kaniko - Build Images In Kubernetes
kaniko is a tool to build container images from a Dockerfile, inside a container or Kubernetes cluster.
kaniko doesn't depend on a Docker daemon and executes each command within a Dockerfile completely in userspace. This enables building container images in environments that can't easily or securely run a Docker daemon, such as a standard Kubernetes cluster.
kaniko is meant to be run as an image, gcr.io/kaniko-project/executor
.
We do not recommend running the kaniko executor binary in another image, as it might not work.
If you are interested in contributing to kaniko, see DEVELOPMENT.md and CONTRIBUTING.md.
How does kaniko work?
The kaniko executor image is responsible for building an image from a Dockerfile and pushing it to a registry. Within the executor image, we extract the filesystem of the base image (the FROM image in the Dockerfile). We then execute the commands in the Dockerfile, snapshotting the filesystem in userspace after each one. After each command, we append a layer of changed files to the base image (if there are any) and update image metadata.
Known Issues
kaniko does not support building Windows containers.
Demo
Using kaniko
To use kaniko to build and push an image for you, you will need:
- A build context, aka something to build
- A running instance of kaniko
kaniko Build Contexts
kaniko currently supports local directories, Google Cloud Storage and Amazon S3 as build contexts. If using a GCS or S3 bucket, the bucket should contain a compressed tar of the build context, which kaniko will unpack and use.
To create a compressed tar, you can run:
tar -C <path to build context> -zcvf context.tar.gz .
Then, copy over the compressed tar into your bucket. For example, we can copy over the compressed tar to a GCS bucket with gsutil:
gsutil cp context.tar.gz gs://<bucket name>
Use the --context
flag with the appropriate prefix to specify your build context:
Source | Prefix |
---|---|
Local Directory | dir://[path to directory] |
GCS Bucket | gs://[bucket name]/[path to .tar.gz] |
S3 Bucket | s3://[bucket name]/[path to .tar.gz] |
If you don't specify a prefix, kaniko will assume a local directory.
For example, to use a GCS bucket called kaniko-bucket
, you would pass in --context=gs://kaniko-bucket/path/to/context.tar.gz
.
Running kaniko
There are several different ways to deploy and run kaniko:
Running kaniko in a Kubernetes cluster
Requirements:
- Standard Kubernetes cluster (e.g. using GKE)
- Kubernetes Secret
Kubernetes secret
To run kaniko in a Kubernetes cluster, you will need a standard running Kubernetes cluster and a Kubernetes secret, which contains the auth required to push the final image.
To create the secret, first you will need to create a service account in the Google Cloud Console project you want to push the final image to, with Storage Admin
permissions.
You can download a JSON key for this service account, and rename it kaniko-secret.json
.
To create the secret, run:
kubectl create secret generic kaniko-secret --from-file=<path to kaniko-secret.json>
The Kubernetes Pod spec should look similar to this, with the args parameters filled in:
apiVersion: v1
kind: Pod
metadata:
name: kaniko
spec:
containers:
- name: kaniko
image: gcr.io/kaniko-project/executor:latest
args: ["--dockerfile=<path to Dockerfile>",
"--context=gs://<GCS bucket>/<path to .tar.gz>",
"--destination=<gcr.io/$PROJECT/$IMAGE:$TAG>"]
volumeMounts:
- name: kaniko-secret
mountPath: /secret
env:
- name: GOOGLE_APPLICATION_CREDENTIALS
value: /secret/kaniko-secret.json
restartPolicy: Never
volumes:
- name: kaniko-secret
secret:
secretName: kaniko-secret
This example pulls the build context from a GCS bucket. To use a local directory build context, you could consider using configMaps to mount in small build contexts.
Running kaniko in gVisor
Running kaniko in gVisor provides an additional security boundary.
You will need to add the --force
flag to run kaniko in gVisor, since currently there isn't a way to determine whether or not a container is running in gVisor.
docker run --runtime=runsc -v $(pwd):/workspace -v ~/.config:/root/.config \
gcr.io/kaniko-project/executor:latest \
--dockerfile=<path to Dockerfile> --context=/workspace \
--destination=gcr.io/my-repo/my-image --force
We pass in --runtime=runsc
to use gVisor.
This example mounts the current directory to /workspace
for the build context and the ~/.config
directory for GCR credentials.
Running kaniko in Google Container Builder
To run kaniko in GCB, add it to your build config as a build step:
steps:
- name: gcr.io/kaniko-project/executor:latest
args: ["--dockerfile=<path to Dockerfile>",
"--context=dir://<path to build context>",
"--destination=<gcr.io/$PROJECT/$IMAGE:$TAG>"]
kaniko will build and push the final image in this build step.
Running kaniko locally
Requirements:
We can run the kaniko executor image locally in a Docker daemon to build and push an image from a Dockerfile.
- Load the executor image into the Docker daemon by running:
make images
- Run kaniko in Docker using
run_in_docker.sh
:
./run_in_docker.sh <path to Dockerfile> <path to build context> <destination of final image>
Pushing to Different Registries
kaniko uses Docker credential helpers to push images to a registry.
kaniko comes with support for GCR and Amazon ECR, but configuring another credential helper should allow pushing to a different registry.
