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web performance Training Session Bernard Paques, March, 2007
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web performance Training Session
Bernard Paques, March, 2007
why do we have to learn on web performance?
Application? Network? Hosts?
• Bandwidth • Latency • Congestion
• Client • Server
• Processing Time • Sending Time
• Too many exchanges • Too much data • Serialized requests …
Response times of corporate distributed applications
The network team has to take the initiative
training on web performance
q Understanding HTTP, the web protocol § specifications and implementations
q Best practices in web performance management § assessment of web performance § recommendations to web designers and to webmasters
q Troubleshooting the web § practical steps and methodology § mastering the toolbox
q This training is for you if: § you have to interact with web designers or web masters, § you would like to refine ITM positioning, § you are curious about improving or troubleshooting web transactions.
HTTP, the web protocol
the world-wide web, by CERN (1994)
what the w3 has defined:
q the idea of a boundless world in which all items have a reference by which they can be retrieved,
q the address system (URL) implemented to make this world possible, despite many different protocols,
q a network protocol (HTTP) used by native web servers giving features not otherwise available,
q a markup language (HTML) which every web client is required to understand, and is used for the transmission of basic things,
q the body of data available on the Internet using all or some of the preceding listed items.
most related standards are freely available
q IETF § RFC2616 – HTTP 1.1 § RFC2617 – HTTP authentication § RFC2518 – WebDAV extensions § RFC2246 – TLS 1.0 § RFC2818 – HTTP over TLS § RFC2109 - cookies § RFC1952 – gzip § RFC2045, 2046, 2047 – MIME types § RFC4287 – ATOM 1.0
q W3C § XML
web server
HTTP is about clients talking to servers
IP network
web browser some HTTP request
server answer
HTTP transactions have many attributes
HTTP requests are chained, most often
Style sheets
HTML mixes data and their presentation
Document structure
<html> <head> </head> <body> <h1>Le titre de ma page</h1> <hr>
<table border="1" width="80%" align="center"> <tr> <td><img src="bouquetin.gif"></td> <td>Ceci est le contenu de cette cellule. </td> </tr> </table> <hr>
</body> </html>
Content and related resources
Extensible Markup Language, or XML for short, is a new technology for web applications.
XML is a World Wide Web Consortium standard that lets you create your own tags.
XML simplifies business-to-business transactions on the web
With XML, you can understand the meaning of the tags.
More importantly, a computer can understand them as well.
It's easier for a computer to understand that the tag <zipcode>34829</zipcode> is a zip code.
A DTD – Data Type Definition is used to identify the tags to be used in the XML message.
XML structures data
CAM S1BOOKED/QF2/81205/USD/1/BNO 3/ 341/EOIJ1234567/65B2468/1/EA/25.20/15073
<S1CPOXMTcmd> <CCD>S1BOOKED</CCD> <CIC>QF2</CIC> <SPL>81205</SPL> <ICR>USD</ICR> <POC>1</POC> <BNO>3</BNO> <S1CPOXMT_ORDER> <TNC>341</TNC> <CPO>EOIJ1234567</CPO> <PNR>65B2468</PNR> <QTO>1</QTO> <UNT>EA</UNT> <UNP>25.20</UNP> <SSD>20030715</SSD> </S1CPOXMT_ORDER>
</S1CPOXMTcmd> </S1CPOXMT>
Example: from SPEC2000 to XML
