To add layer caching to kaniko, I added two flags: --cache and
--use-cache.
If --use-cache is set, then the cache will be used, and if --cache is
specified then that repo will be used to store cached layers. If --cache
isn't set, a cache will be inferred from the destination provided.
Currently, caching only works for RUN commands. Before executing the
command, kaniko checks if the cached layer exists. If it does, it pulls
it and extracts it. It then adds those files to the snapshotter and
append a layer to the config history. If the cached layer does not exist, kaniko executes the command and
pushes the newly created layer to the cache.
All cached layers are tagged with a stable key, which is built based off
of:
1. The base image digest
2. The current state of the filesystem
3. The current command being run
4. The current config file (to account for metadata changes)
I also added two integration tests to make sure caching works
1. Dockerfile_test_cache runs 'date', which should be exactly the same
the second time the image is built
2. Dockerfile_test_cache_install makes sure apt-get install can be
reproduced
gometalinter is broken @ HEAD, and I looked into why that was. During
that process, I remembered that we took the linting scripts from
skaffold, and found that in skaffold gometalinter was replaced with
GolangCI-Lint:
https://github.com/GoogleContainerTools/skaffold/pull/619
The change made linting in skaffold faster, so I figured instead of
fixing gometalinter it made more sense to remove it and replace it with
GolangCI-Lint for kaniko as well.
As mentioned in #346, if only ENTRYPOINT is set in a stage then any
CMD inherited from a parent should be cleared.
If both entrypoint and cmd are set then nothing should change.
I added a function and unit test to review the config file after building a stage
which clears out config.Cmd if ENTRYPOINT was declared but CMD wasn't.
I also added an integration test to make sure this works, which should
be tested by the preexisting container-diff --metadata test.
While looking into #345, we were seeing the error:
Error: error building image: chmod /etc/mtab: operation not permitted
during extraction of `amazonlinux:1`. I looked into why kaniko couldn't
extract this file properly, and found that it already existed as a
symlink pointing to /proc/mounts, which returned an error when we tried
to run chmod on it.
Confusingly, in the image the /etc/mtab is a regular file, not a
symlink.
I can think of two ways to solve this problem:
1. Whitelist /etc/mtab so that whatever already exists in the system
is used
2. Check if a regular file already exists, and hasn't been extracted yet,
before extracting
I went with option 1 because for option 2 we'd have to keep a list of
all files that had been extracted in memory.
Refactoring builds by stage will make it easier to generate cache keys
for layers, since the stageBuilder type will contain everything required
to generate the key:
1. Base image with digest
2. Config file
3. Snapshotter (which will provide a key for the filesystem)
4. The current command (which will be passed in)
This will return a string representaiton of the current filesystem to be
used with caching.
Whenever a file is explictly added (via ADD or COPY), it will be stored
in "added" in the LayeredMap. The file will map to a hash created by
CacheHasher (which doesn't take into account mtime, since that will be
different with every build, making the cache useless)
Key() will returns a sha of the added files which will be used in
determining the overall cache key for a command.
CacheCommand returns true if the command should be cached. Currently,
it's only true for RUN but can be added to ADD/COPY later on (these are
different since the contents of files for ADD/COPY need to be included
in the cache key generation).
I also changed CreatedBy to String so that we can log each command
before cache extraction or regular execution takes place.
The bug in #329 occurred because of a bug in matchSources, where the
filepath wasn't absolute, so the source "/kaniko-bug/*" wasn't being
matched to the file "kaniko-bug/test-file"
To fix this, I added logic for making filepaths absolute and added to
the unit test for the function to test that it works.
Extracting the layers of the filesystem in order will make it easier to
extract cached layers and deal with hardlinks.
This PR implements extracting in order and adds an integration tests to
make sure hardlinks are extracted properly.
It also fixes two bugs I found when extracting symlinks:
1. We'd get a "file exists" error when trying to symlink to an existing
file with a whiteout later in the layer tarball
2. We'd get a "file exists" error when trying to create a symlink from a
file that was created in a prior layer (perhaps as a regular file or as
a symlink pointing to someting else)
To fix both of these, we resolve all symlinks in a layer at the end. I
also added logic to delete any existing paths before creating the
symlink.
I was seeing an error with our cloudbuild triggers where the tagged
:latest version of image wasn't the same as the :commit version, even
though it was created via 'docker tag image:commit image:latest'.
I'm not sure why this would be happening, but for now building each
image separately should hopefully fix this error.
Priya Wadhwa
Tejal Desai
Kartik Verma
Sebastian Jackel
Sharif Elgamal