Declarative vs imperative
Introduction
Our container orchestrator puts a very strong emphasis on being declarative
Declarative:
I would like a cup of tea.
Imperative:
Boil some water. Pour it in a teapot. Add tea leaves. Steep for a while. Serve in a cup.
- Declarative seems simpler at first ...
- ... As long as you know how to brew tea
Declarative vs imperative
What declarative would really be:
I want a cup of tea, obtained by pouring an infusion¹ of tea leaves in a cup.
¹An infusion is obtained by letting the object steep a few minutes in hot² water.
²Hot liquid is obtained by pouring it in an appropriate container³ and setting it on a stove.
³Ah, finally, containers! Something we know about. Let's get to work, shall we?
Did you know there was an ISO standard specifying how to brew tea?
Declarative vs imperative
Imperative systems:
simpler
if a task is interrupted, we have to restart from scratch
Declarative systems:
if a task is interrupted (or if we show up to the party half-way through), we can figure out what's missing and do only what's necessary
we need to be able to observe the system
... and compute a "diff" between what we have and what we want