Q:

nginx fails to load wordpress subfolder using different root location

We have a wordpress install in a subfolder of the root domain which is in a different path, even when using root in the location, the wordpress install still loads the root of the domains site.
server {
  listen              80;
  server_name         domain.com;
  return              301 https://$server_name$request_uri;
}

server {
  listen              443 ssl;
  server_name         domain.com;

  ssl                 on;
  #ssl_certificate     /var/www/certs/star.domain.com.cert;
  #ssl_certificate_key /var/www/certs/star.domain.com.key;
  ssl_certificate      /var/www/certs/cert_chain.crt;
  ssl_certificate_key  /var/www/certs/__domain_com.key;
  ssl_protocols       SSLv3 TLSv1 TLSv1.1 TLSv1.2;
  ssl_ciphers         ALL:!aNULL:!ADH:!eNULL:!LOW:!EXP:RC4+RSA:+HIGH:+MEDIUM;

  return              301 https://www.$server_name$request_uri;
}

server {
  ## Default Server Settings
  include             /etc/nginx/basic.conf;

  listen              443 ssl;
  server_name         www.domain.com;

  access_log          /var/log/nginx/domain.access.log;
  error_log           /var/log/nginx/domain.error.log;

  root                /var/www/domain/current;
  index               index.php index.html;

  ssl                 on;
  #ssl_certificate     /var/www/certs/star.domain.com.cert;
  #ssl_certificate_key /var/www/certs/star.domain.com.key;
  ssl_certificate      /var/www/certs/cert_chain.crt;
  ssl_certificate_key  /var/www/certs/__domain_com.key;
  ssl_protocols       SSLv3 TLSv1 TLSv1.1 TLSv1.2;
  ssl_ciphers         ALL:!aNULL:!ADH:!eNULL:!LOW:!EXP:RC4+RSA:+HIGH:+MEDIUM;

  error_page          404 /index.php;

  location / {
    try_files $uri $uri/ $uri.php?$query_string;
  }

location /blog {
    root /var/www/;
    try_files $uri $uri/ /blog/index.php?q=$request_uri;
}

location ~ /blog/.+\.php$ {
  try_files $uri $uri/ /blog/index.php?q=$request_uri =404;
  include       /etc/nginx/fastcgi_params.conf;
  fastcgi_pass  127.0.0.1:9000;
  fastcgi_index index.php;
}

}

This should work according to
https://www.nginx.com/resources/wiki/start/topics/tutorials/config_pitfalls/#root-inside-location-block
Here is the curl request to the root of the domain:
[root@callloop-web-1 www]# curl -IL callloop.com
HTTP/1.1 301 Moved Permanently
Server: nginx/1.6.3
Date: Fri, 21 Apr 2017 19:31:27 GMT
Content-Type: text/html
Content-Length: 184
Connection: keep-alive
Location: https://callloop.com/

HTTP/1.1 301 Moved Permanently
Server: nginx/1.6.3
Date: Fri, 21 Apr 2017 19:31:27 GMT
Content-Type: text/html
Content-Length: 184
Connection: keep-alive
Location: https://www.callloop.com/

HTTP/1.1 200 OK
Server: nginx/1.6.3
Date: Fri, 21 Apr 2017 19:31:28 GMT
Content-Type: text/html; charset=UTF-8
Connection: keep-alive
Vary: Accept-Encoding
Set-Cookie: PHPSESSID=3obiecqr3rm4i1q1bas8rcripdfuv8ru; path=/; HttpOnly
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Pragma: no-cache

And the access logs:
104.236.27.189 - - [21/Apr/2017:19:31:28 +0000] "HEAD / HTTP/1.1" 200 0 "-" "curl/7.29.0"

and now the subfolder:
[root@callloop-web-1 www]# curl -IL callloop.com/blog
HTTP/1.1 301 Moved Permanently
Server: nginx/1.6.3
Date: Fri, 21 Apr 2017 19:33:27 GMT
Content-Type: text/html
Content-Length: 184
Connection: keep-alive
Location: https://callloop.com/blog

HTTP/1.1 301 Moved Permanently
Server: nginx/1.6.3
Date: Fri, 21 Apr 2017 19:33:27 GMT
Content-Type: text/html
Content-Length: 184
Connection: keep-alive
Location: https://www.callloop.com/blog

HTTP/1.1 301 Moved Permanently
Server: nginx/1.6.3
Date: Fri, 21 Apr 2017 19:33:27 GMT
Content-Type: text/html
Content-Length: 184
Location: https://www.callloop.com/blog/
Connection: keep-alive

HTTP/1.1 404 Not Found
Server: nginx/1.6.3
Date: Fri, 21 Apr 2017 19:33:27 GMT
Content-Type: text/html; charset=UTF-8
Connection: keep-alive
Vary: Accept-Encoding
Set-Cookie: PHPSESSID=1lo0hrgkcrsrtstlldnr8gr3o2vu20if; path=/; HttpOnly
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Pragma: no-cache

access logs
104.236.27.189 - - [21/Apr/2017:19:33:27 +0000] "HEAD /blog HTTP/1.1" 301 0 "-" "curl/7.29.0"
104.236.27.189 - - [21/Apr/2017:19:33:27 +0000] "HEAD /blog/ HTTP/1.1" 404 0 "-" "curl/7.29.0"

So you can see a 404, makes sense but I have no idea WHY

A:

You are missing a root statement in your location ~ /blog/.+\.php$ block. But you may find it easier to read if you nest the location blocks:
location ^~ /blog {
    root /var/www/;
    try_files $uri $uri/ /blog/index.php?q=$request_uri;

    location ~ \.php$ {
        try_files $uri =404;
        include       /etc/nginx/fastcgi_params.conf;
        fastcgi_pass  127.0.0.1:9000;
    }
}

