Query App Insights customEvent custom dimensions

On a recent project using MassTransit to produce and event based data exchange system, for tracing I thought it would be really sensible to add the serialized message to app insights custom events – turned out to be really helpful, making tracing so much easier.

I already had a mass transit message IConsumeObserver observer to log any exceptions so adding the consumed message with its message content was relatively simple. Ultimately the TelemetryClient TrackEvent operation accepts an IDictionary<string, string> to record custom dimensions so all that was required was a dimensions builder:

1 public interface IBuildCustomDimensions 2 { 3 Dictionary<string, string> Build<T>(T message); 4 } 5 6 public class CustomDimensionsBuilder : IBuildCustomDimensions 7 { 8 public Dictionary<string, string> Build<T>(T message) 9 { 10 return CreateDefaultMessageProperties(message); 11 } 12 13 private Dictionary<string, string> CreateDefaultMessageProperties<T>(T message) 14 { 15 if (!(message is ISessionMessage)) return null; 16 17 var session = message as ISessionMessage; 18 return new Dictionary<string, string>() 19 { 20 { "SessionId", session.SessionId.ToString() }, 21 { "Message", JsonConvert.SerializeObject(message) } 22 }; 23 } 24 } 25

Pretty simple, with our own session Id as a dimension for easy querying along with the JSON serialized the message as another dimension.

When logged the custom dimensions result was displaying as expected (ignoring the complete lack of imagination in the made up message of course):

1 { 2 "SessionId":"4bd715d5-bfbc-47c2-a10a-2738f5795627", 3 "Message":"{\"Value1\":123, \"Value2\":456}" 4 }

The beauty part of this along with our session identifier meant we could easily trace all messages through for a change. But the power of App Insights querying meant we could easily also read and query using message content – just remember to use “tostring” on the serialized message before parsing – like so:

1 customEvents 2 | sort by timestamp desc 3 | extend Value1 = parsejson(tostring(customDimensions.Message)).Value1 4 | limit 5 5

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