Environment:
SharePoint 2010 Enterprise
3 WFE’s each with Query Roles
2 App Servers with 1 Dedicated Indexer
Error in Event Viewer:
Event ID: 8313
SharePoint Web Services Round Robin Service Load Balancer Event: EndpointFailure
Process Name: w3wp
Process ID: 5948
AppDomain Name: /LM/W3SVC/303076968/ROOT-1-129634027688317155
AppDomain ID: 2
Service Application Uri: urn:schemas-microsoft-com:sharepoint:service:767f7d712e064db3bb8945d9d42d0e12#authority=urn:uuid:f7625c7a33924a9981c0206f8bf0054a&authority=https://applicationserver:32844/Topology/topology.svc
Active Endpoints: 3
Failed Endpoints:1
Affected Endpoint: http://applicationserver:32843/767f7d712e064db3bb8945d9d42d0e12/SearchService.svc
Error in Diagnostic Logs:
Internal server error exception: System.ServiceModel.ServerTooBusyException: The HTTP service located at http://applicationserver:32843/767f7d712e064db3bb8945d9d42d0e12/SearchService.svc is too busy. —> System.Net.WebException: The remote server returned an error: (503) Server Unavailable. at System.Net.HttpWebRequest.GetResponse() at System.ServiceModel.Channels.HttpChannelFactory.HttpRequestChannel.HttpChannelRequest.WaitForReply(TimeSpan timeout)
Troubleshooting Steps:
I tried to access the web service that SharePoint was trying to get to via the browser and noticed that it was reporting a 503 error as reported in the Diagnostic Logs. Then I hopped onto IIS on the affected servers and looked at the SharePoint Web Services web application (IIS) in search for a corresponding Service Application GUID that matched. The application didn’t exist on either of the application servers so that would cause the EndpointFailure as reported in the Event Viewer logs. I then double checked the Services on Server page for the application servers to make sure that the search services were turned on as having these turned on would provision the web services. They were all started which threw a little confusion my way but with some hints from this forum post, I went ahead and stopped/started the Search Query and Site Settings Service. After a little while, assuming that some timer jobs had to run, the Service Application with the missing GUID showed up in IIS and the error stopped appearing in the Event logs.
Summarized Solution:
1. Go to your Services on Server page in Central Administration.
2. Stop and Start the Search Query and Site Settings Service on each affected server as reported in the Event Viewer or SharePoint Diagnostic Logs.
The SharePoint Swiss Army Knife 
Thanks for the info Henry, that did stop the errors.
We have seen this problem a couple times, the first time we ended up just recreating the Search App, but then it came back about a month later.
We do have a case open with MS, but no idea on root cause (why does the GUID dissapear). Will update if they come back with anything earth shattering.
Bryan,
Any update ffrom MS regarding this issue
Thanks
K
Thank you… it did fixed my problem…. Thank god that i found this blog…!!
Hello I am facing the same error on my prod servers.
It is Multi server farm.
I am also facing intermitent search issue.
And it shows error on the servers where “Search Query and Site Settings Service” is not running and since begining it is like that only.
Your help will be much appreciated.
Thanks,
SP~
Thanks, was seeing the same errors, stopped and started the search query… fingers are crossed 🙂
This is my problem as well, but none of this worked to fix it. I’ve restarted the services, restarted the machine, reprovisioned search, reprovisioned the proxy, using both the GUI and then using Powershell, all but rebuilt the environment… no dice. I also tried changing the permissions for the performance counters as indicated in antoher post similar so that the timer job service could write perfs… nada… Running sp2013, 2 WFE’s one CA/App server dedicated to index front ends query.
Same thing than RogerBoone here, when i tried to reset the Index… All my problems begins at this time. VERY VERY VERY DISAPPOINTED ABOUT SHAREPOINT SEARCH 2013
Thanks for the information & Solution.
That really works for me.
Hi everyone, so after 2 yrs, I guess someone fixed the issue, found the root cause? I see crawler slowing down from very promising crawl rate of +80 items/sec. down to < 1 item/sec after an hour, sometimes 2 hrs crawl. Noticed Event 8313 on my content farm as well.