I know how to create a custom 502 page for an upstream error and did it without problems many times, however in this particular case where one proxied response is passed to another proxy I can't find correct config.
General workflow looks like this: user requests a thumbnail of picture, nginx proxies this request to picture storage. If storage returns 404, then nginx proxies this request to app server that generates a thumbnail with requested URI and returns it with code 200, which is passed to user via nginx.
However, if user requests a thumbnail of completely non-existent picture, the app server returns 502. I'd like to display a custom page in this case instead of built-in nginx "502 Bad Gateway".
As i mentioned in the beginning, I know how to create custom 502 page, but I think this particular complex setup with double proxying requires some extra configuration which I can't find :( I've tried a location with internal option, I've tried a location with direct URL to html page and I've tried "@" localtion, but nginx always displayed its built-in page. Both files 502.html and 502x.html exist in /var/www/html and are readable by nginx:
ll /var/www/html total 20 drwxr-xr-x 2 root root 4096 May 3 11:21 ./ drwxr-xr-x 4 root root 4096 Mar 24 11:50 ../ -rw-r--r-- 1 root root 36 Apr 28 10:49 502.html -rw-r--r-- 1 root root 36 May 3 11:21 502x.html Nginx config:
server { listen 443 ssl http2; server_name cdn.domain.tld; ssl_certificate /etc/letsencrypt/live/cdn.domain.tld/fullchain.pem; ssl_certificate_key /etc/letsencrypt/live/cdn.domain.tld/privkey.pem; client_max_body_size 10m; client_body_buffer_size 128k; proxy_connect_timeout 75; proxy_send_timeout 300; proxy_read_timeout 500; proxy_buffer_size 4k; proxy_buffers 4 32k; proxy_busy_buffers_size 64k; proxy_temp_file_write_size 64k; proxy_http_version 1.1; proxy_buffering on; proxy_redirect off; proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for; proxy_set_header X-Forwarded-Proto $scheme; #locations for redirection of 502 response received from thumbnail generator. Not working :( #error_page 502 @502; #error_page 502 https://cdn.domain.tld/502x.html; error_page 502 /502.html; location =/502.html { root /var/www/html; internal; } location @502 { root /var/www/html; try_files /502x.html 502; } location = /502x.html { root /var/www/html; index 502x.html; } location / { proxy_pass http://192.168.10.5/thumbs$request_uri; #Sets caching time for different response codes. If only caching time is specified then only 200, 301, and 302 responses are cached. proxy_cache_valid 30m; add_header X-Proxy-Thumbs-Cache $upstream_cache_status; #intercept 404 from backend #from nginx docs: #If an error response is processed by a proxied server or a FastCGI/uwsgi/SCGI/gRPC server,. #and the server may return different response codes (e.g., 200, 302, 401 or 404), it is possible to respond with the code it returns (equal sign does that) #So we proxy 404 to app which generates thumbnail and returns it with 200 code proxy_intercept_errors on; error_page 404 = @not-found; access_log /var/log/nginx/cdn.access.log cachelog; error_log /var/log/nginx/cdn.error.log; } location @not-found { proxy_pass http://192.168.10.12/thumbgen?key=$request_uri; add_header X-Proxy-Thumbs-Cache2 $upstream_cache_status; proxy_intercept_errors on; access_log /var/log/nginx/cdn-404.access.log cachelog; error_log /var/log/nginx/cdn-404.error.log; } }
