How could I make something like this? I know how to place text inside a shape but not this. Could it be vector and scalable?
Not possible to generate something like this in photoshop or illustrator using native tools. Depending on your requirements and skills you could check out creating the shape and circles in a different application or programming language and exporting that as an svg or similar in to Illustrator/Photoshop and colouring it or fine tuning it from there.
I put together a proof of concept script on CodePen here: http://codepen.io/marblegravy/pen/cfAHi
Which I did based on a discussion here: https://mathematica.stackexchange.com/questions/40334/generating-visually-pleasing-circle-packs
Okay I'm not totally sure, but this might help:
Similar process can be repeated for the outer circle; this time masking being done by a circular selection. Hope it helps! :)
This is actually doable in Illustrator (through advance scripting). Luckily, this dude has done just what we required here.
Make sure you download the scripts, and then restart Illustrator.
You might also need a few extra steps for color variation of each circle. But that's not much of a problem.