nginx and blazor - upstream prematurely closed connection - 502 Bad Gateway - nginx

Question

I am trying to deploy a blazor server template app on Nginx, but i'm stucked with this problem.
I tried everything that I could find online, but still the same error.
error.log
*36 upstream prematurely closed connection while reading response header from upstream, client:, server: , request: "GET / HTTP/1.1", upstream: "http://127.0.0.1:7155/"
in case of that helps, browsers just show 502 code
this is my nginx.conf
user www-data;
worker_processes auto;
pid /run/nginx.pid;
include /etc/nginx/modules-enabled/*.conf;
events {
worker_connections 768;
# multi_accept on;
}
http {
##
# Basic Settings
##
sendfile on;
tcp_nopush on;
types_hash_max_size 2048;
# server_tokens off;
# server_names_hash_bucket_size 64;
# server_name_in_redirect off;
include /etc/nginx/mime.types;
default_type application/octet-stream;
##
# SSL Settings
##
ssl_protocols TLSv1 TLSv1.1 TLSv1.2 TLSv1.3; # Dropping SSLv3, ref: POODLE
ssl_prefer_server_ciphers on;
##
# Logging Settings
##
access_log /var/log/nginx/access.log;
error_log /var/log/nginx/error.log;
##
# Gzip Settings
##
gzip on;
##
# Virtual Host Configs
##
include /etc/nginx/conf.d/*.conf;
include /etc/nginx/sites-enabled/*;
}
and here the server block at /sites-enabled/
server {
listen 80;
listen [::]:80;
return 301 https://$host$request_uri;
}
server {
listen 443 ssl http2;
listen [::]:443 ssl http2;
ssl_certificate /etc/nginx/cert.pem;
ssl_certificate_key /etc/nginx/cert.key;
location / {
proxy_pass http://dotnet;
proxy_set_header Host $host;
proxy_http_version 1.1; # you need to set this in order to use params below.
proxy_temp_file_write_size 64k;
proxy_connect_timeout 10080s;
proxy_send_timeout 10080;
proxy_read_timeout 10080;
proxy_buffer_size 64k;
proxy_buffers 16 32k;
proxy_busy_buffers_size 64k;
proxy_redirect off;
proxy_request_buffering off;
proxy_buffering off;
}
}
upstream dotnet {
zone dotnet 64k;
server 127.0.0.1:7155;
}
I don't know what I am doing wrong. please help

Answer 1

Based on this I made some notes on how to deploy on Nginx a Blazor Server App. I share and hope that helps.
Install nginx and start it:
sudo apt-get install nginx
sudo service nginx start
Now you need to configure it so that requests arriving to port 80 are passed to your app on port 5000. To do that, open the /etc/nginx/sites-available/default file in your favorite editor. The default configuration defines only one server, listening on port 80. Under this server, look for the section starting with location /: this is the configuration for the root path on this server. Replace it with the following configuration:
location / {
# First attempt to serve request as file, then
# as directory, then fall back to displaying a 404.
# try_files $uri $uri/ =404;
proxy_pass http://localhost:5000/;
proxy_http_version 1.1;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection "upgrade";
proxy_set_header Host $host;
}
This should prevent connection reverting to long-polling.
Reload nginx:
sudo nginx -s reload
The default under /etc/nginx/sites-available/ looks like this:
server {
listen 80 default_server;
listen [::]:80 default_server;
root /var/www/html;
# Add index.php to the list if you are using PHP
index index.html index.htm index.nginx-debian.html;
server_name _;
location / {
# First attempt to serve request as file, then
# as directory, then fall back to displaying a 404.
# try_files $uri $uri/ =404;
proxy_pass http://localhost:5000/;
proxy_http_version 1.1;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection "upgrade";
proxy_set_header Host $host;
}
Miscrosoft reference on how to deploy.

Answer 2

I just solved the problem. The server block was redirecting to SSL, but when I called the upstream I was not doing it with HTTPS!
To solve the problem I just changed
proxy_pass http://dotnet;
to
proxy_pass https://dotnet;
and now everything works.