buildx: [bug] Error: failed to solve: rpc error: code = Unknown desc = content digest sha256:...: not found

Summary

This error occurs randomly, and causes a build to fail when otherwise it would have succeeded. On re-running the exact same build, the error goes away.

Environment

docker-buildx version: standalone binary downloaded from https://github.com/docker/buildx/releases/download/v0.2.2/buildx-v0.2.2.linux-amd64 (sha256 5c31e171440213bb7fffd023611b1aaa7e0498162c54cb708c2a8abe3679717e)

Docker engine version:

Server: Docker Engine - Community
 Engine:
  Version:          18.09.6
  API version:      1.39 (minimum version 1.12)
  Go version:       go1.10.8
  Git commit:       481bc77
  Built:            Sat May  4 01:59:36 2019
  OS/Arch:          linux/amd64
  Experimental:     false

How to reproduce

Unfortunately, I have not found a way to reproduce it reliably. However it does not seem to be related to the contents of the Dockerfile, since I have reproduced it (accidentally) with two completely unrelated Dockerfiles.

Based on my understanding of the error message, it appears that --load is required to reproduce.

Here is the output of the most recent occurrence:

+ /home/sh/bin/docker-buildx build --load --build-arg user=sh --build-arg uid=1002 --build-arg docker_guid=999 -t dev -
[+] Building 11.1s (54/54) FINISHED
 => [internal] load .dockerignore                                                               0.0s
 => => transferring context: 2B                                                                 0.0s
 => [internal] load build definition from Dockerfile                                            0.1s
 => => transferring dockerfile: 2.30kB                                                          0.0s
 => [internal] load metadata for docker.io/library/alpine:latest                                0.4s
 => [1/49] FROM docker.io/library/alpine@sha256:ca1c944a4f8486a153024d9965aafbe24f5723c1d5c02f  0.0s
 => => resolve docker.io/library/alpine@sha256:ca1c944a4f8486a153024d9965aafbe24f5723c1d5c02f4  0.0s
 => CACHED [2/49] RUN apk update                                                                0.0s
 => CACHED [3/49] RUN apk add openssh                                                           0.0s
 => CACHED [4/49] RUN apk add bash                                                              0.0s
 => CACHED [5/49] RUN apk add bind-tools                                                        0.0s
 => CACHED [6/49] RUN apk add curl                                                              0.0s
 => CACHED [7/49] RUN apk add docker                                                            0.0s
 => CACHED [8/49] RUN apk add g++                                                               0.0s
 => CACHED [9/49] RUN apk add gcc                                                               0.0s
 => CACHED [10/49] RUN apk add git                                                              0.0s
 => CACHED [11/49] RUN apk add git-perl                                                         0.0s
 => CACHED [12/49] RUN apk add make                                                             0.0s
 => CACHED [13/49] RUN apk add python                                                           0.0s
 => CACHED [14/49] RUN apk add openssl-dev                                                      0.0s
 => CACHED [15/49] RUN apk add vim                                                              0.0s
 => CACHED [16/49] RUN apk add py-pip                                                           0.0s
 => CACHED [17/49] RUN apk add file                                                             0.0s
 => CACHED [18/49] RUN apk add groff                                                            0.0s
 => CACHED [19/49] RUN apk add jq                                                               0.0s
 => CACHED [20/49] RUN apk add man                                                              0.0s
 => CACHED [21/49] RUN cd /tmp && git clone https://github.com/AGWA/git-crypt && cd git-crypt   0.0s
 => CACHED [22/49] RUN apk add go                                                               0.0s
 => CACHED [23/49] RUN apk add coreutils                                                        0.0s
 => CACHED [24/49] RUN apk add python2-dev                                                      0.0s
 => CACHED [25/49] RUN apk add python3-dev                                                      0.0s
 => CACHED [26/49] RUN apk add tar                                                              0.0s
 => CACHED [27/49] RUN apk add vim                                                              0.0s
 => CACHED [28/49] RUN apk add rsync                                                            0.0s
 => CACHED [29/49] RUN apk add less                                                             0.0s
 => CACHED [30/49] RUN pip install awscli                                                       0.0s
 => CACHED [31/49] RUN curl --silent --location "https://github.com/weaveworks/eksctl/releases  0.0s
 => CACHED [32/49] RUN curl https://dl.google.com/dl/cloudsdk/channels/rapid/downloads/google-  0.0s
 => CACHED [33/49] RUN curl -L -o /usr/local/bin/kubectl https://storage.googleapis.com/kubern  0.0s
 => CACHED [34/49] RUN curl -L -o /usr/local/bin/kustomize  https://github.com/kubernetes-sigs  0.0s
 => CACHED [35/49] RUN apk add ruby                                                             0.0s
 => CACHED [36/49] RUN apk add ruby-dev                                                         0.0s
 => CACHED [37/49] RUN gem install bigdecimal --no-ri --no-rdoc                                 0.0s
 => CACHED [38/49] RUN gem install kubernetes-deploy --no-ri --no-rdoc                          0.0s
 => CACHED [39/49] RUN apk add npm                                                              0.0s
 => CACHED [40/49] RUN npm config set unsafe-perm true                                          0.0s
 => CACHED [41/49] RUN npm install -g yarn                                                      0.0s
 => CACHED [42/49] RUN npm install -g netlify-cli                                               0.0s
 => CACHED [43/49] RUN apk add libffi-dev                                                       0.0s
 => CACHED [44/49] RUN pip install docker-compose                                               0.0s
 => CACHED [45/49] RUN apk add shadow sudo                                                      0.0s
 => CACHED [46/49] RUN echo '%wheel ALL=(ALL) NOPASSWD: ALL' > /etc/sudoers                     0.0s
 => CACHED [47/49] RUN useradd -G docker,wheel -m -s /bin/bash -u 1002 sh                       0.0s
 => CACHED [48/49] RUN groupmod -o -g 999 docker                                                0.0s
 => CACHED [49/49] WORKDIR /home/sh                                                             0.0s
 => ERROR exporting to oci image format                                                        10.5s
 => => exporting layers                                                                         0.6s
 => => exporting manifest sha256:97c8dedb84183d0d87b6c930b12e1b9396bb81fd9c6587fe2fbb9ae092d30  0.0s
 => => exporting config sha256:ef15b3f6a374fd494a0a586f7b33ac9435953460776e268b20f2eee5f14def6  0.0s
 => => sending tarball                                                                          9.6s
 => importing to docker                                                                         0.0s
------
 > exporting to oci image format:
------
Error: failed to solve: rpc error: code = Unknown desc = content digest sha256:ef15b3f6a374fd494a0a586f7b33ac9435953460776e268b20f2eee5f14def65: not found
Usage:
  /home/sh/bin/docker-buildx build [OPTIONS] PATH | URL | - [flags]

