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How to get the instance index of a web role or worker role - Windows Azure

When we have one or more instances of a specific web role or worker role in the cloud, there are moments when we want to know from the code how many instances we have of the specific type or the index of current instance.
The total number of instances can be obtained using
RoleEnvironment.Roles[i].Value.Instance.Count
To be able to detect the index of the current instance we need to parse the id of the role instance. Usually the id of the current instance ends with the index number. Before this number we have ‘.’ character if the instance is on the cloud or ‘_’ when we are using emulator.
Because of this we will end with the following code when we need to get the index of the current instance:
int currentIndex = 0;
string instanceId = RoleEnvironment.CurrentRoleInstace.Id;
bool withSuccess = int.TryParse(instanceId.Substring(instanceId.LastIndexOf(".") + 1, out currentIndex));
if( !withSuccess )
{
  withSuccess = int.TryParse(instanceId.Substring(instanceId.LastIndexOf("_") + 1, out currentIndex));
}
Take into account that when you increase and decrease the number of instances, there are situation when you can end up with the following name of the instances:
  • […].0
  • […].1
  • […].3
  • […].4
Two is missing because when we decreased the number of instances from 5 to 4, that instance was stopped.

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