[wpietri]

Could you say more about why your particular service can't tolerate rolling replacement of nodes? You're going to have to rebuild nodes eventually, so it seems to me that you might as well get good at it.

And just to be clear, I'm very willing to believe that your particular legacy setup isn't a good match for cattle-not-pets practices. But I think that's different than saying it's impossible for anybody to bring an immutable approach to things like storage.

[lukeschlather]

The person you're replying to didn't say "replace every node," they said "replace the whole thing."

To give a really silly example, adding a node to a cluster is a configuration change. It wouldn't make sense to destroy the cluster and recreate it to add a new node. There are lots of examples like this where if you took the idea of immutable infrastructure to the extreme it would result in really large wastes of effort.

[wpietri]

Could you please point me at prominent advocates of immutable infrastructure who propose destroying whole clusters to add a node? Because from what I've seen, that's a total misunderstanding.

[lukeschlather]

As I said, it's a silly example just to highlight an extreme. In between there are more fluid examples. I don't think it's that ridiculous to propose destroying and recreating the cluster in its entirety when you're deploying a new node image. However as you say I'm not sure anyone would advocate that except in specific circumstances.

On the other hand, while my suggestion of doing it to add a node sounds ridiculous I'm sure there are circumstances in which it's not only understandable but necessary, due to some aspect of the system.

[wpietri]

I'm saying it's not even an extreme, in that I don't believe what people are calling "immutable infrastructure" includes that.

If your biggest objection to an idea is that you can make up a silly thing that sounds like it might be related, I'm not understanding why we need to have this discussion. I'd like to focus on real issues, thanks.

[lukeschlather]

I'm not objecting categorically to anything. I think that immutable infrastructure is a spectrum, and depending on your needs you may have just about everything immutably configured, or almost nothing. I just don't think it's so black and white as "you should always use immutable infrastructure."

I also think it's a cool idea to destroy the entire cluster just to add a node, and it sounds ridiculous but also like there's some circumstances where it makes perfect sense.

[wpietri]

Again, do you have a citation for the notion that it's a spectrum? The original post that coined the term doesn't talk about it that way, and neither do the other resources I found in a quick search. As I see it, it's binary: when you need to change something on a server, you either tinker with the existing server or you replace the server with a fresh-built one that conforms to the new desire.

[notacoward]

Wow, look at those goalposts go! If you make enough exceptions to allow incremental change, then "immutable" gets watered down to total meaninglessness. That's not an interesting conversation. This conversation is about configuration management, which is still needed in a "weakly immutable" world.

[wpietri]

Again, could you please point me at notable advocates of immutable infrastructure proposing the approach you take such exception to? And note that I'm not proposing any exceptions.