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| − | = Overview =
| + | [http://wiki.littlesvr.ca/wiki/OPS345_Assignment_1 This page has moved.] |
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| − | In this assignment you'll use many of the skills you learned so far to set up several Apache web servers with a lame load balancer. It won't be even close to production-ready but you will get more practice with the basics, which is what you need most now.
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| − | This assignment assumes that your www.youruserid.ops345.ca is a working web server. If you didn't complete that part of Lab 3: you'll need to do it first.
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| − | The format of the assignment is similar to a lab, but it's less specific about the exact steps you need to take. You're expected to show more independent learning abilities for an assignment than for a lab. The extra complicated parts are clarified for you here.
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| − | In short, a complete assignment will show that you can:
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| − | * Create AMIs from an existing VM and deploy new VMs based on that AMI.
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| − | * Use SSH keys, rsync, and cron to keep data on multiple servers synchronized.
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| − | * Use iptables as an Apache load balancer by directing traffic to a random slave.
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| − | This is the overview of your completed work in the form of a diagram:
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| − | [[File:AWSAsg1Overview.png|800px|border|center]] | |
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| − | = Part 1: first slave =
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| − | * Go to your www VM in the AWS Console and find the button to create an image from it.
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| − | ** Name the image www-for-asg1-p1
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| − | ** This will create an AMI with all the software configured the way you configured it.
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| − | * Deploy one new VM from the AMI you created above.
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| − | ** Name it www-slave1
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| − | ** With primary IP address 10.3.45.21
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| − | ** In ops345wwsg
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| − | ** Make sure the second virtual drive is named www-data-slave1
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| − | * Add the appropriate iptables rule on router (don't forget to save the iptables rules) and ops345routersg rule to allow yourself to SSH to www-data-slave1 via port 2221.
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| − | * Don't change the hostname of www-data-slave1, leave it as "www".
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| − | == Sync files with www ==
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| − | Each of your web servers (www and all the slaves) need to have the same data on them. That means you need to synchronize the contents of /var/www/html. You might recall this is mounted from a separate drive (/dev/xvdf) but that doesn't matter for this assignment.
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| − | You'll use rsync to do the synchronization, but first you need to set up your user on www-slave1 to be able to ssh to www without a password.
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| − | * Create an ssh key on www-slave1 as your regular user. Make sure the key is stored in /home/yourusername/.ssh/id_rsa_wwwsync
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| − | ** On www edit /home/yourusername/.ssh/authorized_keys
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| − | ** Paste the contents of /home/yourusername/.ssh/id_rsa_wwwsync.pub from www-slave1 to the end of that file as one line.
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| − | * Test your key authentication setup as yourusername on www-slave1 to confirm you can log in to yourusername@10.3.45.11 (www) without a password:<source>ssh -i /home/yourusername/.ssh/id_rsa_wwwsync yourusername@10.3.45.11</source>
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| − | Now set up rsync:
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| − | * Create a new file in /var/www/html on www and use this command on www-slave1 to make sure that new file is copied to www-slave1:<source>rsync -e "ssh -i ~/.ssh/id_rsa_wwwsync" -au --exclude="nextcloud" yourusername@10.3.45.11:/var/www/html/* /var/www/html</source>
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| − | * Create a new file in /var/www/html on www-slave1 and use this command on www-slave1 to make sure that new file is copied to www:<source>rsync -e "ssh -i ~/.ssh/id_rsa_wwwsync" -au --exclude="nextcloud" /var/www/html/* asmith15@10.3.45.11:/var/www/html</source>
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| − | * Once you confirm both rsync commands above work: make them run automatically every 5 minutes by editing your user's crontab on www-slave1:<source>*/5 * * * * rsync -e "ssh -i ~/.ssh/id_rsa_wwwsync" -au --exclude="nextcloud" asmith15@10.3.45.11:/var/www/html/* /var/www/html
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| − | */5 * * * * rsync -e "ssh -i ~/.ssh/id_rsa_wwwsync" -au --exclude="nextcloud" /var/www/html/* asmith15@10.3.45.11:/var/www/html</source>
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| − | * Test that by creating some files on www, some other files on www-slave1, and waiting more than 5 minutes.
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| − | = Part 2: iptables load balancing =
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| − | You already have HTTP (port 80) traffic forwarded from router to www. That means you've already done most of the work to set up iptables to do the load balancing.