<?xml version="1.0" encoding="UTF-8"?> <!ELEMENT S1CPOXMT (SPEC_HDR?, S1CPOXMTcmd)> <!ELEMENT S1CPOXMTcmd (CCD, CIC, SPL, ICR, POC, BNO?, QTL?, EVT?, S1CPOXMT_ORDER+)> <!ELEMENT S1CPOXMT_ORDER (TNC, CPO, PNR, QTO, UNT, UNP, SSD, SSM?, SHT?, QTN?, SDC?, MFR?, PRI?, ACN?, DIS?, PKG?, LSE?, PBR?, PDP?, VRN?, ACK?, POU?, CTN?, REM*)> Include SPEC HDR Include Common Support Data Dictionary
<S1CPOXMTcmd> <CCD>S1BOOKED</CCD> <CIC>QF2</CIC> <SPL>81205</SPL> <ICR>USD</ICR> <POC>1</POC> <BNO>3</BNO> <S1CPOXMT_ORDER> <TNC>341</TNC> <CPO>EOIJ1234567</CPO> <PNR>65B2468</PNR> <QTO>1</QTO> <UNT>EA</UNT> <UNP>25.20</UNP> <SSD>20030715</SSD> </S1CPOXMT_ORDER>
</S1CPOXMTcmd> </S1CPOXMT>
DTD is used to identify XML tags
The writeable web is a very highly fragmented environment: business (micro-transactions), process (on-demand interactions), people (user-driven innovation), information (un-correlated data)
assessment of web performance
web server performance
IP infrastructure
Service Security Distance Last mile Rendering
· Service Time ¹ Transfer Time º User Time
End-to-end Response Time
data center user
(bare) performance model
Bytes / Throughput + Turns * Latency / Parallelism
Reduce turns (web designer) Reduce latency
Check size of TCP window
Response Time = Service Time + Transfer Time + User Time
Check available bandwidth Avoid drops
bandwidth vs. distance
130
Maximum speed = distance impact (latency)
Number of lanes = bandwidth impact (throughput)
also consider TCP built-in mechanisms
• The window size limits the bursts sent by the sender
• The window size is defined by the receiver (=size of buffer in memory)
• ‘Slow-start’ is a mechanism to ensure network condition may support burstiness
• The window is almost closed on any network problem
Server (sender) Client (receiver) Ti
me SYN
SYN ACK PACKET 1
ACK 1 PACKET 2 PACKET 3
ACK 3 PACKET 4 PACKET 5 PACKET 6 PACKET 7
ACK 7 • • •
FIN FIN ACK
TCP window
TCP window increases
what is a good performance level?
q Look at what others are doing: § benchmark against legacy competition (e.g., Boeing vs. Airbus), § also consider consumer sites (e.g., lastminute.com vs. airfrance.com)
q Manage user expectations § Where do they live? § From which network do they visit? § What connection speed do they enjoy? § What are the peak usage times and patterns of site visitation?
q Integrate technical constraints § Static or dynamic pages? § Web content, or multimedia? § Pure HTML, or Flash, or Java, or AJAX?
How Users View Application Task Performance
q Satisfied § User maintains concentration § Performance is not a factor in the user experience § Time limit threshold is unknowingly set by users and is consistent
q Tolerating § Concentration is impaired § Performance is now a factor in the user experience § User will notice how long it is taking
q Frustrated § Performance is typically called unacceptable § Casual user may abandon the process § Production user is very likely to stop working
how Apdex works
Tolerating
ApdexT= Total samples
Satisfied 2 +
Frustrated
Satisfied
Tolerating
Good
Fair
Poor
Una
ccep
tabl
e
0.00T
0.50T
1.00T
0.85T
0.94T
0.70T
Excellent Report Group: Application User Group Time Period
Existing Task Response Time Measurement
Samples
T 1
2
3
4 5
6 F
1. Define T for the application T = the application target time (threshold between satisfied and tolerating users). F = threshold between tolerating and frustrated users is calculated (F = 4T).
2. Define a Report Group (details available are tool dependent). 3. Extract data set from existing measurements for Report Group. 4. Count the number of samples in three performance zones. 5. Calculate the Apdex formula. 6. Display Apdex result (T is always shown as part of the result).
