Use redis for session storage

Gemfile

 gem "sassc", "~> 2.2"
 
 gem "rake", "~> 13.0"
+
+gem "redis-rack", "~> 2.1"
+
+gem "rack", "~> 2.2"

Gemfile.lock

     rack-protection (2.0.8.1)
       rack
     rake (13.0.1)
+    redis (4.1.3)
+    redis-rack (2.1.2)
+      rack (>= 2.0.8, < 3)
+      redis-store (>= 1.2, < 2)
+    redis-store (1.8.2)
+      redis (>= 4, < 5)
     ruby2_keywords (0.0.2)
     sassc (2.2.1)
       ffi (~> 1.9)
   httparty (~> 0.18.0)
   nokogiri (~> 1.10)
   pg (~> 1.2)
+  rack (~> 2.2)
   rake (~> 13.0)
+  redis-rack (~> 2.1)
   sassc (~> 2.2)
   sequel (~> 5.30)
   sinatra (~> 2.0)

web/config.ru

+require 'rack'
+require 'rack/session/redis'
 require "rubygems"
 require "sinatra"
 
+use Rack::Session::Redis
+
 require '/var/www/vlv-search/web/server.rb'
 
 run VLVSearch