Validate the Kamal configuration giving useful warning on errors.
Each section of the configuration has its own config class and a YAML
file containing documented example configuration.
You can run `kamal docs` to see the example configuration, and
`kamal docs <section>` to see the example configuration for a specific
section.
The validation matches the configuration to the example configuration
checking that there are no unknown keys and that the values are of
matching types.
Where there is more complex validation - e.g for envs and servers, we
have custom validators that implement those rules.
Additonally the configuration examples are used to generate the
configuration documentation in the kamal-site repo.
You generate them by running:
```
bundle exec bin/docs <kamal-site-checkout>
```
Docker does not respect the .dockerignore file when building from a tar.
Instead by default we'll make a local clone into a tmp directory and
build from there. Subsequent builds will reset the clone to match the
checkout.
Compared to building directly in the repo, we'll have reproducible
builds.
Compared to using a git archive:
1. .dockerignore is respected
2. We'll have faster builds - docker can be smarter about caching the
build context on subsequent builds from a directory
To build from the repo directly, set the build context to "." in the
config.
If there are uncommitted changes, we'll warn about them either being
included or ignored depending on whether we build from the clone.
If no context is specified and we are in a git repo, then we'll build
from a git archive by default. This means we don't need a separate
setting and gives us a safer default build.
Building directly from a checkout will pull in uncommitted files to or
more sneakily files that are git ignored, but not docker ignored.
To avoid this, we'll add an option to build from a git archive of HEAD
instead. Docker doesn't provide a way to build directly from a git
repo, so instead we create a tarball of the current HEAD with git
archive and pipe it into the build command.
When building from a git archive, we'll still display the warning about
uncommitted changes, but we won't add the `_uncommitted_...` suffix to
the container name as they won't be included in the build.
Perhaps this should be the default, but we'll leave that decision for
now.
