I am trying to proxy a request to different targets depending on an environment variable. My approach was to put the target url into the custom variable $target and give this to proxy_pass.
But using a variable with proxy_pass doesn't seem to work. This simple config leads to a "502 Bad Gateway" response from nginx.
server {
listen 8080;
server_name myhost.example.com;
access_log /var/log/nginx/myhost.access.log;
location /proxy {
set $target http://proxytarget.example.com;
proxy_pass $target;
}
}
The same config without the variable works:
server {
listen 8080;
server_name myhost.example.com;
access_log /var/log/nginx/myhost.access.log;
location /proxy {
proxy_pass http://proxytarget.example.com;
}
}
Is it really not possible to use proxy_pass this way or am I just doing something wrong?
I've recently stumbled upon this need myself and have found that in order to use variables in a proxy_pass destination you need to set a resolver as your error.log would most probably contain something like no resolver defined to resolve ...
The solution in my case was to setup the following using a local DNS for DNS resolution:
location ~ /proxy/(.*) {
resolver 127.0.0.1 [::1];
proxy_pass http://$1;
}
In your case this should work:
location /proxy {
resolver 127.0.0.1 [::1];
set $target http://proxytarget.example.com;
proxy_pass $target;
}
For resolver 127.0.0.1 to work, you need to install bind9 locally. For Debian/Ubuntu:
sudo apt-get install bind9
More information on nginx and dynamic proxy_passing here: http://www.nginx-discovery.com/2011/05/day-51-proxypass-and-resolver.html
Edit: Replaced the previous public DNS with a local one for security issues.
Even though the answer of @soulseekah is complete and correct I want to post an answer for the folks using Nginx inside a cluster of containers, being those inside Kubernetes or Docker Compose.
Basically you have to configure a resolver for Nginx with the address of your actual DNS resolver. For Docker it is always at 127.0.0.11, for Kubernetes refer to this answer
Inside my docker network I was able to successfully configure a dynamic proxy_pass by doing so:
resolver 127.0.0.11 [::1];
set $bcknd http://$http_XBackend$uri$is_args$args;
proxy_pass $bcknd;
Note that it was fundamental to add the $uri$is_args$args since otherwise the proxy pass didn't take in consideration the path and the query string.
PS: in my example, I am reading an header using the $http_XBackend variable. The header is passed by the client as XBackend: host, here the host should be the hostname where you want to forward your calls. I tried using headers with dashes in them with no luck, I had to use an header without dashes.
Edit 16 Jul 2020: Docker doesn't report any more on their webpage the address for the default DNS server. It is still 127.0.0.11:53. If you want to see this value inside your container you need to run cat /etc/resolv.conf.
Stumbled on the same exact issue
proxy_pass wasn't resolving my variables, until we found out our DNS server had a problem
can be checked with this cmd by the way
nslookup your-domain your-dns-ip
location / {
if ($args ~ "^url=(.+)") { #gets the "url" get parameter
set $key1 $1;
proxy_pass $key1;#use the parameter as proxy address
}
}
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8.8.8.8. To prevent DNS spoofing, it is recommended configuring DNS servers in a properly secured trusted local network.resolver kube-dns.kube-system.svc.cluster.local valid=5s;stackoverflow.com/questions/43326913/…