ESI (Edge Side Includes) Language And Systems

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ESI (Edge Side Includes) Language And Systems

• By Aparna Yeddula

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ESI Language Specification1.0

• ESI is an XML-based markup language and similar
  to HTML-like markup language used to isolate
  dynamic page elements such as stock quotes and
  rotating banners for compilation at the "edge"
• ESI is designed to leverage client tools like
  caches to improve end-user perceived performance.
  Advantage Reduce processing overhead on the
  origin server
• ESI allows for dynamic content assembly at the
  edge of the network
• ESI enables Web pages to be broken down into
  fragments of differing cacheability profiles .
• Each fragment is treated as separate entity.
• Cached templates and fragments may be shared
  among multiple users
• ETS ESI Test Server
• Sniptes ESI includes points to HTML files, but
  they are not full HTML web pages, they are just
  small HTML portions that fit within a web page

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ESI

• The Origin server is the existing web-server. The
  ETS server now sits in-between the origin server
  and the user.
• The ETS server processes requests from the user
  and determines what parts of the page need to be
  retrieved from the Origin server.
• This is determined based on caching requirements
  and TTL(Time To Live) settings for each ESI tag.
• ETS is configured with the IP address and port
  for the Origin test server, thus allowing it to
  transparently forward requests and retrieve
  content, without disruption to the Origin server
  or web browser functions.
• Although the previous diagram shows that ETS and
  the origin test server are running on separate
  machine, you can install ETS on the same machine
  as the origin test server.

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ESI Features

• ESI tags keep dynamic content fresh with much
  less stress on the web server.
• ESI invalidation protocol offers the methods used
  to invalidate (expire)data on the edge by the
  origin server.
• Architecture spec. details the use of HTTP
  intermediaries to control content.
• JESI tag library spec. is intended to be
  convenient JSP application-level interface to the
  ESI tags for web caching functionality. Its
  purpose is to help in the use of ESI tags within
  a JSP application.

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What is available on esi.org?

• The ESI Web Page http//www.esi.org/, contains
  the following information
• Overview An introduction to ESI including the
  technical advantages of ESI
• Endorsers Various companies that endorse ESI,
  such as Akamai, ATG, BEA, IBM, Macromedia,
  Oracle, Silver Stream, Vignette, and others.
• Specifications
• ESI Language SpecificationThis specification
  defines ESI 1.0, the Edge Side Includes language,
  which allows content assembly by HTTP surrogates,
  by providing an in-markup XML-based language.
• Edge Architecture SpecificationThis document
  defines the Edge Architecture, which extend the
  Web infrastructure through the use of HTTP
  surrogates - intermediaries that act on behalf of
  an origin server
• ESI Invalidation ProtocolThis specification
  defines the ESI Invalidation Protocol, to allow
  for tight coherence between origin serves and
  surrogates (also know as "Reverse Proxies").
• JESI Tag Library SpecificationThe Java ESI tag
  library is intended to be the convenient JSP
  application-level interface to the ESI tags for
  web caching functionality. Its purpose is to
  facilitate the use of ESI tags within a JSP
  application.
• News Various news links to articles relating
  to, and about, ESI. And also some examples

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How many ESI tags are defined?

• ltesiinclude srcURI altURI
  onerrorcontinue/gt
• Example
• ltesiinclude
• src"http//example.com/1.html"
  alt"http//bak.example.com/2.html"
  onerror"continue"/gt
• ltesiinclude src"http//example.com/search?query
  (QUERY_STRINGquery)"/gt
• include element specifies a fragment for
  assembly.
• it does not have a closing tag.
• include statement tells ESI processors to fetch
  the resource specified by the src attribute.
• If src not found, then fetch the alt
  alternative resource.
• onerror attribute will delete the include
  element silently.

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Cont..

• ltesiinline nameURIfetchableyesno gt
• fragment to be stored within an ESI processor
• lt/esiinlinegt
• The esi processor will parse response and extract
  all inline fragments and store them
  independently, under the URI specified.
• Some inline fragments are only delivered as
  part of an HTTP response for another object.

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Cont..

• ltesichoosegt
• ltesiwhen test"(HTTP_COOKIEgroup)'Advanced'"
  gt ltesiinclude src"http//www.example.com/advance
  d.html"/gt
• lt/esiwhengt
• ltesiwhen test"(HTTP_COOKIEgroup)'Basic
  User'"gt ltesiinclude src"http//www.example.com/b
  asic.html"/gt
• lt/esiwhengt
• ltesiotherwisegt
• ltesiinclude src"http//www.example.com/new_user.
  html"/gt
• lt/esiotherwisegt
• lt/esichoosegt
• choose must have at least one when and
  optionally contain exactly
• one otherwise

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Cont..

• Exception handling is provided by the try
  element
• must contain exactly one instance of both an
  attempt and an except
• Statements other than include and inline will
  not trigger this error.

• ltesitrygt
• ltesiattemptgt
• ltesicomment text"Include an ad"/gt
• ltesiinclude src"http//www.ex.com/ad1.html"/gt
• lt/esiattemptgt
• ltesiexceptgt
• ltesicomment text"some HTML instead"/gt
• lta hrefwww.akamai.comgtwww.example.comlt/agt
• lt/esiexceptgt
• lt/esitrygt

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Cont..

