Nginx map - use variable multiple times or use multiple variables

[Maxim Dounin]

Hello!

On Thu, Dec 05, 2019 at 01:12:07PM -0500, stmx38 wrote:

> Hello,
> 
> We use Nginx map module to sent traffic to different upstreams based on the
> HTTP header:
> 
> map $http_flow $flow_upstream {
>   default "http://flow-dev";
>   prod    "http://flow-prod";
>   test    "http://flow-test";
>   dev     "http://flow-dev";
> }
> 
>   location / {
>     proxy_read_timeout 5s;
>     proxy_pass $flow_upstream;
>   }
> 
> Now, we want to define a different timeouts to different flows:
> 
> map $http_flow $read_timeout {
>   default 15s;
>   prod    5s;
>   test    10s;
>   dev     15s;
> }
> 
>   location / {
>     proxy_read_timeout $read_timeout;
>     proxy_pass $flow_upstream;
>   }
> 
> Bunt Nginx config test show the error here:
> nginx -t
> nginx: [emerg] "proxy_send_timeout" directive invalid value in
> /etc/nginx/conf.d/flow.conf:19
> nginx: configuration file /etc/nginx/nginx.conf test failed

The proxy_send_timeout does not support variables.  Note that if a 
particular directive supports variables, this is explicitly said 
in the documentation.

Instead, consider handling requests in different locations if you 
want to use different configurations for them.  For example:

     map $http_flow $flow {
         default    dev;
         test       test;
     }

     location / {
         rewrite (.*) /$flow/$1 last;
     }

     location /dev/ {
         proxy_pass http://flow-dev/;
         proxy_send_timeout 15s;
     }

     location /test/ {
         proxy_pass http://flow-test/;
         proxy_send_timeout 10s;
     }

(Untested, and might require additional configuration to work 
properly, such as switching off proxy_redirect.)

-- 
Maxim Dounin
http://mdounin.ru/