Web Hosting
Michael Tsai 2018/05/28
Web Hosting Basics
•
A daemon (server) listens for connection on TCP port 80
•
Accept request for documents
•
Transmits them to the requesting user’s browser
Different Layers in Web
• Web page (HTML/XML) - frontend engineer
• Interface for interaction with users
• Program / script (PHP/ASP/etc.) - backend engineer
• Generation of web pages, logics, database query
• Database (Mysql, PgSQL, etc.) - database admin
• Data storage
• Web server (apache/nginx) - sys admin
• Operating System - sys admin
Our role
URL
•
URI = {URL, URN}
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URI: Unified Resource Identifier URL: Unified Resource Locator URN: Unified Resource Name (e.g., urn:isbn:0-13-020601-6)
•
URL: {protocol/app., hostname, [port, directory,
filename]}
URL Examples
Proto What it does Example
file accesses a local file file:///etc/syslog.conf ftp accesses a remote file
via FTP
ftp://ftp.admin.com/
adduser.tar.gz http accesses a remote file
via HTTP http://admin.com/index.html https accesses a remote file
via HTTP/SSL https://admin.com/order.shtml
ldap accesses LDAP
directory services
ldap://ldap.bigfoot.com:389/
cn=Herb mailto sends email to a
designated address mailto:linux@book.admin.com
How HTTP works
•
Stateless client/server protocol
•
A client
asks the server for the contents of a specific URL
•
The server responds with the data (or err. msg.)
•
Try it: telnet to port 80
Browser
• telnet to www.csie.ntu.edu.tw port 80 (http default TCP port)
• Type the following:
GET / HTTP/1.1
Host: www.csie.ntu.edu.tw (hit <enter> twice)
• What do you get?
• Try a nonexistent URL. What do you get?
Content Generation
• Dynamic content is better
1. CGI (Common Gateway Interface):
Allow external program to interact with the web server
2. FastCGI: Allow external program to continue running to server multiple requests
3. Embedded interpreters:
(e.g., Perl, PHP, Python, Ruby on Rails)
Executing external script within the server (.php, .pl)
e.g., LAMP: linux + apache + mysql + php/perl/python 4. Application servers:
Entire, full-fledge, platform for web
(e.g., Tomcat, WebSphere, WebLogic, Jetty)
Market Share:
Server-Side Programming Language
2017 2018
Security!
• Bottom line:
you allow the entire world to execute a script on your server (access to files, networks, and more!)
• Need to make sure that the script is secure
(as much as other network-accessible program)
• Read:
OWASP Top 10 Application Security Risks 2017 https://www.owasp.org/index.php/Top_10_2017- Top_10
SSL
• SSL = Secure Sockets Layer
• http -> https, SSL runs as a layer below HTTP
• Prevent eavesdropping, tampering, and message forgery
More on security-related topics in the 6/11 guest lecture
Load Balancing
• Many factors affecting the maximum load a server can handle:
• Hardware architecture
• Operating system
• System tuning
• Sites being served
(static vs dynamic (database))
• And, in addition, network bandwidth
• Stress testing - CPU, I/O, or network-bound? (usually not network)
Create Scalability
1. Round robin DNS (we’ve talked about it) Note that the order in the DNS record is irrelevant.
(Think about its disadvantage)
2. Hardware solution (e.g., Big-IP from F5)
Takes response time of individual servers into account
3. Software solution (e.g., Linux Virtual Server, proxy load balancing in Apache)
Scaling Beyond Limits
• Cloud computing (e.g., Amazon Web Services)
• Co-location hosting (like us, or some NTU services)
• Content Distribution Networks (e.g., akamai, limelight, edgecast)
• Putting static content close to users
• Try: https://www.cdnplanet.com/tools/cdnfinder/
• Pick a content-rich website (such as a news website) and see if it uses CDN
source: https://news.netcraft.com/archives/2017/03/24/
march-2017-web-server-survey.html
Apache
• Web server with the largest market share (53.8% of top M busiest sites, 2014/04)
• Runner-ups:
Microsoft & nginx take 17.8% and 12.4%
• Began in 1995
• First web server software to serve more than 100M sites (in 2009)
• Versatile
Nginx
• (pronounced “engine x”)
• Created in 2004
• Used by 57.0% of the top 10,000 websites.
(W3Techs)
• Written with an explicit goal to outperform Apache (less memory, 4x more requests per second)
• Less flexibility
Different Layers in Web
• Web page (HTML/XML) - frontend engineer
• Interface for interaction with users
• Program / script (PHP/ASP/etc.) - backend engineer
• Generation of web pages, logics, database query
• Database (Mysql, PgSQL, etc.) - database admin
• Data storage
• Web server (apache/nginx) - sys admin
• Operating System - sys admin
