Secrets (e.g. container pull secrets)

To have bootc fetch updates from registry which requires authentication, you must include a pull secret in /etc/ostree/auth.json (or as of recent versions in /usr/lib/ostree/auth.json).

Another common case is to also fetch container images via podman or equivalent. There is a pull request to add /etc/containers/auth.json which would be shared by the two stacks by default.

Regardless, injecting this data is a good example of a generic "secret". The bootc project does not currently include one single opinionated mechanism for secrets.

Using a credential helper

In order to use a credential helper as configured in registries.conf such as credential-helpers = ["ecr-login"], you must currently also write a "no-op" authentication file with the contents {} (i.e. an empty JSON object, not an empty file) into the pull secret location.

Embedding in container build

This was mentioned above; you can include secrets in the container image if the registry server is suitably protected.

In some cases, embedding only "bootstrap" secrets into the container image is a viable pattern, especially alongside a mechanism for having a machine authenticate to a cluster. In this pattern, a provisioning tool (whether run as part of the host system or a container image) uses the bootstrap secret to lay down and keep updated other secrets (for example, SSH keys, certificates).

Via cloud metadata

Most production IaaS systems support a "metadata server" or equivalent which can securely host secrets - particularly "bootstrap secrets". Your container image can include tooling such as cloud-init or ignition which fetches these secrets.

Embedded in disk images

Another pattern is to embed bootstrap secrets only in disk images. For example, when generating a cloud disk image (AMI, OpenStack glance image, etc.) from an input container image, the disk image can contain secrets that are effectively machine-local state. Rotating them would require an additional management tool, or refreshing disk images.

Injected via baremetal installers

It is common for installer tools to support injecting configuration which can commonly cover secrets like this.

Injecting secrets via systemd credentials

The systemd project has documentation for credentials which applies in some deployment methodologies.