mirror of
https://github.com/GNS3/gns3-registry.git
synced 2024-12-24 15:06:43 +00:00
119 lines
3.9 KiB
Markdown
119 lines
3.9 KiB
Markdown
# Docker Build System
|
|
|
|
The regular Docker build system has the disadvantage,
|
|
that only the cache system prevents a repetitive rebuild.
|
|
But when running the build in a VM this cache is initially
|
|
empty, resulting in a rebuild of all images on every run.
|
|
This not only increases the CPU load of the VM, but also
|
|
creates a lot of updated Docker images, that differ only
|
|
in the timestamps of the files.
|
|
|
|
This Docker build system wants to improve this situation.
|
|
It rebuilds only, when the base image or the build context
|
|
has changed. There are some other situations, where an
|
|
image needs to be recreated, that are not detected.
|
|
This mainly affects installation packages and external
|
|
files, that got an update. Then a manual trigger is needed.
|
|
|
|
|
|
## Build Tool
|
|
|
|
The `docker_build` tool reads a configuration file and
|
|
then starts building images with `docker buildx build`.
|
|
|
|
If `docker_build` is launched without arguments, it checks
|
|
all configured images for an update of the base image.
|
|
Additionally it checks, if `git` shows an update of
|
|
the directory containing the docker build context.
|
|
When at least one of these conditions is met, the tool
|
|
starts a rebuild of that image.
|
|
|
|
When `docker_build` is run with some image names as
|
|
arguments, then these images are additionally built.
|
|
When using a base image name as an argument, then all
|
|
images with that base image are rebuilt.
|
|
|
|
When using the option -a/--all, all images are forcibly
|
|
rebuild, except those specified on the command line.
|
|
|
|
|
|
## Configuration File
|
|
|
|
The build tool reads a configuration file, by default
|
|
'docker_images', located in the current directory. For each
|
|
target image, it contains its name, its context directory
|
|
and optionally the base image and some build options.
|
|
|
|
The fields are separated by one or more \<tab\> characters.
|
|
Comments start with a `#` as its first field character.
|
|
An empty line or an all-comments line is ignored.
|
|
|
|
A line with only one field is used for build options,
|
|
which are effective from that point until they are redefined.
|
|
This global build option and an optional image specific option
|
|
are combined and sent to the `docker buildx` command.
|
|
|
|
Here an example:
|
|
|
|
```
|
|
# Name Directory [Base Image] [Build Options]
|
|
|
|
--platform=linux/arm64,linux/amd64 # global options
|
|
|
|
alpine-1 alpine-1 alpine --image-specific-option
|
|
alpine-1:test alpine-1a --another-image-specific-option
|
|
```
|
|
|
|
If the base image is `NONE` (all caps), the target
|
|
image is not checked against its real base image.
|
|
Changes to the base image will then not cause a rebuild.
|
|
|
|
The target image may contain the full name, in which
|
|
case it will contain one or more '/' characters.
|
|
|
|
Another option is to specify only the last part of the
|
|
image name. Then `docker_build` uses the `DOCKER_ACCOUNT`
|
|
environment variable as its initial part. For example, an
|
|
DOCKER_ACCOUNT value of "ghcr.io/b-ehlers" plus the image
|
|
name of "alpine-1" results in "ghcr.io/b-ehlers/alpine-1".
|
|
|
|
This method is not applied to the base images, they always
|
|
have to contain the complete name.
|
|
|
|
But there is a workaround.
|
|
|
|
If the base image name starts with `$DOCKER_ACCOUNT`
|
|
or `${DOCKER_ACCOUNT}` the variable DOCKER_ACCOUNT
|
|
gets replaced by its value from the environment.
|
|
In the Dockerfile the variable must be declared by a
|
|
`ARG DOCKER_ACCOUNT` instruction. A Dockerfile would
|
|
then start with:
|
|
|
|
```
|
|
ARG DOCKER_ACCOUNT
|
|
FROM $DOCKER_ACCOUNT/base-image
|
|
```
|
|
|
|
|
|
## Workflow Definition
|
|
|
|
[GitHub Actions](https://docs.github.com/en/actions)
|
|
uses YAML files in the .github/workflows directory
|
|
to define, which tasks should be run.
|
|
|
|
Before `docker_build` can be run the following steps
|
|
need to be done:
|
|
|
|
* Check out the repository code
|
|
* Set up QEMU (for multi-arch building)
|
|
* Set up Docker Buildx
|
|
* Login to the Container Registry
|
|
* Install python requirements
|
|
|
|
Then `docker_build` can be executed,
|
|
normally without any arguments.
|
|
|
|
But what, when an image build needs to be forced?
|
|
For that, run the action manually and enter the list
|
|
of images, separated by spaces, into the input field.
|