Aliases:
  build, b

Flags:
      --add-host strings         Add a custom host-to-IP mapping (host:ip)
      --build-arg stringArray    Set build-time variables
      --cache-from stringArray   External cache sources (eg. user/app:cache, type=local,src=path/to/dir)
      --cache-to stringArray     Cache export destinations (eg. user/app:cache, type=local,dest=path/to/dir)
  -f, --file string              Name of the Dockerfile (Default is 'PATH/Dockerfile')
  -h, --help                     help for build
      --iidfile string           Write the image ID to the file
      --label stringArray        Set metadata for an image
      --load                     Shorthand for --output=type=docker
      --network string           Set the networking mode for the RUN instructions during build (default "default")
      --no-cache                 Do not use cache when building the image
  -o, --output stringArray       Output destination (format: type=local,dest=path)
      --platform stringArray     Set target platform for build
      --progress string          Set type of progress output (auto, plain, tty). Use plain to show container output (default "auto")
      --pull                     Always attempt to pull a newer version of the image
      --push                     Shorthand for --output=type=registry
      --secret stringArray       Secret file to expose to the build: id=mysecret,src=/local/secret
      --ssh stringArray          SSH agent socket or keys to expose to the build (format: default|<id>[=<socket>|<key>[,<key>]])
  -t, --tag stringArray          Name and optionally a tag in the 'name:tag' format
--target string Set the target build stage to build.