I'm using Nginx and magento 2 (php7) on Ubuntu when i try to open localhost in order to run setup I m getting HTTP ERROR 500 in browser and my nginx log file says:
 
[error] 6714#6714: *1 FastCGI sent in stderr: "PHP message: PHP Fatal error:  Uncaught Error: Cannot instantiate interface Magento\Framework\App\Config\Scope\ReaderPoolInterface in /var/www/nginx/bookstore/vendor/magento/framework/ObjectManager/Factory/Dynamic/Developer.php:73
Stack trace:
#0 /var/www/nginx/bookstore/vendor/magento/framework/ObjectManager/ObjectManager.php(71): Magento\Framework\ObjectManager\Factory\Dynamic\Developer->create('Magento\\Framewo...')
#1 /var/www/nginx/bookstore/vendor/magento/framework/ObjectManager/Factory/AbstractFactory.php(126): Magento\Framework\ObjectManager\ObjectManager->get('Magento\\Framewo...')
#2 /var/www/nginx/bookstore/vendor/magento/framework/ObjectManager/Factory/Dynamic/Developer.php(53): Magento\Framework\ObjectManager\Factory\AbstractFactory->resolveArgument(Array, 'Magento\\Framewo...', NULL, 'readerPool', 'Magento\\Framewo...')
#3 /var/www/nginx/bookstore/vendor/magento/framework/ObjectManager/Factory/Dynamic/Developer.php(82): Magento\Framework\ObjectManager\Factory\Dynamic\Developer->_resolveArgum" while reading response header from upstream, client: 127.0.0.1, server: localhost, request: "GET / HTTP/1.1", upstream: "fastcgi://127.0.0.1:9000", host: "localhost" 
 
This is my nginx default.conf: 
upstream fastcgi_backend {
   server   127.0.0.1:9000;
}
server {
   listen 80;
   server_name localhost;
   set $MAGE_ROOT /var/www/nginx/bookstore/;
   set $MAGE_MODE developer;
   include /var/www/nginx/bookstore/nginx.conf.sample;
} 
 
And nginx.conf.sample:
 
