The main reason for specialisation is efficiency. The selection of the contents and ordering of layers has an effect on how quickly the can be rebuilt/updated,

The main reason for specialisation is efficiency. The selection of the contents and ordering of layers has an effect on how quickly the can be rebuilt/updated, how big they need to be, how much deduplication you can get between images etc. A few years ago I wrote up a scheme (which wasn't pursued) for automatic image construction[0]. The first half of the writeup enumerated a bunch of problems with relying purely on Dockerfiles. [0] https://docs.google.com/document/d/1M2PJ_h6GzviUNHMPt7x-5POUaadcvK3ZNT9QEGDZhPk/edit https://docs.google.com/document/d/1M2PJ_h6GzviUNHMPt7x-5POU...