apache http server - Wordpress Permalinks not working in Nginx

I'm moving my wordpress blog from Apache to Nginx. I've tried multiple tutorials to get permalinks working but nothing is working for me. My website structure is like this:

main site -> www.localhost.com

wordpress blog -> www.localhost.com/blog

Website is in /var/www/html and wordpress is installed in /var/www/html/blog

I've read multiple articles and watched multiple videos but nothing seems to be working. Please let me know where I'm going wrong.

I've defined two server blocks in /etc/nginx/sites-available/default one for main site and one for the blog.

# Default server configuration
#
server {
    listen 80 default_server;
    listen [::]:80 default_server;

    # SSL configuration
    #
    # listen 443 ssl default_server;
    # listen [::]:443 ssl default_server;
    #
    # Note: You should disable gzip for SSL traffic.
    # See: https://bugs.debian.org/773332
    #
    # Read up on ssl_ciphers to ensure a secure configuration.
    # See: https://bugs.debian.org/765782
    #
    # Self signed certs generated by the ssl-cert package
    # Don't use them in a production server!
    #
    # include snippets/snakeoil.conf;

    root /var/www/html;

    # Add index.php to the list if you are using PHP
    index index.php index.html index.htm index.nginx-debian.html;

    server_name _;

       charset utf-8;
       error_page 404 /404.php;

       location /article {
         rewrite ^/article.* / redirect;
       }

       #location / {
        # try_files $uri $uri/ /loadpage.php?$args; 
       #}

       location ~ \.html$ {
         try_files $uri /courses/index.php?$args;
       }





    # pass the PHP scripts to FastCGI server listening on 127.0.0.1:9000
    #
    location ~ \.php$ {
        include snippets/fastcgi-php.conf;
    #
    #   # With php7.0-cgi alone:
    #   fastcgi_pass 127.0.0.1:9000;
        # With php7.0-fpm:
        fastcgi_pass unix:/var/run/php/php7.0-fpm.sock;
                include fastcgi_params;

    }

    # deny access to .htaccess files, if Apache's document root
    # concurs with nginx's one
    #
    location ~ /\.ht {
        deny all;
    }
}



server {
    listen 80;
    listen [::]:80;
    root /var/www/html/blog;
    index  index.php index.html index.htm;
    server_name  example.com www.example.com;

    location /blog/ {
    try_files $uri $uri/ /blog/index.php?$args;        
    }


    location ~ \.php$ {
    fastcgi_split_path_info  ^(.+\.php)(/.+)$;
    fastcgi_index            index.php;
 #  fastcgi_pass             unix:/var/run/php/php7.1-fpm.sock; #Ubuntu 17.10
    fastcgi_pass             unix:/var/run/php/php7.0-fpm.sock; #Ubuntu 17.04
    include                  fastcgi_params;
    fastcgi_param   PATH_INFO       $fastcgi_path_info;
    fastcgi_param   SCRIPT_FILENAME $document_root$fastcgi_script_name;
    }

}

Answer

By creating multiple server blocks for the same domain you are effectively creating a collision between the virtual servers. server blocks define what Nginx will listen for. If there are multiple virtual servers for a given port, the request will be passed on to a virtual server with the best matching server_name. By having multiple identical virtual servers, Nginx will have no way of telling where to pass it to.

Your main site and WordPress are under the same domain (and the same port) and thus should go in a single virtual server. You separate them using location blocks.

Take caution with the Nginx block selection algorithm, regular expression blocks are always evaluated before normal blocks. In your example everything ending with .html is send to your main site. This may interfere with WordPress when it tries to use URI's ending with .html as well. To prevent this, you can use nested location blocks. By moving the regular expression location block inside / it will only be evaluated when the parent location matches. When a request comes in for /blog, the /blog location block will be the best matching one and therefore will be selected over the / one. Because the regular expression block is now nested inside there, it won't be evaluated for requests to WordPress.

# Default server configuration
#
server {
    listen 80 default_server;
    listen [::]:80 default_server;

    # SSL configuration
    #
    # listen 443 ssl default_server;
    # listen [::]:443 ssl default_server;
    #
    # Note: You should disable gzip for SSL traffic.
    # See: https://bugs.debian.org/773332
    #
    # Read up on ssl_ciphers to ensure a secure configuration.
    # See: https://bugs.debian.org/765782
    #
    # Self signed certs generated by the ssl-cert package
    # Don't use them in a production server!
    #
    # include snippets/snakeoil.conf;

    root /var/www/html;

    # Add index.php to the list if you are using PHP
    index index.php index.html index.htm index.nginx-debian.html;

    server_name _;

    charset utf-8;
    error_page 404 /404.php;

    location /article {
        rewrite ^/article.* / redirect;
    }

    location / {
        location ~ \.html$ {
            try_files $uri /courses/index.php?$args;
        }

        try_files $uri $uri/ /loadpage.php?$args;
    }

    location /blog/ {
        try_files $uri $uri/ /blog/index.php?$args;
    }

    # pass the PHP scripts to FastCGI server listening on 127.0.0.1:9000
    #
    location ~ \.php$ {
        include snippets/fastcgi-php.conf;
    #
    #   # With php7.0-cgi alone:
    #   fastcgi_pass 127.0.0.1:9000;
        # With php7.0-fpm:
        fastcgi_pass unix:/var/run/php/php7.0-fpm.sock;
                include fastcgi_params;

    }

    # deny access to .htaccess files, if Apache's document root
    # concurs with nginx's one
    #
    location ~ /\.ht {
        deny all;
    }
}