Docker experimental build still uses a system cache after mounting a different cach for pip installs

问题

I was following this StackOverflow answer (https://stackoverflow.com/a/58021389/11268971) to get my Docker build image process to use a cache directory with package wheels for pip install. However, when I switched from (suggested in the SO answer)

# syntax = docker/dockerfile:experimental
FROM python:3.7
RUN --mount=type=cache,target=/root/.cache/pip pip install -r requirements.txt

to

# syntax = docker/dockerfile:experimental
FROM python:3.7
RUN --mount=type=cache,target=/home/my_username/new_dir_i_created_just_for_docker_builds pip install --no-index --find-links=/home/my_username/new_dir_i_created_just_for_docker_builds -r requirements.txt

Docker buildkit started failing to mount the new directory, it still looks for packages in the old directory I mounted /root/.cache/pip.

I tried clearing the cache with docker builder prune and its different flags. To no avail.

Any ideas how I can get this to work?

P. S. I decided to create my own directory under my user, since installing /root/.cache/pip would regularly stop (docker build would download packages from the Net, instead of installing cached versions) after the first 4 or so builds or 1 day after initial cache mount. My hypothesis is that /root/.cache/pip was overwritten or invalidated.

EDIT: My Dockerfile

# syntax = docker/dockerfile:experimental
FROM python:3.7
ADD . /app
WORKDIR /app
RUN --mount=type=cache,target=/home/my_username/new_dir_i_created_just_for_docker_builds pip install --no-index --find-links=/home/my_username/new_dir_i_created_just_for_docker_builds -r requirements.txt
ENV CONTAINER_ID=""
ENV HOST=""
ENV PORT=""
ENV MODELPATH=""
CMD "python" "/app/model.py" $CONTAINER_ID $HOST $PORT $MODELPATH

My Docker build logs:

#1 [internal] load .dockerignore
#1 transferring context: 2B done
#1 DONE 0.0s

#2 [internal] load build definition from Dockerfile
#2 transferring dockerfile: 468B done
#2 DONE 0.1s

#3 resolve image config for docker.io/docker/dockerfile:experimental
#3 DONE 3.0s

#4 docker-image://docker.io/docker/dockerfile:experimental@sha256:de85b2f3a...
#4 CACHED

#5 [internal] load metadata for docker.io/library/python:3.7
#5 DONE 0.0s

#7 [internal] load build context
#7 transferring context: 1.00kB done
#7 DONE 0.0s

#6 [stage-0 1/4] FROM docker.io/library/python:3.7
#6 CACHED

#8 [stage-0 2/4] ADD . /app
#8 DONE 1.2s

#9 [stage-0 3/4] WORKDIR /app
#9 DONE 0.2s

#10 [stage-0 4/4] RUN --mount=type=cache,target=/home/my_username/new_dir_i_created_just_for_docker_builds ...
#10 3.110 Looking in links: /home/my_username/new_dir_i_created_just_for_docker_builds/
#10 3.119 ERROR: Could not find a version that satisfies the requirement absl-py==0.9.0 (from -r /app/requirements.txt (line 1)) (from versions: none)
#10 3.119 ERROR: No matching distribution found for absl-py==0.9.0 (from -r /app/requirements.txt (line 1))
#10 ERROR: executor failed running [/bin/sh -c pip install --no-index --find-links=/home/my_username/new_dir_i_created_just_for_docker_builds -r /app/requirements.txt]: runc did not terminate sucessfully
------
 > [stage-0 4/4] RUN --mount=type=cache,target=/home/my_username/new_dir_i_created_just_for_docker_builds pip install --no-index --find-links=/home/rytis/test-cont-cache/ -r /app/requirements.txt:
------
failed to solve with frontend dockerfile.v0: failed to solve with frontend gateway.v0: rpc error: code = Unknown desc = failed to build LLB: executor failed running [/bin/sh -c pip install --no-index --find-links=/home/my_username/new_dir_i_created_just_for_docker_builds/ -r /app/requirements.txt]: runc did not terminate sucessfully

来源：https://stackoverflow.com/questions/63046991/docker-experimental-build-still-uses-a-system-cache-after-mounting-a-different-c