Bazel: How to extend existing docker image? - bazel

Question

I know in Dockerfile I can extend existing docker image using:
FROM python/python
RUN pip install request
But how to extend it in bazel?
I am not sure if I should use container_import, but with that I am getting the following error:
container_import(
name = "postgres",
base_image_registry = "some.artifactory.com",
base_image_repository = "/existing-image:v1.5.0",
layers = [
"//docker/new_layer",
],
)
root#ba5cc0a3f0b7:/tcx# bazel build pkg:postgres-instance --verbose_failures --sandbox_debug
ERROR: /tcx/docker/postgres-operator/BUILD.bazel:12:17: in container_import rule //docker/postgres-operator:postgres:
Traceback (most recent call last):
File "/root/.cache/bazel/_bazel_root/2f47bbce04529f9da11bfed0fc51707c/external/io_bazel_rules_docker/container/import.bzl", line 98, column 35, in _container_import_impl
"config": ctx.files.config[0],
Error: index out of range (index is 0, but sequence has 0 elements)
ERROR: Analysis of target '//pkg:postgres-instance' failed; build aborted: Analysis of target '//docker/postgres-operator:postgres' failed
INFO: Elapsed time: 0.209s
INFO: 0 processes.
FAILED: Build did NOT complete successfully (1 packages loaded, 2 targets configured)

Answer 1

container_import is the correct rule to import an existing image. However, all it does is import, it doesn't pull it from anywhere. I think you're looking for container_pull instead, which will pull an image from a repository and then automatically use container_import to translate it for other rules_docker rules.
To add a new layer, use container_image, with base set to the imported image and tars set to the additional files you want to add. Or, if you want to add things in other formats, see the docs for alternates to tars (like debs or files).
Putting it all together, something like this in your WORKSPACE:
container_pull(
name = "postgres",
registry = "some.artifactory.com",
repository = "existing-image",
tag = "v1.5.0",
)
and then this in a BUILD file:
container_image(
name = "postgres_plus",
base = "#postgres//image",
tars = ["//docker/new_layer"],
)
The specific problem you're running into is that container_pull.layers isn't for adding new layers, it's for specifying the layers of the image you're importing. You could import those some other way (http_archive, check in the tar files, etc) and then specify them all by hand instead of using container_pull if you're doing something unusual.