Comparison
Ephemeral container filesystemvsOverlay filesystem
Ephemeral container filesystem
the uploaded files were there all afternoon and gone after a restart, because they were written inside the container.
The rule that everything a container writes outside a mounted volume is discarded when it stops. It is deliberate — it is what makes a container replaceable — and it is the single most common surprise for an application ported from a virtual machine. It also has a capacity dimension: unbounded local writes fill the node's disk and get the workload evicted, taking well-behaved neighbours with it.
Full entry →Overlay filesystem
the container writes a file and it lands in a thin writable layer on top, leaving the image underneath untouched.
The union mount that stacks read-only image layers and one writable layer into a single filesystem. It is why starting a container does not copy the image, and why a container that writes heavily to its own filesystem gets slow copy-on-write behaviour for files that came from a layer. Anything written there dies with the container, which is the mechanism behind logs and uploads mysteriously vanishing on restart.
Full entry →