Request failed with HTTP status 503 Server Error

Problem: When 100's of users ae trying to access Reporting services report then, SSRS throws error as below : "Request failed with HTTP status 503 Server Error" and how to resolve this error

Solution:

From experience, this issue can be caused by multiple reasons

Problem might be related to:

1 - TCP/IP Port Exhaustion: When a client initiates a TCP/IP socket connection to a server, the client typically connects to a specific port on the server and requests that the server respond to the client over a short-lived TCP or UDP port. The default range of short-lived ports used by client applications is 1025 through 5000. Under certain conditions, it is possible that the available ports in the default range are exhausted.

2 - If you are using any custom assembly method in any of your report (say for example PrivateFontCollection class or anything else), if yes then you might want to review that

3 - Change MaxActiveReqForOneUser from its default value of 20 to 9999 and problem could be resolved

<Add Key="MaxActiveReqForOneUser" Value="9999"/>

Please Note: As such MaxActiveReqForOneUser configuration setting specifies the maximum number of reports that one user can process at the same time (Default is 20). Note that most requests process very quickly so it is unlikely that a single user will have more than 20 open connections at any given time. Further this setting is ignored for report servers that run in SharePoint integrated mode.

http://technet.microsoft.com/en-us/library/ms157273.aspx

So technically as such, changing MaxActiveReqForOneUser property  from default value of 20 to 9999 should not make any difference, but with one of the client, by changing this property, we have tested on 2 report server and 503 error issue was resolved.

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