Emilio Murillo Hernandez

Troubleshooting your Akamaized domain with Fiddler

Blog Post created by Emilio Murillo Hernandez Employee on Apr 21, 2016

Months ago I created this guide using Microsoft Word, mainly to help a customer I had on a CCare case.


I thought it was a shame for it to be eventually lost, so I better share the information here


Fiddler is a free web debugging proxy.   It is useful as it let the user make captures in real time of what is happening at a web surfing session.  You can save a file and share it with colleagues or support people.


There are reference to other topics such as Akamai Pragma headers, use of HAR files, etc, that already have posts about them right here at Akamai Community.




Installation and initial setup


1.       Download Fiddler from the Fiddler Website  http://www.telerik.com/download/fiddler and install the appropriate version according to .NET version installed on your PC  ( if you do not know, check this article https://support.microsoft.com/en-us/kb/318785 )
NOTE for MAC users:   At the time of this writing (apr 2016), the install link above says:   
Need a Linux or Mac build?  --  Check Out the Alpha Build --- Mac Note: The WinForms framework on Mac is almost unusably buggy. Your best bet is to run Fiddler inside a Linux or Windows Virtual Machine and point the Mac's proxy settings at that.


2.       In order to view useful columns (the default ones are too basic) at the Fiddler capture,  copy the file CustomRules.js to     C:\Users\yourWindowsUserName\Documents\Fiddler2\Scripts   .     The file is attached to this blog post. Scroll down all the way, just before the comments section, to find it

These custom rules also include the addition of Akamai Pragma headers to the requests.


3.       (Re)start Fiddler




Capturing a web surfing session@@


Start fiddler and make sure you completed the previous section,  and that the capturing is on:


To capture SSL traffic please do the following:

  1. Click Tools > Fiddler Options > HTTPS.
  2. Click the Decrypt HTTPS Traffic box.

Fiddler Options -- Decrypt HTTPS Traffic

Once you visit any website, the capture will start populating.  If website is “Akamaized”, such as www.akamai.com, the custom columns will have useful information for troubleshooting, such as “Machine IP” or “Request ID”.

When you click on one of the capture lines, and have the  “Inspectors” Tab selected, you can see the header information, too (subtab “Headers” must be chosen at both Request and Response)




Once you are ready to reproduce the issue you need to troubleshoot, it is advisable to clean the sessions (every line in the capture is called a session) by choosing

Edit  -  Remove  -  All Sessions


Once you are done with the issue reproduction you can produce a Fiddler capture by saving everything to a SAZ file (the default extension for Fiddler saves).

This is done as follows:

File  –  Save  –  All Sessions


This file you can re-load later for analysis, and also send it to colleagues or to Akamai support/account team for more help.


To load the file simply do   File  –  Load archive  and locate the SAZ file.

It may be a good idea to stop capturing traffic so no more lines get added to the screen while you are doing



Filtering session lines


Sometimes  you want to center the attention on specific hostnames or URLs.

For instance, If you quickly want to have Fiddler highlight sessions that contain .js  objects





Once “Find Sessions” is clicked, the result looks like this:




The second alternative offers more options, and makes use of actual filters.

You have to locate the Filters tab, mark the checkbox, configure what you need among the various options, and then run the filter.  Here below is an example of having sessions with hostname = *akamai.com   and URLs that contain  .js



The result is seen as follows




Importing and loading HAR files


If you have a HAR file you created, or someone sent one to you, that HAR file can actually be imported and viewed into Fiddler



Spoofing to other domains


Sometimes you require to test against Akamai staging network or the origin itself.  Fiddler can be used to do this and capture the session at the same time