Apdex examples
On-line stock trading company Within the United States 0.793 Outside the United States 0.433
Retirement funds manager by their customers’ ISP
SBC (many dial-up users) 0.623 Sprint (mix of access types) 0.723 MCI (only corporate broadband access) 0.923
Supply chain management system
Original system across the United States 0.714 Adding content compression 0.904 Adding transparent turns reduction 0.944 Excel 4
Fair 3 Unax 3
Poor 3 Fair 3 Good 3
Fair 4 Good 4
recommendations in web performance
web deployment framework
Internet
Application
Origin Server Deployment Infrastructure
End-user
Production Interface
SSL/TLS sockets
HTTP requests
End-to-end latency
Bandwidth
Content overhead (fat index)
the web Fat Index
q It is a method to assess the noise / signal ratio, that is, a measurement of actual overhead
q Fat Index= 10 log( Total Bytes / Useful Bytes ) § Total Bytes = Sum for all network bytes exchanged during transaction § Useful Bytes = Displayed to end-user
q Typical values:
§ 1.2 db for a raw text file § 13 db to 17 db for popular dynamic Internet sites § 22 db for intranet web site
how to use the web Fat Index?
q A typical portal page: § 250 kbytes (inclusive all web objects) § 2 kbyte actually useful to end user § Fat Index = 10 log( 250 / 2 ) = 21 dB
q Caching may help a lot, except on first access q gzip compression may save up to 5 dB
q Shape a strategy, e.g.: § 10 dB on front page (first contact with brand) § 20 dB on authentication § 10 dB during navigation after login
where can data be cached?
Internet
Application
Origin Server
End-user
Reverse proxy cache
CDN (Akamai,
Netli)
Browser cache
Proxy cache
how to define a caching strategy
q The impact on usability is huge § End-user can admit delays on first access § Usually, expectations are higher for subsequent access § Navigating back has to be almost instantaneous
q How to not transmit same bytes again and again?
§ Browser validation § Server validation § Expiration scheme
q What cannot be cached?
§ Normally, web objects fetched through SSL/TLS § The outcome of POST requests
regular population of cache
Web Server
network Web Browser
GET /path/object
200 OK Last-Modified: <date> ETag: <unique string> Content-Length: <bytes>
Whole content is transmitted
browser (poor) validation
Web Server
network Web Browser
GET /path/object If-Modified-Since: … If-None-Match: … 200 OK
Socket Reset 1- Whole content is transmitted despite browser indications
2 - Browser tries to break the transfer
3 – The connection cannot be reused for other requests (HTTP 1.1)
Observed when server does not validate static content
server (normal) validation
Web Server
network Web Browser
GET /path/object If-Modified-Since: … If-None-Match: … 304 Use local copy
One RTT per request
cache dynamic objects (1/2)
Web Server
network Web Browser
GET /path/object
200 OK ETag: <unique string> Content-Length: <bytes>
Program steps: 1- compute page content 2- ETag = md5(content)
cache dynamic objects (2/2)
Web Server
network Web Browser
304 Use local copy
Program steps: 1- compute page content 2- ETag = md5(content) 3- if ETags are equals, sent 304 Use local copy 4- else sent content and code 200 OK
GET /path/object If-None-Match: …
No data is transmitted if client and server have same values for ETag
cache through expiration
Web Server
network
GET /path/object
200 OK Content-Length: <bytes> Expires: <deadline> Cache-Control: <max age>
Browser will use cached objects until time limits defined by server
Web Browser
how to define a compression strategy?
q The impact on usability is huge § Sensitivity to network conditions is reduced § Impact of TCP Receive Window Size (RWIN) is reduced
q How to avoid transmit overhead? § Compression is an effective way to approximate minimum message size
q Technology limitations § HTTP headers are not compressed § Compression may require more horse power on servers § Some browsers may badly process compressed content
how to compress dynamic objects?
