Building Microservices: Designing Fine-Grained Systems

by Sam Newman

So how do we fix things here? Well, we need to make a change in two places. First, we need to stop the finance code from reaching into the line item table, as this table really belongs to the catalog code, and we don’t want database integration happening once catalog and finance are services in their own rights. The quickest way to address this is rather than having the code in finance reach into the line item table, we’ll expose the data via an API call in the catalog package that the finance code can call. This API call will be the forerunner of a call we will make over the wire, as we see in Figure 5-3. Figure 5-3. Post removal of the foreign key relationship At this point it becomes clear that we may well end up having to make two database calls to generate the report. This is correct. And the same thing will happen if these are two separate services. Typically concerns around performance are now raised. I have a fairly easy answer to those: how fast does your system need to be? And how fast is it now? If you can test its current performance and know what good performance looks like, then you should feel confident in making a change. Sometimes making one thing slower in exchange for other things is the right thing to do, especially if slower is still perfectly acceptable.

Foreign Key breaking in MS