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| − | * Confirm that you will see your website by going to your router's public IP with a web browser. If it doesn't work: go back to lab 3 and figure out why.
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| − | * When you're sure it works: save a backup copy of your iptables rules just in case: <source>cp /etc/sysconfig/iptables /root/iptables-before-asg1</source>
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| − | You can restore the working set of rules if you make a big mess, but try not to: you may lock yourself out of router altogether, and then you won't be able to restore the original rules either.
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| − | * Remove the existing port 80 rule from your nat table. Find the rule number with:<source>iptables -L -n -t nat</source>
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| − | * Add two new rules to send 50% of the incoming requests for port 80 to www, and the rest to www-slave-1:<source>
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| − | iptables -t nat -A PREROUTING -p tcp -m tcp --dport 80 -m statistic --mode random --probability 0.5 -j DNAT --to-destination 10.3.45.11:80
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| − | iptables -t nat -A PREROUTING -p tcp -m tcp --dport 80 -j DNAT --to-destination 10.3.45.21:80</source>
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| − | The two rules above are based on [https://scalingo.com/blog/iptables Yann Klis's blog post]. You should read that so you understand how they work.
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| − | * Test that your load balancer works by looking at the logs on both web servers and reloading your webpage in Firefox. After about 8 requests from Firefox the new requests will be directed to the other servers:<source>tail -f /var/log/httpd/access_log</source>
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| − | * You can also see the private IP address on your web page change: that's the actual IP address of the server processing the request, not the IP address of the load balancer.
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| − | = Part 3: two more slaves =
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| − | Once you're happy with all your work above: you are ready to create two more slaves and distribute the web server load across all four of your web servers.
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| − | * Create another AMI, this time from www-slave1 instead of www. Name it www-for-asg1-p3
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| − | * Deploy www-slave2 with ip address 10.3.45.22 and www-slave3 with ip address 10.3.45.23 from your new image.
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| − | * Do the work you need to allow SSH access to those two VMs. You won't need to change anything on them, they will be identical to www-slave1, but SSH access will help you make sure your work is done properly.
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| − | * Modify the iptables rules on your load balancer to make sure the load is distributed equally among all four web servers.
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| − | = Part 4: load test =
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| − | Refreshing your webpage in Firefox over and over again is not the best way to test your load balancer. You'll set up a Python script to do it instead. I wrote most of it for you:<source lang="python">#!/usr/bin/env python3
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| − | # asg1Test.py
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| − | # Test for OPS345 Assignment 1
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| − | # Author: Andrew Smith
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| − | # Student changes by: Your Name Here
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| − | import os
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| − | import re
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| − | numRunsLeft = 10
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| − | numMain = 0
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| − | numSlave1 = 0
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| − | while numRunsLeft > 0:
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| − | output = os.popen("curl --no-progress-meter http://3.210.171.214/")
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| − | curlOutput = output.read()
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| − | ip = re.search('10\.3\.45\...', curlOutput)
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| − | if ip[0] == '10.3.45.11':
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| − | numMain = numMain + 1
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| − | elif ip[0] == '10.3.45.21':
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| − | numSlave1 = numSlave1 + 1
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| − | numRunsLeft = numRunsLeft - 1
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| − | print('Hits on main www server: ' + str(numMain))
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| − | print('Hits on www-slave1 server: ' + str(numSlave1))</source>
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| − | All that's left for you to do is:
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| − | * Put your name in the comments at the top.
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| − | * Fix the part that's supposed to connect to your server instead of mine.
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| − | * Add to the script so that it counts slave2 and slave3 as well, and prints the results at the end.
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| − | * Once you're happy with the above: make it run for 60 seconds instead of 10 and record the results. The number of requests should be split almost perfectly between your for web servers.
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| − | = Submission =
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| − | = Why this assignment is stupid =
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| − | You're likely not ready for real load balancing on AWS, this assignment is the most I figured is reasonable to ask an average to do. So this assignment has some significant problems:
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| − | # Your website will be down for 25% of the requests for each server that's offline, since your load balancer doesn't know whether the slaves are alive or not.
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| − | # The storage is only synced in the worst case every 5 minutes (10 if the change is on a slave), that's unacceptably slow for current web applications.
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| − | # The two-way rsync syncing you set up won't syncronize deleting files.
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| − | # This sort of load balancing won't work with Nextcloud or most other non-trivial web applications that use cookies.
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| − | We might fix some of these problems later in OPS345.
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