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Lab Assignment #2 Solution
In this assignment, you will learn to develop and loadbalance your own infrastructure (a server farm) while applying your knowledge of DNS and other application entities and protocols.
You will also learn to use Cloud Storage for backup and recovery of your data. In addition, you will perform rudimentary analysis of the IP traffic.
You will use Nginx (a popular http server available at http://nginx.org/) to host a simple website on four Amazon EC2 instances; you will also configure an
Nginx server on another instance, which will act as a load balancer. You will learn how to distribute networking workload across multiple servers.
A total of 100 points will be assigned if you successfully implement the outlined steps. In addition, at the discretion of TA, you can be given extra points (up to the maximum of 50) for devising and programming your own mechanisms (including a creative web site) at various stages of the assignment. Use your ingenuity!
As before, remember to double check the Amazon SLAs and ensure that you take all the necessary steps not to exceed the resource use that
Amazon provides for free.
Please take the following steps:
Create the Amazon EC2 instances
You need to create five EC2 instances of the same time you have created in the previous homework. One of these instances will act as a load balancer; the other four will act as web servers named Server1, Server2, Server3, Server4, as demonstrated below:
Incoming traffic
|
Load Balancer
|
|
Server1 Server2 Server3 Server4
Install Nginx on each instance
After launching the instances, use yum (the Amazon Linux native software manager) to install Nginx on every instance and start the Nginx service.
To verify the Nginx is working, visit the hosted default webpage through instance's public DNS from an internet browser. You will see the Welcome message
(if Nginx http server works properly).
You need to edit the default index.html file on four servers. This file can be found in the directory /usr/share/nginx/html. Use
a text editor (such as vi) to replace the text in the index.html file with the following:
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en"
<body
<h1[SERVER_ID]</h1
</body
</html
Of course, you need to change SERVER_ID to the particular server name (i.e., Server1, Server2, Server3, or Server4).
Configure the load balancer
To configure the load balancer, you need to edit the load balancer’s configuration file /etc/nginx/nginx.conf.
Use a text editor (such as vi) to replace the existing text with the following:
events {
worker_connections 768;
}
http {
upstream myapp {
#ip_hash;
server [SERVER_PUBLIC_DNS_NAME] weight=1; server [SERVER_PUBLIC_DNS_NAME] weight=1; server [SERVER_PUBLIC_DNS_NAME] weight=1; server [SERVER_PUBLIC_DNS_NAME] weight=1;
}
server {
listen 80;
server_name myapp.com;
location / {
proxy_pass http://myapp;
}
}
}
Again, you need to find the public DNS name of your servers and replace each occurrence of the SERVER_PUBLIC_DNS_NAME with the respective string.
The assignment server[<name] weight=<number establishes the weight of the server in the upstream cluster to be equal to the specified <number. The present default is 1. To experiment with assigning some servers a greater proportion of the traffic, set weights correspondingly.
Then run the following command in the shell (this will cause the new configuration to take effect):
$ /etc/init.d/nginx reload
You also need to replace the SERVER_PUBLIC_DNS part with the public DNS of your instances.
Now you can use the curl command in the shell to visit the balancer, which will distribute traffic among the servers.
$ curl [LOAD_BALANCER_DNS_NAME]
1 Collect the information on visits to your site
You can use the visit server tool, provided in the Appendix, or write your own tool, to track the distribution of the load. The tool visits the cluster 2000 times and returns the visit count on each server.
The following example illustrates the use of this tool:
$ visit_server d LOAD_BALANCER_DNS_NAME The output would look like this:
Starting to visit load balancing server
Summary
Server1 visit counts : 500
Server2 visit counts : 500
Server3 visit counts : 500
Server4 visit counts : 500
Total visit counts : 2000
The following table shows three different scenarios of weight combination of the four servers. Configure the nginx.conf file according to these scenarios. Then use visit_server for each scenario, and record the outputs.
Scenario
Weight
Server 1
Server 2
Server 3
Server 4
Server
1
1
1
1
1
2
1
2
3
4
3
1
2
1
2
Submission
Your submission should include a report that includes
1) the description of the steps that you have done in this assignment;
2) the results of the execution of the three scenarios; and
3) all additional observations.
Appendix: The Visit Server program
#!/usr/bin/env ruby
#
This program is used for collecting web server visit information.
#
# Author: A. Genius
#
require 'optparse'
def print_usage
puts "USAGE: visit_server d DNS_NAME" exit
end
# add option switch and handler
options = {}
option_parser = OptionParser.new do |opts|
# DNS_NAME argument options[:dns_name] = nil
opts.on('d', 'dnsname DNS_NAME', 'Specify a DNS NAME') { |dns_name| options[:dns_name] = dns_name }
# HELP argument options[:help] = nil
opts.on('h', 'help', 'Display usage') { |help| options[:help] = help }
end
option_parser.parse!
# verify arguments
if options[:dns_name] then dns_name = options[:dns_name]
else
puts "Please set a balancer's DNS." print_usage
exit end
if options[:help] then print_usage
exit end
# Keep STDOUT
#orig_stdout = $stdout
# redirect stdout to /dev/null
#$stdout = File.new('/dev/null', 'w')
server1_visit_count = 0 server2_visit_count = 0 server3_visit_count = 0 server4_visit_count = 0
# starting to visit load balancing server
puts "Starting to visit load balancing server"
2000.times do
# visit load balancer
#o = `curl #{dns_name}`
o = `curl s #{dns_name}`
if o =~ /server\s*1/i server1_visit_count += 1
elsif o =~ /server\s*2/i server2_visit_count += 1
elsif o =~ /server\s*3/i server3_visit_count += 1
elsif o =~ /server\s*4/i server4_visit_count += 1
end
print "." end
# redirect output to stdout
#$stdout = orig_stdout
# print visit information puts
puts '' puts ' Summary'
puts ''
puts "Server1 visit counts : " + server1_visit_count.to_s puts "Server2 visit counts : " + server2_visit_count.to_s puts "Server3 visit counts : " + server3_visit_count.to_s puts "Server4 visit counts : " + server4_visit_count.to_s
puts "Total visit counts : " + (server1_visit_count + server2_visit_count + server3_visit_count + server4_visit_count).to_s
Additional steps are outlined below. Create EC2 by using command line
1. Use the `script` command to record all the commands you use to create the instance
2. Explain every step you have used to achieve your goal
After having deployed the balancer
1. Use the `tcpdump` command to collect all the packets that had been exchanged.
2. Analyze the packets and report your observations.
As an additional step, perform the EC2 backup and restore:
1. Create a new EC2 instance and backup it to a data storage device in the cloud.
2. [ *`ec2backup` backs up a directory into Elastic Block Storage (EBS)
3. Unmount he volume and remount it to a newlycreated EC2 instance
4. Verify that the restore was successful. List and explain all the steps in achieving this goal.