Pushing to Amazon ECR
The Amazon ECR credential helper is built in to the kaniko executor image. To configure credentials, you will need to do the following:
- Update the
credHelpers
section of config.json with the specific URI of your ECR registry:
{
"credHelpers": {
"aws_account_id.dkr.ecr.region.amazonaws.com": "ecr-login"
}
}
You can mount in the new config as a configMap:
kubectl create configmap docker-config --from-file=<path to config.json>
- Create a Kubernetes secret for your
~/.aws/credentials
file so that credentials can be accessed within the cluster.
To create the secret, run:
kubectl create secret generic aws-secret --from-file=<path to .aws/credentials>
The Kubernetes Pod spec should look similar to this, with the args parameters filled in:
apiVersion: v1
kind: Pod
metadata:
name: kaniko
spec:
containers:
- name: kaniko
image: gcr.io/kaniko-project/executor:latest
args: ["--dockerfile=<path to Dockerfile>",
"--context=s3://<bucket name>/<path to .tar.gz>",
"--destination=<aws_account_id.dkr.ecr.region.amazonaws.com/my-repository:my-tag>"]
volumeMounts:
- name: aws-secret
mountPath: /root/.aws/
- name: docker-config
mountPath: /kaniko/.docker/
restartPolicy: Never
volumes:
- name: aws-secret
secret:
secretName: aws-secret
- name: docker-config
configMap:
name: docker-config
Additional Flags
--snapshotMode
You can set the --snapshotMode=<full (default), time>
flag to set how kaniko will snapshot the filesystem.
If --snapshotMode=time
is set, only file mtime will be considered when snapshotting (see
limitations related to mtime).
--build-arg
This flag allows you to pass in ARG values at build time, similarly to Docker. You can set it multiple times for multiple arguments.
--single-snapshot
This flag takes a single snapshot of the filesystem at the end of the build, so only one layer will be appended to the base image.
--reproducible
Set this flag to strip timestamps out of the built image and make it reproducible.
--tarPath
Set this flag as --tarPath=<path>
to save the image as a tarball at path instead of pushing the image.
--target
Set this flag to indicate which build stage is the target build stage.
--no-push
Set this flag if you only want to build the image, without pushing to a registry.
--insecure
Set this flag if you want to connect to a plain HTTP registry. It is supposed to be used for testing purposes only and should not be used in production!
--skip-tls-verify
Set this flag to skip TLS certificate validation when connecting to a registry. It is supposed to be used for testing purposes only and should not be used in production!
Debug Image
The kaniko executor image is based off of scratch and doesn't contain a shell.
We provide gcr.io/kaniko-project/executor:debug
, a debug image which consists of the kaniko executor image along with a busybox shell to enter.
You can launch the debug image with a shell entrypoint:
docker run -it --entrypoint=/busybox/sh gcr.io/kaniko-project/executor:debug
Security
kaniko by itself does not make it safe to run untrusted builds inside your cluster, or anywhere else.
kaniko relies on the security features of your container runtime to provide build security.
The minimum permissions kaniko needs inside your container are governed by a few things:
- The permissions required to unpack your base image into it's container
- The permissions required to execute the RUN commands inside the container
If you have a minimal base image (SCRATCH or similar) that doesn't require permissions to unpack, and your Dockerfile doesn't execute any commands as the root user, you can run Kaniko without root permissions. It should be noted that Docker runs as root by default, so you still require (in a sense) privileges to use Kaniko.
You may be able to achieve the same default seccomp profile that Docker uses in your Pod by setting seccomp profiles with annotations on a PodSecurityPolicy to create or update security policies on your cluster.
Comparison with Other Tools
Similar tools include:
All of these tools build container images with different approaches.
img
can perform as a non root user from within a container, but requires that
the img
container has RawProc
access to create nested containers. kaniko
does not actually create nested containers, so it does not require RawProc
access.
orca-build
depends on runc
to build images from Dockerfiles, which can not
run inside a container (for similar reasons to img
above). kaniko
doesn't
use runc
so it doesn't require the use of kernel namespacing techniques.
However, orca-build
does not require Docker or any privileged daemon (so
builds can be done entirely without privilege).
umoci
works without any privileges, and also has no restrictions on the root
filesystem being extracted (though it requires additional handling if your
filesystem is sufficiently complicated). However it has no Dockerfile
-like
build tooling (it's a slightly lower-level tool that can be used to build such
builders -- such as orca-build
).
buildah
requires the same privileges as a Docker daemon does to run, while
kaniko
runs without any special privileges or permissions.
FTL
and Bazel
aim to achieve the fastest possible creation of Docker images
for a subset of images. These can be thought of as a special-case "fast path"
that can be used in conjunction with the support for general Dockerfiles kaniko
provides.
Community
kaniko-users Google group
To Contribute to kaniko, see DEVELOPMENT.md and CONTRIBUTING.md.
Limitations
mtime and snapshotting
When taking a snapshot, kaniko's hashing algorithms include (or in the case of
--snapshotMode=time
, only use) a file's
mtime
to determine
if the file has changed. Unfortunately there is a delay between when changes to a
file are made and when the mtime
is updated. This means:
- With the time-only snapshot mode (
--snapshotMode=time
), kaniko may miss changes introduced byRUN
commands entirely. - With the default snapshot mode (
--snapshotMode=full
), whether or not kaniko will add a layer in the case where aRUN
command modifies a file but the contents do not change is theoretically non-deterministic. This does not affect the contents which will still be correct, but it does affect the number of layers.
Note that these issues are currently theoretical only. If you see this issue occur, please open an issue.