HEADER:false" 
...

Or, you can also change the environment variable running this command export YESOD_IP_FROM_HEADER=true .

That solved it.