Following NGINX server block can be used to run Drupal 7.

server {
        server_name YOURWEBSITENAME;
        root /var/www/html/drupal7;

        index index.php;

        location = /favicon.ico {
                log_not_found off;
                access_log off;
        }

        location = /robots.txt {
                allow all;
                log_not_found off;
                access_log off;
        }

There is sometimes a situation in which you have to theme each and every element displayed in a different way. There isn't any twig to override in case you need overriding till row level. To solve this problem can you can use for loop and iterate using row variable.

{% for row in rows %}

  {% if loop.index == 1 %}

    <!-- Do Some Changes -->

  {% endif %}

  {% if loop.index == 2 %}

    <!-- Do Some Changes --> 

  {% endif %}

{% endfor %}

You can install as explained in https://modulesunraveled.com/blog/install-drush-7-and-8-and-automatically-switch-versions-based-project.

After that go to settings.php and add the following line in $database array.

  'unix_socket' => '/Applications/MAMP/tmp/mysql/mysql.sock',
 

There might be a situation when you have to install a module programmatically in Drupal 8. You can achieve this with the help of Drush Invoke command. Make sure Drush is working fine on your system before using this function.

//This command will install and enable both devel and admin toolbar.

drush_invoke('pm-enable',['devel','admin_toolbar']);

Angular JS can be used for creating a headless Drupal website. To fetch a node data in angular you have to first expose nodes data by enabling REST related modules provided by Drupal 8 core. Once that has been done, you simply have to send an HTTP get a request from Angular to got JSON data of Drupal node.

Here is the angular JS code to achieve that 

$http.get("http://exampledrupalwebsite.com/node/1?_format=json") .then(function(response) { $scope.node_data = response.data; });

Most of the Drupal websites are getting converted to Headless applications. Most important configuration to achieve that is by enabling CORS in Drupal. If CORS is not enabled your headless app will not be able to fetch data from Drupal. To do that : 

1. Copy default.services.yml and create file services.yml.

2. Go to the last configuration in the file i.e CORS settings. Modify it in this way to allow cross-origin requests.

   # Configure Cross-Site HTTP requests (CORS).

   # Read https://developer.mozilla.org/en-US/docs/Web/HTTP/Access_control_CORS

In Drupal 8 by appropriate use of routing.yml and callback function/class, you can send values through URL. For eg, you a URL of type /data/{user-id}, on reaching this URL data should be loaded according to the user-id. This can be achieved in following way :

Here is the buildForm function for creating an AJAX form.

  public function buildForm(array $form, FormStateInterface $form_state) {
  
    $form = [];
    $form['email'] = [
      '#type' => 'textfield', 
      '#attributes' => ['placeholder'=>'Enter your Email ID'],
      '#description' => 'Submit your email address to recieve updates',
      '#size' => 100,
      '#maxlength' => 150,
      '#required' => TRUE,  
    ];

In Drupal 7 you use behaviors to handle the form submission. It can be achieved in following way.

There might be a situation when you have to print a block at a specific location on the webpage. In that case, you can load the block and set up a variable which will be printed in twig file. This can be achieved by following way:

Add the following code in right preprocess in the .theme file.