Throwing exceptions the right way

You can become a serverless blackbelt. Enrol to my 4-week online workshop Production-Ready Serverless and gain hands-on experience building something from scratch using serverless technologies. At the end of the workshop, you should have a broader view of the challenges you will face as your serverless architecture matures and expands. You should also have a firm grasp on when serverless is a good fit for your system as well as common pitfalls you need to avoid. Sign up now and get 15% discount with the code yanprs15!

Use ReSharper? Notice every time ReSharper sees code like this:

catch (Exception ex)
{
    // some exception handling, or logging here
    throw ex;
}

it complains, and tells you to get rid of the ex for the reason ‘Exception rethrow possibly intended’?

The reason ReSharper is warning you about an ‘exception rethrow’ is that when you rethrow an exception it replaces the stack trace of the original exception with the current location. So if you print the stack trace further up the code you will not be able to see the statement which caused the exception in the first place!

For this reason, you should ALWAYS use this instead:

catch (Exception ex)
{
    // exception handling
    throw;
}

Handling multiple exceptions

Further on exception handling, if your code might throw multiple types of exceptions and you want to handle the exceptions differently then you can build up a hierarchy of catch clauses from the most specific (SqlException e.g.) at the top, to the least specific (Exception) at the bottom like this:

try
{
    // do something that can might throw an exception
}
catch (SqlException sqlEx)
{
    // retry on timeout or deadlock for example?
}
catch (Exception ex)
{
    // handle more generic exception
}
finally
{
    // put any clean up operations here
}

It’s worth noting that, if you are catching the more general exceptions further up the chain your exception handling code for more specific types of exception lower down the list will never be called! But fortunately tools like ReSharper will warn you first :-)

Another thing you might want to consider is to wrap the built-in exception types into a custom Exception type and maybe use an enum to categorise the different exceptions into well defined types that your application understands (e.g. ServerError, FeedError, DatabaseError, etc.).

In the case of WCF services, you can also specify fault contracts for each operation and in your catch clauses on the server side wrap all exceptions into faults so when exceptions happen they don’t fault your channel. For more on WCF error handling and fault conversion, have a look at this article.

Liked this article? Support me on Patreon and get direct help from me via a private Slack channel or 1-2-1 mentoring.
Subscribe to my newsletter


Hi, I’m Yan. I’m an AWS Serverless Hero and I help companies go faster for less by adopting serverless technologies successfully.

Are you struggling with serverless or need guidance on best practices? Do you want someone to review your architecture and help you avoid costly mistakes down the line? Whatever the case, I’m here to help.

Hire me.


Skill up your serverless game with this hands-on workshop.

My 4-week Production-Ready Serverless online workshop is back!

This course takes you through building a production-ready serverless web application from testing, deployment, security, all the way through to observability. The motivation for this course is to give you hands-on experience building something with serverless technologies while giving you a broader view of the challenges you will face as the architecture matures and expands.

We will start at the basics and give you a firm introduction to Lambda and all the relevant concepts and service features (including the latest announcements in 2020). And then gradually ramping up and cover a wide array of topics such as API security, testing strategies, CI/CD, secret management, and operational best practices for monitoring and troubleshooting.

If you enrol now you can also get 15% OFF with the promo code “yanprs15”.

Enrol now and SAVE 15%.


Check out my new podcast Real-World Serverless where I talk with engineers who are building amazing things with serverless technologies and discuss the real-world use cases and challenges they face. If you’re interested in what people are actually doing with serverless and what it’s really like to be working with serverless day-to-day, then this is the podcast for you.


Check out my new course, Learn you some Lambda best practice for great good! In this course, you will learn best practices for working with AWS Lambda in terms of performance, cost, security, scalability, resilience and observability. We will also cover latest features from re:Invent 2019 such as Provisioned Concurrency and Lambda Destinations. Enrol now and start learning!


Check out my video course, Complete Guide to AWS Step Functions. In this course, we’ll cover everything you need to know to use AWS Step Functions service effectively. There is something for everyone from beginners to more advanced users looking for design patterns and best practices. Enrol now and start learning!