Charmcraft 4.3 release notes

23 June 2026

Learn about the new features, changes, and fixes introduced in Charmcraft 4.3.

Requirements and compatibility

For development and testing, Charmcraft requires a host with a minimum of 4GB RAM running a Linux distribution compatible with systemd.

All versions of Charmcraft require the following software:

We recommend you install the Charmcraft snap. It comes bundled with all its dependencies.

Non-snap installations of Charmcraft have the following dependencies:

What’s new

Charmcraft 4.3 brings the following new features.

Ubuntu 26.04 LTS support for the reactive plugin

The reactive plugin can now build charms on the Ubuntu 26.04 LTS base. Because the python3-venv package was moved to the universe APT repository on Ubuntu 26.04 LTS, the plugin now adds this repository automatically.

See Change to the Ubuntu 26.04 LTS base for guidance on migrating your charm to Ubuntu 26.04 LTS.

Part naming constraints

Part names are now validated more strictly and cannot contain forward slashes (/) in charms built on the ubuntu@26.04 base or higher.

Valkey support in 12-factor app init templates

The init templates for 12-factor app frameworks (Django, Flask, FastAPI, Express.js, Go, and Spring Boot) now include a commented-out valkey_client relation. If you declare this optional interface in your charm’s requires, Charmcraft automatically injects the necessary dpcharmlibs-interfaces charm Python package.

If the valkey_client relation is declared, you can make use of the following environment variables in your app:

  • VALKEY_HOSTNAME

  • VALKEY_PORT

  • VALKEY_USERNAME

  • VALKEY_PASSWORD

See Extensions for details.

Improved test scaffolding

The charmcraft init command now generates charm project files with improved test scaffolding:

  • Templates now use pytest-jubilant as the test runner for integration tests, replacing the previous custom helpers. The @pytest.mark.juju_setup marker is included in integration test scaffolding for machine and Kubernetes profiles.

  • Integration test templates for machine and Kubernetes profiles have improved comments pointing to the canonical guide on writing integration tests.

COS directory structure validation

When packing a 12-factor app charm, Charmcraft now validates the structure of any custom COS (Canonical Observability Stack) directory. If the directory layout is incorrect, Charmcraft reports an error when packing instead of letting an invalid structure cause errors at runtime.

Documentation improvements

Charmcraft 4.3 includes the following new and updated documentation:

  • How to migrate your charm to Ubuntu 26.04

  • Documentation for the django-secret-key-id configuration option

  • Valkey integration reference, including environment variables and integration metadata

  • Plugin differences noted in the guide on managing charm icons

Fixed bugs and issues

The following issues have been resolved in Charmcraft 4.3:

  • #2600 charmcraft pack -p and -o arguments did not work correctly together

Known issues

The following issues were reported and are scheduled to be fixed in upcoming patch releases.

See individual issue links for any mitigations.

  • #2078 charmcraft clean does not clean all platforms for a charm

  • #1990 Cannot stage packages with Charmcraft

  • #2492 Internal error when uploading a charm outside of a project directory

Contributors

We would like to express a big thank you to all the people who contributed to this release:

@activus-d, @bepri, @canon-cat, @danielvnguyen, @dimaqq, @dwilding, @f-atwi, @jahn-junior, @james-garner-canonical, @javierdelapuente, @lengau, @medubelko, @sabaini, @steinbro, @Thanhphan1147, and @tonyandrewmeyer