Back in May 2017 I blogged about creating a simple library which supports passing correlation IDs between ASP.NET Core micro-services. The library came about because of a basic requirement we had at work to pass an identifier between related services to enable more useful error logging. By passing an identifier from the first service, through to any further services it then calls; if an exception occurs, we can quickly search for the entire history of that request across the distributed environment.
Since I released that first version to NuGet I have been staggered by the download stats. According to NuGet it now has nearly 27,000 downloads at the time of writing this post. I never really expected it to be used that heavily so this is a really pleasant surprise. I’m very pleased that something I’ve created is helping others with a similar requirement. It is a little daunting to think that so many people are dependent on that library in their code!
Three months ago I released version 2.0 of the library which added the concept of a CorrelationContext. This was a something I’d been considering almost immediately after completing version 1.0. An issue with v1 was that I’d chosen to set the TraceIdentifier on the HttpContext to match the correlation ID being passed in via the request headers. In controllers, where the HttpContext is accessible, this was not a major issue since the value of TraceIdentifier could then be read and used in logging. However, to use the correlation ID elsewhere, the only way to access it was via the IHttpContextAccessor. This isn’t registered in ASP.NET Core by default and so for some users of the library meant they would have to register it to make full use of the correlation ID.
I based my version 2 changes on the HttpContext and HttpContextAccessor in ASP.NET Core and this seems to have worked quite nicely so far. This required a breaking change for the library since it needed to register some services to support the new CorrelationContext.
Today I released version 2.1 of the library. This version adds two new configuration options that can be set when registering the middleware. One of these options came as a result of a GitHub issue requesting that it be possible to disable updating the TraceIdentifier with the correlation ID. This is now possible since the ID is passed around in the CorrelationContext and I needn’t rely on the HttpContext. To avoid breaking changes I added the option with it default setting behaving as it did before. I may look to change this default in the next major release.
I took the opportunity to add another new option that determines if the correlation ID should be matched to the TraceIdentifier or whether it should be a GUID in situations where an ID is not present in the header. For some users I can see this being useful and at work I’m considering the move to a GUID for our correlation ID.
A final change I was able to incorporate came as a result of another feature request via the projects GitHub issues. In this case it was to include the configured correlation ID header name on the CorrelationContext. This resulted in the first external PR on the project which I was very happy to receive. Thanks to Julien for his contribution.
I hope that people using the library are happy with these changes. As ever I’m happy to take feedback and ideas via GitHub if there are use cases that it doesn’t currently support.
UPDATE: It seems I wasn’t as careful as I thought about breaking changes. One did slip through in this release as I updated the interface and implementation for the ICorrelationContextFactory to support the new property on the context. If you’re consuming the library this is not something you generally need to access but if you’re mocking for unit testing it’s possible this will break there. Apologies! Turns out it’s harder than you think avoid breaking changes when released publicly!
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