Web Server
network Web Browser
GET /path/object Accept-Encoding:
200 OK Content-Encoding: gzip Content-Length: <bytes>
Program steps: 1- compute page content 2- if Accept-Encoding, compress content 3- sent content
Browser has to accept compression explicitly
Data is uncompressed on client side according to Content-Encoding
web packaging does impact end users
troubleshooting the web
start from the end-user
Security Web Server
Web Service
Database
1. Monitor the User Experience
2. Explain overall response time by subsequent analysis on connected components
overview of past assignments
Internet
Web servers
Origin Server
Airline
Proxy
1st hop
routing
LAN content
- Internet sub-optimal routing - polluting trafic (P2P) - poor DNS performance
- failure on the intranet - proxy delay - 1st hop congestion
DNS
P2P
the methodology for web troubleshooting
q Ensure end users have done their homework q Agree on reference transactions to be audited
§ Documented sequence of URLs, clicks, etc.
q Profile reference transactions § Play transactions in front of servers, and compute footprint figures.
q Capture data based on different scenarios § Play transactions in different situations and capture data. § Correlate these observations to estimate response time breakdown.
q Identify main sources of latency § This will be provided by a graphical “trace route” utility. § Also consider proxies and gateways
questions that end-user should answer
q Do browsers support HTTP/1.1 on workstation? q Do corporate proxies support HTTP/1.1 as well? q Less than 50 broadcast packet/s on the LAN? q Network delay and loss rate from workstation to the
proxy? (provided by ping) q Network delay and loss rate from intranet border to web
servers? (provided by ping) q Time requested to retrieve a public fixed web object
from servers? (found in proxy log) q Bandwidth utilisation of the Internet connection?
reference transactions
q To be discussed and provided by end-user
sample scenarios
q Client topologies: § Direct connection from behind the firewall § Direct connection in front of the firewall § Connection via Proxy-server § Connection via ADSL link (to benchmark the corporate Internet link) § Connection via SITA private infrastructure
q Service variations: § Direct connection to servers. § Connection to alternate servers (e.g., HTTP/1.1 instead of HTTP/1.0) § Connection to third party, for instance Akamai or equivalent.
start with internal tests
q Play reference transactions with your laptop, from within the intranet, through the proxy and directly
q In the background, record data § At the network level, with Application Vantage or Sniffer or … § At the application level, with TracePlus or Tamper Data or HTTPWatch, … § At the screen level, with SnagIt or Camcorder or …
q In case of security concerns, you may import Sniffer captures made by the Third Party into Application Vantage
Sample internal tests
intranet
SITA laptop
Internet
Proxy
TCP/80 & 443
Airbus
Singapore Airlines
Legacy AOLS
New Access Layer
SITA ATEX
Border tests
q First, launch PingPlotter to capture data related to network routes to servers.
q Play reference transactions with your laptop, from the demilitarized zone, or just in front of the ISP router
q In the background, record data § At the network level, with Application Vantage or Sniffer or … § At the application level, with TracePlus or Tamper Data or HTTPWatch, … § At the screen level, with SnagIt or Camcorder or …
Airbus
Sample border tests
Corporate PACNet
Singapore Airlines intranet Legacy
AOLS
New Access Layer
SITA laptop
Internet
Benchmark test (optional)
q First, launch PingPlotter to capture data related to network routes to servers.
q Play reference transactions with your laptop, from the demilitarized zone, or just in front of the ISP router
q In the background, record data § At the network level, with Application Vantage or Sniffer or … § At the application level, with TracePlus or Tamper Data or HTTPWatch, … § At the screen level, with SnagIt or Camcorder or …
Singapore Airlines premises
Airbus
Sample benchmark test
SITA laptop
Legacy AOLS
New Access Layer
Standalone Broadband Internet
Service variation (optional)
q Play reference transactions with your laptop against various hosts
q In the background, record data § At the network level, with Application Vantage or Sniffer or … § At the application level, with TracePlus or Tamper Data or HTTPWatch, … § At the screen level, with SnagIt or Camcorder or …
Sample tests related to web acceleration
intranet
SITA laptop
Internet
Airbus Singapore Airlines
New Access Layer
Akamai data center Proxy
useful tools
q Trace routes through the Internet § PingPlotter, from Nessoft
q Network Capture and Analysis § Application Vantage, from Compuware § Sniffer § Ethereal
q Web Capture and Analysis § TracePlus Web Detective, from SST § HTTPWatch § Tamper Data
q Screen capture § SnagIt, from TechSmiths Corporation § Camcorder
PingPlotter
q Use it during border or benchmark tests, to capture data related to end-to-end network path.
