I'm currently working with a customer who is undergoing an initiative to expose some of their line of business applications to external partners and SAAS applications and as part of this we have been looking at using the Windows Azure Service Bus. For the first part of the project we were focused on some synchronous request response scenarios where an external application would use the Service Bus relay functionality to get data from some internal applications.

When we were looking at the operational monitoring side of the solution it was obvious that although most of the normal server monitoring capabilities would be required for the on premise components we would have to look at new approaches to validate that the operation of the service from outside of the organization was working as expected.

A number of months ago one of my colleagues Elton Stoneman wrote about an approach I have introduced with a number of clients in the past where we implement a diagnostics service in each service component we build. This service would allow us to make a call which would flex some of the working parts of the system to prove it was working within any SLA. This approach is discussed on the following article:

http://geekswithblogs.net/EltonStoneman/archive/2011/12/12/the-value-of-a-diagnostics-service.aspx

In our solution we wanted to take the same approach but we had to consider that the service clients were external to the service. We also had to consider that by going through Windows Azure Service Bus it's not that easy to make most of your standard monitoring solutions just give you an easy way to do this.

In a previous article I have described how you can use BizTalk 360 to monitor things using a custom extension to the Web Endpoint Manager and I felt that we could use this approach to provide an excellent way to monitor our service bus endpoint. The previous article is available on the following link:

http://geekswithblogs.net/michaelstephenson/archive/2012/09/12/150696.aspx

The Monitoring Solution

BizTalk 360 currently has an easy way to hook up the endpoint manager to a url which it will then call and if a successful response is returned it then considers the endpoint to be in a healthy state. We would take advantage of this by creating an ASP.net web page which would be called by BizTalk 360 and behind this page we would implement the functionality to call the diagnostics service on our Service Bus endpoint. The ASP.net page could include logic to work out how to handle the response from the diagnostics service. For example if the overall result of the diagnostics service was successful but the call to the diagnostics service was longer than a certain amount of time then we could return an error and indicate the service is taking too long.

The following diagram illustrates the monitoring pattern.

The diagnostics service which is hosted in the line of business application allows us to ping a simple message through the Azure Service Bus relay to the WCF services in the LOB application and we they get a response back indicating that the service is working fine.

To implement this I used the exact same approach I described in my previous post to create a custom web page which calls the diagnostics service and then it would return an HTTP response code which would depend on the error condition returned or a 200 if it was successful.

One of the limitations of this approach is that the competing consumer pattern for listening to messages from service bus means that you cannot guarantee which server would process your diagnostics check message but with BizTalk 360 you could simply add multiple endpoint checks so that it could access the individual on-premise web servers directly to ensure that each server is working fine and then check that messages can also be processed through the cloud.

Conclusion

It took me about 15 minutes to get a proof of concept of this up and running which was able to monitor our web services which had been exposed via Windows Azure Service Bus. I was then able to inherit all of the monitoring benefits of BizTalk 360 to provide an enterprise class monitoring solution for our cloud enabled API.