• ltesicomment text"..." /gt
• Example
• ltesicomment text"animation will have a 24 hr
  TTL." /gt
• The comment element allows developers to
  comment their ESI instructions.
• Comments are not evaluated by ESI Processors
  they are deleted before output. Comments that
  need to be visible in the output should use
  standard XML/HTML comment syntax.
• ltesiremovegt .. lt/esiremovegt
• Example
• ltesiinclude src"http//www.example.com/ad.html"/
  gt ltesiremovegt lta href"http//www.example.com"gtww
  w.example.comlt/agt lt/esiremovegt
• discarding the remove element and its contents

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Cont..

• ltesivarsgt ... lt/esivarsgt
• Example
• ltesivarsgt ltimg src"http//www.example.com/(HTTP
  _COOKIEtype)/hello.gif"/ gt
• lt/esivarsgt
• To include an ESI variable in markup outside an
  ESI block

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Cont ..

• lt!--esi ...--gt
• Example
• lt!--esi ltpgt ltesivarsgtHello,
  (HTTP_COOKIEname)!lt/esivarsgtlt/pgt --gt
• This is a special construct to allow HTML marked
  up with ESI to render without processing. ESI
  Processors will remove the start ("lt!--esi") and
  end ("--gt") when the page is processed, while
  still processing the contents. If the page is not
  processed, it will remain, becoming an HTML/XML
  comment tag
• This assures that the ESI markup will not
  interfere with the rendering of the final HTML if
  not processed.

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Simple Code

• ltesitrygt
• Invalid markup here
• ltesiattemptgt
• ltesiinclude ... gt
• This line is valid and will be processed.
• lt/esiattemptgt
• Invalid markup here
• ltesiexceptgt
• This HTML line is valid and will be processed.
  
• lt/esiexceptgt
• Invalid markup here
• lt/esitrygt

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Example

1. lthtmlgtltheadgtlttitlegt An example ESI
   templategtlt/titlegtltbodygt
2. ltesitrygt
3. ltesiattemptgt
4. ltesiinclude src"www. mysite.com/myad.html"
   onerror"continue" /gt
5. lt/esiattemptgt
6. ltesiexceptgt
7. Write some HTML for the ad instead
8. lt/esiexceptgt
9. lt/esitrygt
10. static content
11. lt/bodygtlt/htmlgt

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Look at these lines to examine how ESI works

• Line 2 This ESI tag specifies that the ESI
  processor should try to include some dynamic
  content. The only valid subtags, or children, of
  the try tag are attempt and except. Developers
  may notice that this closely resembles the
  try..catch..finally pattern of exception handling
  in languages such as Java and C.
• Lines 3, 4 and 5 These tags instruct the
  processor to attempt to fetch a fragment. Note
  that the tag is properly closed as per XML
  document rules. The onerror attribute of the
  include tag instructs the ESI processor to
  gracefully delete the error message that may be
  returned and to continue processing the page.
• Lines 6, 7 and 8 These tags indicate what action
  should occur if the fragment specified in the
  attempt tag cannot be loaded.
• Line 9 Again, the try tag is properly closed.
• Lines 10 and 11 Other content, including
  additional fragments or native markup, may be
  included.

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Lessons Learned Configuration Issues

• The ETS server acts as an intermediary between
  the client and the web server. My original
  thought was that the existing web server would
  reference out to the ETS server for the necessary
  ESI tags. Actually the opposite is true, the ETS
  server references out to the Origin web server.
• For configuration purposes this means that the
  HTML code needs to resided on the Origin(main)
  web server NOT on the ETS server
• Additionally the HTML snippets referenced by the
  ESI include tags need to reside on the Origin web
  server or any other server referenced by the ETS
  server.

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Setting up/testing the demo/servers

• The Windows Version of the ETS server was not
  working. So what we have done was, we took the
  Linux Version of the ETS server and the origin
  server remain same(Windows2000 advanced server).
• In the Linux Version
• - To extract the installation files from the tar
  file
• tar xzvf ETS_1.0Beta3_Linux.tar.gz
• - Start install ./install on installation make
  sure on port 80 there is no web server running.
  And set the origin server and its port number.
• My installation was not successful as it was
  running web server on port 80. So go to the
  directory ./usr/local/ETS/bin at the prompt enter
  ./ets_config. And make sure you also make changes
  in the ./etc/httpd/conf/httpd.conf file.
• To start the ETS server go to directory
  ./usr/local/ETS/bin and enter apachectl start
  and to stop enter apachectl stop

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ESI test pages

• http//gallop.uccs.edu/ayeddula/esi/testesi.html
•  
• http//gallop.uccs.edu/ayeddula/esi/home.html
• http//gallop.uccs.edu/ayeddula/esi/test.html

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References

• ESI resource web page http//developer.akamai.com/
  cfcgi/registration.cfm
• ESI Web Page http//www.esi.org/
• Edge Side Includes for Java http//www.akamai.com/
  jesi.html
• Emerging ESI Lower Costs, Better Performance
  http//www.networkcomputing.com/1301/1301ws12.html