## Example configuration:
# upstream fastcgi_backend {
#    # use tcp connection
#    # server  127.0.0.1:9000;
#    # or socket
#    server   unix:/var/run/php5-fpm.sock;
# }
# server {
#    listen 80;
#    server_name mage.dev;
#    set $MAGE_ROOT /var/www/magento2;
#    include /vagrant/magento2/nginx.conf.sample;
# }
#
## Optional override of deployment mode. We recommend you use the
## command 'bin/magento deploy:mode:set' to switch modes instead.
##
## set $MAGE_MODE default; # or production or developer
##
## If you set MAGE_MODE in server config, you must pass the variable into the
## PHP entry point blocks, which are indicated below. You can pass
## it in using:
##
## fastcgi_param  MAGE_MODE $MAGE_MODE;
##
## In production mode, you should uncomment the 'expires' directive in the /static/ location block
root $MAGE_ROOT/pub;
index index.php;
autoindex off;
charset UTF-8;
error_page 404 403 = /errors/404.php;
#add_header "X-UA-Compatible" "IE=Edge";
# PHP entry point for setup application
location ~* ^/setup($|/) {
    root $MAGE_ROOT;
    location ~ ^/setup/index.php {
        fastcgi_pass   fastcgi_backend;
        fastcgi_index  index.php;
        fastcgi_param  SCRIPT_FILENAME  $document_root$fastcgi_script_name;
        include        fastcgi_params;
    }
    location ~ ^/setup/(?!pub/). {
        deny all;
    }
    location ~ ^/setup/pub/ {
        add_header X-Frame-Options "SAMEORIGIN";
    }
}
# PHP entry point for update application
location ~* ^/update($|/) {
    root $MAGE_ROOT;
    location ~ ^/update/index.php {
        fastcgi_split_path_info ^(/update/index.php)(/.+)$;
        fastcgi_pass   fastcgi_backend;
        fastcgi_index  index.php;
        fastcgi_param  SCRIPT_FILENAME  $document_root$fastcgi_script_name;
        fastcgi_param  PATH_INFO        $fastcgi_path_info;
        include        fastcgi_params;
    }
    # Deny everything but index.php
    location ~ ^/update/(?!pub/). {
        deny all;
    }
    location ~ ^/update/pub/ {
        add_header X-Frame-Options "SAMEORIGIN";
    }
}
location / {
    try_files $uri $uri/ /index.php?$args;
}
location /pub/ {
    location ~ ^/pub/media/(downloadable|customer|import|theme_customization/.*\.xml) {
        deny all;
    }
    alias $MAGE_ROOT/pub/;
    add_header X-Frame-Options "SAMEORIGIN";
}
location /static/ {
    # Uncomment the following line in production mode
    # expires max;
    # Remove signature of the static files that is used to overcome the browser cache
    location ~ ^/static/version {
        rewrite ^/static/(version\d*/)?(.*)$ /static/$2 last;
    }
    location ~* \.(ico|jpg|jpeg|png|gif|svg|js|css|swf|eot|ttf|otf|woff|woff2)$ {
        add_header Cache-Control "public";
        add_header X-Frame-Options "SAMEORIGIN";
        expires +1y;
        if (!-f $request_filename) {
            rewrite ^/static/(version\d*/)?(.*)$ /static.php?resource=$2 last;
        }
    }
    location ~* \.(zip|gz|gzip|bz2|csv|xml)$ {
        add_header Cache-Control "no-store";
        add_header X-Frame-Options "SAMEORIGIN";
        expires    off;
        if (!-f $request_filename) {
           rewrite ^/static/(version\d*/)?(.*)$ /static.php?resource=$2 last;
        }
    }
    if (!-f $request_filename) {
        rewrite ^/static/(version\d*/)?(.*)$ /static.php?resource=$2 last;
    }
    add_header X-Frame-Options "SAMEORIGIN";
}
location /media/ {
    try_files $uri $uri/ /get.php?$args;
    location ~ ^/media/theme_customization/.*\.xml {
        deny all;
    }
    location ~* \.(ico|jpg|jpeg|png|gif|svg|js|css|swf|eot|ttf|otf|woff|woff2)$ {
        add_header Cache-Control "public";
        add_header X-Frame-Options "SAMEORIGIN";
        expires +1y;
        try_files $uri $uri/ /get.php?$args;
    }
    location ~* \.(zip|gz|gzip|bz2|csv|xml)$ {
        add_header Cache-Control "no-store";
        add_header X-Frame-Options "SAMEORIGIN";
        expires    off;
        try_files $uri $uri/ /get.php?$args;
    }
    add_header X-Frame-Options "SAMEORIGIN";
}
location /media/customer/ {
    deny all;
}
location /media/downloadable/ {
    deny all;
}
location /media/import/ {
    deny all;
}
# PHP entry point for main application
location ~ (index|get|static|report|404|503)\.php$ {
    try_files $uri =404;
    fastcgi_pass   fastcgi_backend;
    fastcgi_buffers 1024 4k;
    fastcgi_param  PHP_FLAG  "session.auto_start=off \n suhosin.session.cryptua=off";
    fastcgi_param  PHP_VALUE "memory_limit=768M \n max_execution_time=600";
    fastcgi_read_timeout 600s;
    fastcgi_connect_timeout 600s;
    fastcgi_index  index.php;
    fastcgi_param  SCRIPT_FILENAME  $document_root$fastcgi_script_name;
    include        fastcgi_params;
}
gzip on;
gzip_disable "msie6";
gzip_comp_level 6;
gzip_min_length 1100;
gzip_buffers 16 8k;
gzip_proxied any;
gzip_types
    text/plain
    text/css
    text/js
    text/xml
    text/javascript
    application/javascript
    application/x-javascript
    application/json
    application/xml
    application/xml+rss
    image/svg+xml;
gzip_vary on;
# Banned locations (only reached if the earlier PHP entry point regexes don't match)
location ~* (\.php$|\.htaccess$|\.git) {
    deny all;
} 
 On localhost/setup page for localhost/setup/index.php/navigation(GET METHOD) and http://localhost/setup/index.php/session/prolong(POST) I'm getting 403 in network inspect element.