q Check every increase of round-trip-time. Is it expected (an ocean to cross) or suspect (a congestion)?
q High-level of latency on first hop proves undersizing of the Internet link to the ISP.
q If you suspect a congestion, capture data early in the morning, during business hours and late at night.
q If the tool reports on changing routes, augment duration of capture to prove flapping.
q Drops of ICMP packets are rarely correlated to application poor performance, except above 30% loss.
CPA to Europe, through PCCW
China
USA
France
260 ms due to the Pacific Ocean
and USA size
100 ms due to the
Atlantic Ocean
Regular link to Toulouse
U.A.E.
USA
Europe
expected
175 ms + loss
Air China Infrastructure Assessment Packet loss: Path from Beijing to Europe I
Average Round
Trip Time To
Airbus = 354 ms
No Packet
Loss
Air China Infrastructure Assessment Packet loss: Path from Beijing to Europe II
Average Round
Trip Time To
Airbus = 465 ms
AlmostNo
Packet Loss
Round Trip Time has increased with 100 ms
from day 1 to day 3
Alternatives to PingPlotter
q Some airlines may not let you plug your PC into their network
q Ask for MRTG diagrams instead
Application Vantage
q Capture network packets (= Sniffer) q Allows for graphical handling of them (# Sniffer)
§ Clean the capture (remove packets afterwards) § Compute footprints
q Shows network errors and retransmissions § Configure the software to change some errors to warnings
q Allows for a number of complementary tests § Number of sockets open § Time to open a socket (SYN-ACK) compared to RTT § Size of TCP receive window
TracePlus or HTTPWatch
q Capture web transactions, as seen at browser level q Useful to assess proxy efficiency
§ Compare time to first byte through the proxy with time to first byte on direct access
q Look at response header to check: § Cacheability of web objects § Compression § Web errors (404, 500, …)
Explain proxy impact
corporate ADSL Proxy
Airbus Emirates
Server
33 seconds
49 seconds
Indirect proof of proxy impact
corporate Internet Proxy/NTLM
Airbus Cathay Pacific
Server
Pilot Response Time Network Delay
9:00 9:15 9:30
323 ms 25 s
50 s
9:00 9:15 9:30
SnagIt
q A straightforward capture tool q Make it visual to help motivate decisions
§ 90 seconds, does it mean something to you? § Provide a 90 seconds video, this will make a big difference § Example: transaction using free ADSL link compared to transaction through
corporate saturated link § Put several videos on same slide, and trigger all of them at the same time
Knowledge test: how would you prove:
Internet
web servers
Origin Server
users
Proxy
1st hop
routing
LAN content
- Internet sub-optimal routing - polluting trafic (P2P) - poor DNS performance
- failure on the intranet - proxy delay - 1st hop congestion
DNS
P2P
lessons learnt
golden rules for web robustness Web definition Where is the competition? Set objectives for end-user response times Ask for XHTML/CSS Set data URLs for next 10 years
Web deployment HTTP/1.1 Compress dynamic web pages Validate dynamic web pages Expire static objects
Web development < 20 objects/page < 100 kbytes/HTML 20 dB Fat Index on 1st access, 10 dB afterwards Minimum Javascript No Java applet
Fat Index= 10 log( Total Bytes / Useful Bytes )
takeaways
q Understanding HTTP, the web protocol § do your homework, and read specifications
q Best practices in web performance management § ask the network team to sponsor you to enter web teams
q Troubleshooting the web § if it is not in the IETF specification, it will happen… § use your brain and ask your peers
Thank you [email protected]
