Enable all three worker servers

README.md

-# Distributed Systems project: A URL shortener
+# Distributed Systems project: A simple URL shortener
 
 ## Table of contents
 
 - [Project structure](#project-structure)
 - [Overview](#overview)
 - [Deployment](#deployment)
+- [Getting started](#getting-started)
+    - [Introducing further workers](#introducing-further-workers)
 - [API](#api)
 
 ## Project structure
@@ -21,6 +23,7 @@
  │   │   └─ worker/files/
  │   │       └─ systemd/system/
  │   │           ├─ cockroach.service.d/override.conf
+ │   │           ├─ memcached.service.d/override.conf
  │   │           └─ shortener.service  # systemd service to start the URL shortener 
  │   ├─ frontend.yml
  │   └─ worker.yml
@@ -65,25 +68,41 @@ The project is currently deployed using an embedded Tomcat instance, the default
 by Spring Boot, which serves both static files and handles API requests.
 Requests are handled on one of the workers picked by HAProxy which is running on the frontend server.
 
-## Introducing further workers
+## Getting started
 
 Currently three worker servers are used with each one running one instance of our backend application,
-an Apache HTTP Server instance and a CockroachDB node.
+an embedded Tomcat instance, CockroachDB node, and a memcached server.
 
-At the present time some configuration files need to be edited in order to introduce further workers.
 The workers are automatically assigned an IP address of the form `192.168.10.(10 + N)` where `N` is
-the index of the worker starting with 1.
+the index of the worker starting with 1. Their names follow a similar scheme, namely `worker-N`.
+
 The IP address `192.168.10.10` is reserved for the frontend server responsible for running the load
-balancer and initializing the CockroachDB database cluster at provision time.
+balancer which redirects requests to one of the background workers.
+
+Simply running `vagrant up` should get you started. The process brings up the workers first followed
+by the frontend server, the latter of which initializes the CockroachDB cluster.
+Once all virtual machines have been started the frontend should be reachable under
+[192.168.10.10](http://192.168.10.10).
+
+### Introducing further workers
 
+At the present time some configuration files need to be edited in order to introduce further workers.
 The following files currently need to be changed when one wants to add or remove a worker:
 
-- The `num_workers` variable in `Vagrantfile`
-- The `haproxy.cfg` file located at `/ansible/roles/frontend/files/haproxy/haproxy.cfg`
-- `/ansible/roles/worker/files/systemd/system/cockroach.service.d/override.conf`
+- The `num_workers` variable in `Vagrantfile` in order to add more worker virtual machines
+
+- The `haproxy.cfg` file located at `/ansible/roles/frontend/files/haproxy/haproxy.cfg`, to make allow
+  the additional worker servers to be reachable from the frontend server's load balancer
+
+- `/ansible/roles/worker/files/systemd/system/cockroach.service.d/override.conf` to add the additional
+  CockroachDB instances on the new workers to the cluster
+
+- `/ansible/roles/worker/files/systemd/system/shortener.conf` to add the additional memcached instances
+  on the new workers to be reachable from all the clients
 
-Both of the latter two files should be changed at some point to make use of Ansible's templating
-feature so that only `num_workers` has to be edited, at least this should be possible.
+All of the files named above except for  the `Vagrantfile` should be changed at some point to make
+use of Ansible's templating feature so that only `num_workers` has to be edited, at least this
+should be possible.
 
 ## API
 

ansible/roles/frontend/files/haproxy/haproxy.cfg

@@ -4,5 +4,5 @@ frontend main
 
 backend workers
     server worker-1 192.168.10.11:8080 check
-#   server worker-2 192.168.10.12:8080 check
-#   server worker-3 192.168.10.13:8080 check
+    server worker-2 192.168.10.12:8080 check
+    server worker-3 192.168.10.13:8080 check

ansible/roles/worker/files/systemd/system/shortener.service

@@ -2,7 +2,7 @@
 Description=upbshrt.xyz backend
 
 [Service]
-Environment=MEMCACHED_CLIENTS="192.168.10.11:11211"
+Environment=MEMCACHED_CLIENTS="192.168.10.11:11211 192.168.10.12:11211 192.168.10.13:11211"
 ExecStart=/usr/bin/java -jar /opt/shortener/shortener.jar
 
 [Install]