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Understanding and Creating Aliases. October 27, 2010. Agenda. Aliases Redirects Resources. Aliases vs. Redirects. Alias False name to conceal one’s identity; Assumed name Used to make a web page or directory on the same server available under many URLs Redirect

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  • Aliases
  • Redirects
  • Resources
aliases vs redirects
Aliases vs. Redirects
  • Alias
    • False name to conceal one’s identity; Assumed name
    • Used to make a web page or directory on the same server available under many URLs
  • Redirect
    • To change the direction or course of
    • Used to make a web page or directory on the same or different server available under many URLs
  • Common uses:
    • Create user-friendly URLs
    • Change URL for content
  • Types used at EPA:
    • Symbolic Links
    • DNS Aliases
symbolic links
Symbolic Links
  • A text string that is interpreted by the operating system as a path to another file or directory
  • Used on the static web Linux servers: www.epa.gov, intranet.epa.gov, staging.epa.gov
  • Also used on other Linux servers (e.g., OAS)
  • All TSSMS accounts are a symbolic link
    • Data resides at /public/data/TSSMS/web
    • Symlink resolves to /TSSMS/ so that the URL www.epa.gov/TSSMS/ will render the content
symbolic links1
Symbolic Links
  • Since TSSMS accounts are 8-characters, need an alias to obtain a user-friendly URL
  • NCC Sys Admins place the symbolic link in the htdocs file
  • Example:
    • Content resides at www.epa.gov/opp00001/bedbugs/
    • Request symbolic link (alias) to obtain URL: www.epa.gov/bedbugs/
requesting an alias

Visit www.epa.gov/webguide

  • Select “Create or Remove Alias” under “Create a Web Area”
  • http://intranet.epa.gov/webmast3/webguide/aliasform.html
Requesting an Alias
fulfilling the request
Fulfilling the Request
  • Request goes to technical contracting team, OEAEE (formerly known and OPA) and OEI
  • OEAEE and OEI have 24 hours to reject or ask questions about the request
  • If no objections are expressed within 24 hours, support contractor will create the alias
alias instructions
Alias Instructions

Individual Filing the Request: Tracey Westfield

EPA Federal Account Manager Name: Tracey Westfield

EPA Federal Account Manager Phone Number: 202-564-5586

EPA Federal Account Manager Email:Westfield.Tracey@epa.gov

EPA Server: public

TSSMS Account Name: lawsregs/regstat/

Alias to be added or removed:http://www.epa.gov/regstat/

Action: create alias

Additional Alias Names:

Additional Notes: This is a request for an alias on a folder within the LAWSREGS TSSMS. The folder name is "regstat". That folder currently has one "placeholder" index page, but it'll be populated with a lot more files soon. The new Reg Stat website is under development and currently on a staging server, but I want to have the alias ready once we migrate the files to the "regstat" folder.

managing aliases
Managing Aliases
  • Linux is case-sensitive
  • Aliases will be granted for lowercase letters only
  • If you have more than one alias for your site, must identify a primary alias: http://www.epa.gov/cgi-bin/SPA/selectalias
  • Consider removing all aliases other than the primary alias (critical for consistent linking and WebCMS publication)
  • If the target site for your alias is moved or deleted, remember to update or remove your alias (use the Alias request form in the Web Guide)
  • OEI periodically reviews orphaned aliases and deletes them
impact on search stats
Impact on Search / Stats
  • Some search engines do not recognize symlinks as the same file (e.g., Northern Light) – they will display each alias as a new site
  • Google search should reconcile aliases and display only one page (not 100% sure, though)
  • Analog statistics for each alias is collected separately www.epa.gov/water, www.epa.gov/ow, www.epa.gov/OW
  • Maxamine tries to aggregate statistics for multiple aliases, but does not always know when a new alias is created or one removed
dns aliases
DNS Aliases
  • Resource record in the Domain Name System (DNS) that specifies that the domain name is an alias for another domain
  • Used to create URLs for dedicated servers
  • Can have more than one DNS entry per server
  • Obtained during the ADC process
dns alias
DNS Alias


  • IP address:
  • Server name: kestrel.rtpnc.epa.gov
  • DNS alias entries:
    • intrawiki.epa.gov
    • intrablog.epa.gov
    • nationaldialogue.epa.gov
  • Common Uses of Redirects
    • Redirect users away from a discontinued server
    • Load balancing
    • Display error pages for removed sites
    • Ensure old links still work when pages are moved or renamed
    • Allow users to use an abbreviated or more memorable URL
  • Types of Redirects Used at EPA:
    • Client-side redirects using redirect code
    • Server-side redirects using .htaccess file
    • NOTE: We don’t use the rewrite rule in the Apache config file
client side redirects
Client-Side Redirects
  • Used to redirect users from one server to an application or Website on another server
  • Use the web browser to redirect users to the new URL
  • Redirect code is read in the metadata tag field
  • Created and managed by the content owner
  • Directions and sample redirect code: http://yosemite.epa.gov/OEI/webguide.nsf/create/alias#dynamic
  • All bookmarks to the content will be displayed as the destination URL not the requested URL
client side redirects1
Client-Side Redirects
  • Steps in creating a redirect for your site or application:
    • Create a new TSSMS account or a directory under an existing TSSMS account
    • Request an alias for that TSSMS account or directory
    • Place redirect code inside the new TSSMS account or directory
  • Example:
    • Create new TSSMS account “MYAPPLIC” (www.epa.gov/myapplic)
    • Request alias “www.epa.gov/myapplication” to go to (www.epa.gov/myapplic)
    • Write redirect code for www.epa.gov/myapplic to go to http://cfpub.epa.gov/myapplication
  • Effect:
    • User enters http://www.epa.gov/myapplication
    • Browser reads www.epa.gov/myapplication and sends user to www.epa.gov/myapplic
    • Host location redirects user to http://cfpub.epa.gov/myapplication
client side redirect code
Client-Side Redirect Code
  • An example of a redirect page is epa.gov/npdes/, which uses an HTML redirect to send readers to cfpub.epa.gov/npdes/ as follows:

<HTML> <HEAD> <meta http-equiv="refresh" content="0" URL=http://cfpub.epa.gov/npdes/"> </HEAD> </HTML>

  • This particular code does not incorporate a delay
  • To incorporate a delay, change the value of the content tag (For example, content="3" would provide a three second delay, which would allow you to display a transfer message)
htaccess redirect
.htaccess Redirect
  • Used to redirect users from a URL to a page or directory on either the same or different server
  • Place configuration directives in a text file called .htaccess
  • Place the .htaccess file in the directory to be configured
  • If the configuration is to be applied to the entire site, place the .htaccess file in the root directory of your site (/public/data/TSSMS/web)
  • The directives will be applied to the directory with the .htaccess file and all subdirectories thereof
other uses of htaccess
Other Uses of .htaccess
  • Custom 404 Pages
  • Password-Protected Directories
  • IP-Protected Directories
  • For more information, see Leann Spradling’s “Using Apache .htaccess Files” presentation from the March 2007 Web Workgroup Meeting (Potomac Yard) (http://intranet.epa.gov/webgroup/meetings/03-07/agenda.html)
htaccess redirection
.htaccess Redirection
  • Place an .htaccess file in your root directory with this directive in the file:

Redirect Code /path URL

  • The “code” is optional
  • Possible codes include:
    • 301: Moved Permanently
    • 302: Temporarily Moved (default)
    • 303: Other

Create a redirect to files on a different server:

Redirect /sample01/old.html http://yosemite.epa.gov/sample01/new.html

  • Place .htaccess file under: /public/data/sample01/web/
  • Redirects any user who requests www.epa.gov/sample01/old.html to yosemite.epa.gov/sample01/new.html

Create a redirect to files on the same server:

Redirect /sample01/old.html http://www.epa.gov/sample01/new.html

  • Place .htaccess file under: /public/data/sample01/web
  • Redirects any user who requests www.epa.gov/sample01/old.html to www.epa.gov/sample01/new.html

Use a site alias (symlink) in the redirect

    • “sample” is an alias to “/public/data/sample01”

Redirect /sample/old.html http://www.epa.gov/sample/new.html

  • Place the .htaccess file in the /public/data/sample01/web
  • Redirects any user who requests www.epa.gov/sample01/old.html to www.epa.gov/sample01/new.html
redirect match
Redirect Match
  • Allows you to redirect multiple files with regular expressions

redirectmatch /air(.*) /reg5oair$1

  • Tells the server "if the request is /air, followed by anything else, remember the anything else. Then go to reg50air, and put the anything else after that.
  • This expression would redirect users who enter http://www.epa.gov/region5/air/glakes/ to content located at http://www.epa.gov/reg5oair/glakes/
stacking directives
Stacking Directives
  • There can only be one .htaccess file per directory
  • All directives for the directory must be in that one file, including:
    • Redirection
    • Password Protection
    • 404 Error
    • IP Protection
htaccess problems
.htaccess Problems
  • Precedence
    • Applied in the order they are found by the web server
    • If there is a conflict, the .htaccess file in the subdirectory will take precedence when a file is requested from that subdirectory
  • Syntax Errors
    • Instructions depend on correct syntax
    • Might not render content if syntax error (HTTP 500 error)
  • Webserver Load
    • If there is an .htaccess file in a directory, Apache must check all the directories above it for other .htaccess files that may apply
avoiding problems
Avoiding Problems
  • Test in staging and again when go to production
  • Ensure .htaccess files are world-readable
  • Use the webguide documentation
  • Consider if an .htaccess file is truly the best solution
    • Consider using an HTML redirect page instead
  • Minimize the number of .htaccess files in a site
  • Minimize the number of directives used
  • Maintain .htaccess files – remove outdated directives
  • Comment your .htaccess files for future reference
  • Keep track of existing .htaccess files to avoid conflicts
  • Web Guide: Customize A Web Areahttp://yosemite.epa.gov/oei/webguide.nsf/customize
  • Web Guide: Create or Remove an Aliashttp://yosemite.epa.gov/OEI/webguide.nsf/create/alias
  • 2007 Web Workgroup Presentation on .htaccess fileshttp://intranet.epa.gov/webgroup/meetings/03-07/agenda.html
  • Apache Tutorial on .htaccess files http://httpd.apache.org/docs/2.0/howto/htaccess.html