oak app image layer caching

RyanPaesschesooneVintecc

Hi,

We deploy OAK apps to cameras in the field, some connected only over LTE, and we're looking for a way to reduce transfer size. Each .oakapp is ~1.9G, and even when only our application code changes, the entire file is re-sent.

Inspecting the .oakapp, I can see the per-build-stage layers. I expected the large dependency layer to be stable across builds, but its hash changes every time. Comparing the largest layer (lower-1.tar.lz4, ~1.6G) between two builds of identical source (v2.8.2 vs v2.8.2_rev1), the uncompressed contents are byte-for-byte identical — a diff of tar tv output shows same path, same size, only the mtime differs (e.g. 14:55 vs 15:14). Since mtime is stored in the tar header, the compressed layer and its hash differ, so the full 1.6G re-transfers despite no real change.

Questions:

Does oakctl support delta/content-addressed layer transfer, so unchanged layers are skipped when deploying to a device?
Can the build be made reproducible (e.g. normalized mtimes in the tar step) so unchanged layers keep a stable hash?
Is moving stable dependencies into a pre-baked private base image the recommended pattern to keep only the app layer changing between releases?

Any guidance or planned improvements here would be very helpful.

Kind regards,
Ryan

Oskar-Luxonis

Hey RyanPaesschesooneVintecc - oakctl app install currently transfers the new .oakapp package as a whole. There is no layer-level delta/content-addressed transfer option exposed for reusing unchanged package layers already on the device.

The layer cache applies primarily when building on the device. For installed package updates, the practical workaround is to move stable, heavy dependencies into a custom ARM64 base image and keep only frequently changing application code in the app layer. That is the recommended pattern for this use case, especially over LTE. You can configure a private base image in oakapp.toml; see the OAK App configuration docs and base-image guide.

Your mtime observation also explains why the dependency layer hash changes despite identical files. There is not currently a documented setting to normalize archive mtimes or make .oakapp output reproducible in this way. I’ll pass this on as a valuable improvement request, since it directly affects OTA bandwidth for large apps.

You may also try oakctl app build --optimized, which can reduce package size, though it will not provide delta transfer.

Thanks,
Oskar

RyanPaesschesooneVintecc

Hey Oskar,

We managed to use our own base image for an oakapp. Are there any updates on the cached layers feature? We are willing to help test new features in the field.

kind regards

Ryan

Oskar-Luxonis

Hey RyanPaesschesooneVintecc - thanks for testing this.

There is no update for cached or delta layer transfer. oakctl app install sends the complete .oakapp, and the base image is included in that package.

Thanks,
Oskar