HW3 - Queues, Caches and Proxies

Setup

Install redis
Start redis server by the command redis-server
Install dependencies by running npm install
Run sudo node main.js to start

Tasks

• set/get: On visiting /set, a key is set with a message. On visiting /get, the message is displayed. This message expires in 10 sec.
• recent: On visiting /recent, the 5 most recently visted urls will be displayed. They are stored in a redis queue, and are fetched from there. I have used ltrim, lrange and lpush to store them.
• upload: On visiting /upload, an image is uploaded by running the command
  curl -F "image=@./img/morning.jpg" localhost:3000/upload
  I have used lpush to store these images in a redis queue.
• meow: On visiting /meow, the most recent image will be displayed. I have used lpop to remove the image from the queue after it has been displayed.
• spawn: On visiting /spawn, a new app server is created. I have used a count for the port number on which the server will run. After a server is created, the count is incremented. I have used lpush to store the port numbers in the queue.
• destroy: On visiting /destroy, a random number between 1 and the number of new ports will be generated. This server will be destroyed, i.e, it will be removed from the queue. I have used lrem to remove it from the queue.
• listservers: On visiting listservers, the port numbers will be fetched from the redis queue and will be displayed on the webpage. I have used lrange for this purpose.
• proxy server: A proxy server is created on port number 80. I have used the http-proxy library for this purpose. I have used two servers on port numbers 3000 and 3001. These are stored in a redis queue. Everytime http://localhost is visited, it will redirect to http://localhost:3000 and http://localhost:3001 alternately. I have used rpoplpush to toggle between the two.

Screencast

Link