Images and the Registry
KraftCloud uses a registry to store the images used to instantiate apps
from. At a high level, a user uses kraft
to build and push an image to
the registry, and then to ask the controller to start an app from it. The
steps involved are illustrated in this diagram:
- build: The app is built, locally, according to a
Dockerfile
. - pkg: The app is packaged, locally, into an OCI image.
- push: The OCI image is pushed to the KraftCloud registry.
- create: Your app is instantiated from the image accoring to a
Kraftfile
.
The simplest way to run this workflow is to use kraft cloud deploy
, which subsumes
all of these steps into a single command. Under the hood, the deploy command uses other
sub-commands to carry out the work of the different steps, though we wonβt bother you
with them here π. Note that the service group in the diagram is KraftCloudβs mechanism
to connect apps to the Internet; read more about that in this guide.
In this guide weβll use a Python app as a running example to show a number of workflows:
- How to create an image and launch an instance from it.
- How to create an image and launch multiple instances from it.
- How to launch instances from an existing image.
Finally, we will explain the use of Dockerfile
and Kraftfile
files in the process,
as well as what a runtime means.
Letβs get started!
Workflow1: Create an Image and an Instance from it
We will start with the simplest workflow: create an image from a Python app,
as per the Python app guide, and start an instance from it, all
with a single kraft cloud deploy
command:
The output should be similar to:
This command uses the Kraftfile
and Dockerfile
files in the directory to build
an image named http-python312@sha256:278cb8b1...
, package it, push it to the registry
and request KraftCloud to start an instance named
http-python312-ma2i9
from it (causing the controller in the diagram at the top to
fetch the image from the registry in order to start the instance).
You can see your images by running the following command:
You should see output similar to
And you can remove an image from the registry via:
Workflow2: Create an Image and Multiple Instances from it
For the next workflow, weβll once again use kraft cloud deploy
but this time weβll use the -R
flag
to start multiple instances from it:
You can check that it worked by listing all instances with:
Note there are 3 running instances in total: the one we created plus the 2 replicas.
Workflow3: Create Instances from an Existing Image
In this final workflow, weβll take the image we created above and use it to start new instances
using the kraft cloud instance
command:
Thatβs it, now you have a shiny new instance from the image you had previously created.
Dockerfiles, Kraftfiles and Runtimes
On KraftCloud, the process of building images is guided by a Dockerfile
,
and the process of deploying the resulting image by a Kraftfile
.
Letβs use once again our Python running example. The directory:
contains the following Kraftfile
:
The file is pretty simple, stating what the cmd
for starting the application should
be, that a Dockerfile
should be used to build its root filesystem, and that the
python3.12
runtime should be used. On KraftCloud, a runtime is a base image that
contains the (minimal) code needed for the application (in this case the Python interpreter)
to run; your application code is then overlayed on top of it during the packaging step.
The Dockerfile
itself for our app looks as follows:
If youβre familiar with Dockerfiles
there shouldnβt be anything too
mysterious in them, other than by default we use FROM scratch
to
ensure that the resulting images are as lean as possible. To add your
appβs code to the build modify the COPY
commands as needed.
All guides on KraftCloud, and the examples they rely on
underneath come with Kraftfile
s and Dockerfile
s for you to easily get started.
Learn More
- The
kraft cloud
CLI reference. - KraftCloudβs REST API reference.