using --no-cache still uses CACHED layers and host cache

[FernandoMiguel]

$ ~/.docker/cli-plugins/docker-buildx bake --no-cache -f kimi.yml
[+] Building 2.1s (13/21)
 => [internal] load build definition from buildx-builder                                                                                                                                                                                 0.0s
 => => transferring dockerfile: 36B                                                                                                                                                                                                      0.0s
 => [internal] load .dockerignore                                                                                                                                                                                                        0.0s
 => => transferring context: 35B                                                                                                                                                                                                         0.0s
 => resolve image config for docker.io/docker/dockerfile:experimental                                                                                                                                                                    0.4s
 => CACHED docker-image://docker.io/docker/dockerfile:experimental@sha256:9022e911101f01b2854c7a4b2c77f524b998891941da55208e71c0335e6e82c3                                                                                               0.0s
 => [internal] load metadata for docker.io/library/alpine:latest                                                                                                                                                                         0.0s
 => [internal] load metadata for docker.io/library/node:8.11-alpine                                                                                                                                                                      0.0s
 => CANCELED [internal] load build context                                                                                                                                                                                               1.0s
 => => transferring context: 14.31MB                                                                                                                                                                                                     1.0s
 => [storage 1/6] FROM docker.io/library/alpine                                                                                                                                                                                  0.0s
 => CACHED [storage 2/6] WORKDIR /var/www                                                                                                                                                                                        0.0s
 => CACHED [storage 3/6] RUN adduser -DHSu 100 nginx -s /sbin/nologin                                                                                                                                                            0.0s
 => [builder 1/8] FROM docker.io/library/node:8.11-alpine                                                                                                                                                                        0.0s
 => CACHED [builder 2/8] WORKDIR /src                                                                                                                                                                                            0.0s
 => ERROR [builder 3/8] RUN --mount=type=cache,target=/var/cache     apk add --update     git                                                                                                                                    1.0s
------
 > [builder 3/8] RUN --mount=type=cache,target=/var/cache     apk add --update     git:
#12 0.775 fetch http://dl-cdn.alpinelinux.org/alpine/v3.6/main/x86_64/APKINDEX.tar.gz
#12 0.786 fetch http://dl-cdn.alpinelinux.org/alpine/v3.6/community/x86_64/APKINDEX.tar.gz
#12 0.788 ERROR: http://dl-cdn.alpinelinux.org/alpine/v3.6/main: Bad file descriptor
#12 0.788 WARNING: Ignoring APKINDEX.84815163.tar.gz: Bad file descriptor
#12 0.805   git (missing):
#12 0.805     required by: world[git]
#12 0.805 ERROR: http://dl-cdn.alpinelinux.org/alpine/v3.6/community: Bad file descriptor
#12 0.805 WARNING: Ignoring APKINDEX.24d64ab1.tar.gz: Bad file descriptor
#12 0.805 ERROR: unsatisfiable constraints:
------
Error: failed to solve: rpc error: code = Unknown desc = executor failed running [/bin/sh -c apk add --update     git]: exit code: 1

github.com/docker/buildx v0.2.2-10-g3f18b65-tp-docker 3f18b65

Client: Docker Engine - Community
Version: 19.03.0-rc2
API version: 1.40
Go version: go1.12.5
Git commit: f97efcc
Built: Wed Jun 5 01:37:53 2019
OS/Arch: darwin/amd64
Experimental: false

Server: Docker Engine - Community
Engine:
Version: 19.03.0-rc2
API version: 1.40 (minimum version 1.12)
Go version: go1.12.5
Git commit: f97efcc
Built: Wed Jun 5 01:42:10 2019
OS/Arch: linux/amd64
Experimental: true
containerd:
Version: v1.2.6
GitCommit: 894b81a4b802e4eb2a91d1ce216b8817763c29fb
runc:
Version: 1.0.0-rc8
GitCommit: 425e105d5a03fabd737a126ad93d62a9eeede87f
docker-init:
Version: 0.18.0
GitCommit: fec3683

[thaJeztah]

Looks similar to moby/moby#38255 (which has some more info/discussion)

[tonistiigi]

This is a bit tricky cause cache mounts are global and not tied to a specific build request. I see how this can be confusing though so hopefully there is a solution.