There is a person that has been in the company for 6 years and worked on a bunch of building blocks that are now being replaced with, what we consider, more modern alternatives to improve the way we work.
This person does not see anything wrong with the old ways of doing things and has said so a few times. For the last 6 months, he has been really angry and communication style has become super aggressive, there is a lot of passive-aggressive comments as well.
We have tried explaining why we're doing these changes, showing the benefits, where it will get us, etc. But this person's attitude has been to shutdown and silo themselves more and more. It's looking like he's in a 1-person subteam inside our team.
Do you have any suggestions about how to overcome this situation? Have you had this situation in your team?
Aside from legitimate technical concerns, which you did not mention, from that person point of view, he/she was likely the expert, the go to person to understand how stuff worked, or could be implemented, and suddenly he/she will be relegated to a maintenance mode or worse be let go.
That might not be true, but that is surely how that person feels.
So depending on the exact circumstances, you have to reassure him/her by taking concrete actions, like making him/her responsible of a key element of the new architecture, so that this person will feel empowered and useful in the future.
To be blunt, even if the situation is better for the company or product roadmap, in the end, most people don't care. The normal reaction of normal people in face of change, is to consider how it will affect THEM first, they don't necessarily take into account the bigger picture. So you cannot convince them with rationale and objective elements how it will improve the life of everybody else.
You need to get to the _why_ behind his emotions and responses, and you need to assume positive intent as you do so. Why does he think the old ways of working are better? Why doesn't he agree with the changes being made? Are the benefits being touted from the new ways of doing things actually beneficial for him?
It's really easy for teams, especially those with drastic age differences, to trash/isolate the "old guy" for being a luddite/lifer. Nobody wants to go through that!
Also, if he built the building blocks that your team is now replacing, he may just be too attached to the work that he put in. Letting go and being okay with your work being replaced is really tough; it was tough for me! This could be a growth opportunity for him...if he sees it that way _and_ if you manage him into it appropriately.
Do you have regular 1-on-1's with this person? If not, then you should.
Now, if you've tried all of these things and he still isn't willing to at least _try_ to get with the changes, then it might be time for him to find somewhere that's a better fit for the work he wants to do. Attitudes like his can kill good teams over time. This should be the last resort, though, and you shouldn't waver about it if it comes to that.