Unable to open App permission (Central Admin->Apps->App Management->App permission)

Question

I am unable to open App permission (Central Admin->Apps->App Management->App permission).

It shows error

The remote server returned an error (503) service unavailable.

I am also unable to add SharePoint Hosted app to my site content.

I am attaching the logs below

WcfSendRequest: RemoteAddress: 'URL..>/20a7c2a85126418789dbb9ac0d43cd0a/AppMng.svc' Channel: 'Microsoft.SharePoint.AppManagement.IAppManagementServiceApplication' Action: 'http://schemas.microsoft.com/sharepoint/soap/IAppManagementServiceApplication/GetAppManagementDatabaseMap' MessageId: 'urn:uuid:8fc309ab-9d57-44d3-9126-35665d66a307' 3b234a9d-e2cf-80cd-6ead-cf70deb3fb8b

12/11/2015 13:22:29.72 w3wp.exe (0x1C1C)                       0x5854  SharePoint Foundation                 General                                       abihl      Medium               Exception returned from back end service. System.ServiceModel.ServerTooBusyException: The HTTP service located at URL..>/20a7c2a85126418789dbb9ac0d43cd0a/AppMng.svc is unavailable.  This could be because the service is too busy or because no endpoint was found listening at the specified address. Please ensure that the address is correct and try accessing the service again later. ---> System.Net.WebException: The remote server returned an error: (503) Server Unavailable.     at System.Net.HttpWebRequest.GetResponse()     at System.ServiceModel.Channels.HttpChannelFactory`1.HttpRequestChannel.HttpChannelRequest.WaitForReply(TimeSpan timeout)     --- End of inner exception stack trace ---    Server stack trace:      at System.ServiceModel.Channels.HttpChannelUtilities.Pr...            3b234a9d-e2cf-80cd-6ead-cf70deb3fb8b

12/11/2015 13:22:29.72*               w3wp.exe (0x1C1C)                       0x5854  SharePoint Foundation                 General                                       abihl      Medium               ...ocessGetResponseWebException(WebException webException, HttpWebRequest request, HttpAbortReason abortReason)     at System.ServiceModel.Channels.HttpChannelFactory`1.HttpRequestChannel.HttpChannelRequest.WaitForReply(TimeSpan timeout)     at System.ServiceModel.Channels.RequestChannel.Request(Message message, TimeSpan timeout)     at System.ServiceModel.Channels.SecurityChannelFactory`1.SecurityRequestChannel.Request(Message message, TimeSpan timeout)     at System.ServiceModel.Channels.ServiceChannel.Call(String action, Boolean oneway, ProxyOperationRuntime operation, Object[] ins, Object[] outs, TimeSpan timeout)     at System.ServiceModel.Channels.ServiceChannelProxy.InvokeService(IMethodCallMessage methodCall, ProxyOperationRuntime operation)     at System.ServiceModel.Channels.Service...         3b234a9d-e2cf-80cd-6ead-cf70deb3fb8b

12/11/2015 13:22:29.72*               w3wp.exe (0x1C1C)                       0x5854  SharePoint Foundation                 General                                       abihl      Medium               ...ChannelProxy.Invoke(IMessage message)    Exception rethrown at [0]:      at System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage reqMsg, IMessage retMsg)     at System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData& msgData, Int32 type)     at Microsoft.SharePoint.AppManagement.IAppManagementServiceApplication.GetAppManagementDatabaseMap()     at Microsoft.SharePoint.AppManagement.AppManagementServiceApplicationProxy.<>c__DisplayClass2.<GetScaleOutDatabaseMap>b__0(IAppManagementServiceApplication channel)     at Microsoft.SharePoint.Administration.SPServiceApplicationProxyBase`1.ExecuteOnChannel(Boolean requireDelegation, Action`1 codeBlock) 3b234a9d-e2cf-80cd-6ead-cf70deb3fb8b

12/11/2015 13:22:29.72 OWSTIMER.EXE (0x9678)                              0x9CC8 SharePoint Foundation                 Monitoring                                    b4ly        High       Leaving Monitored Scope (EnsureListItemsData). Execution Time=10.8955           9f1d499d-728e-80cd-6ead-cf378876e529

12/11/2015 13:22:29.72 w3wp.exe (0x1C1C)                       0x5854  SharePoint Foundation                 General                                       8nca       Medium               Application error when access /_admin/AllAppPrincipals.aspx, Error=The remote server returned an error: (503) Server Unavailable. 

Answer 1

Looks like your App management service is not working/unavailable.

Since you don't have more information about the issue you can follow the steps below:

First check if you have a App Management Service, go Central Admin > Application Management > Service Applications > Manage Service Applications.

If you don't have this service you can create a new one, in the ribbon go to the Service Application TAB > New > App Management Service.

If you already have one, check if the database server and application pool is working, and check if your managed account have the right permissions on the appMng database.

Also check if the service is started on Central Admin > System Settings > Servers > Manage Services on Server and check if the App Management Service is started.

Answer 2

503 error is indication of either App Pool under which ApMangement services is running is stopped / hanged or AppManagement Service is not running on central admin.

1. go to IIS >sites>under SharePoint web Services > check the App Management Service End(it should be a guid). get the app pool from there and restart the app pool then try.
2. or go to central admin > manage services on server > make sure App management Services is running. May be you can stop and start it.
3. check the event log and see if there is any other services throwing the error. some time security token services cause this error.