Drupal 8 modules and Solarium installation

These steps are only for Drupal 8.

Download modules using Composer

Better download the modules using Composer than Drush. This will install the required libraries, including the class Solarium. General (deeper) instructions may be found at Using Composer to install Drupal packages through Drupal.org

Run these commands in the Drupal root folder.

First add the Drupal 8 Composer repository (only for Drupal 8.2.x and earlier):
composer config repositories.drupal composer https://packages.drupal.org/8

Download the module Search API Solr Search.
composer require drupal/search_api_solr

As at May 2019, if you are installing the Acquia Search module please make sure you that you install only the 1.2 release. Acquia Search is not currently compatible with 2 or greater.
composer require drupal/search_api_solr 1.2

If required, the line above automatically resolves all dependencies for you.

Enable modules and clear caches

drush en -y search_api_solr
drush cache-rebuild