How to create my resume with tricky-to-describe projects?

The trick here is to focus on (1) the complexity of the work and (2) the strides you were able to make. Talk about the impact that the microservice architecture would have enabled, and share how it would have interacted with the broader system.

Don't focus on the lack of support you received (certainly not in the resume). You don't want anything in the resume to read as victimization or blaming others. It should focus only on what you achieved.

I highly recommend going through these:

• Explaining Your Experience In A Meaningful Way On A Resume
• What high-impact achievements should a full-stack engineering intern target for a stronger resume?

From my understanding, you weren't able to complete the project, so focus on farming the keywords as the impact is 0. The good news is that you have a lot of solid keywords in there (Node.js, Microservice, Unit Tests) - Make sure that they're all in the resume as well (it will help with the ATS). For the unit tests, name drop the framework you used to write them as well. If you had high unit-test coverage (i.e. 70%+) on your module, you can throw that in to make things even crispier.

As Rahul mentioned, don't throw anybody under the bus in your description. To clarify, here's the delta between what you have in your post vs. what I think would be optimal:

• Bad: Built a Node.js API and microservice with high unit test coverage despite having 0 guidance from senior engineers
• Good: Built a Node.js API and microservice from scratch with 70%+ unit test coverage to serve 100,000+ users

The good part focuses entirely on you (i.e. replaces the "no senior support" part with "from scratch") and throws in some numbers to solidify the achievement.

I recommend this other resume discussion as well (there's even more helpful resources linked there): "Entrepeneur for over 11 years getting back into corporate - How to optimize my resume?"