How can I store a binary file in a Kubernetes ConfigMap?

Binary ConfigMaps are now supported since Kubernetes version 1.10.0. From the readme notes:

ConfigMap objects now support binary data via a new binaryData field. When using kubectl create configmap --from-file, files containing non-UTF8 data will be placed in this new field in order to preserve the non-UTF8 data. Note that kubectl's --append-hash feature doesn't take binaryData into account. Use of this feature requires 1.10+ apiserver and kubelets. (#57938, @dims)

See the changelog for more details: https://github.com/kubernetes/kubernetes/blob/master/CHANGELOG/CHANGELOG-1.10.md#apps

What I would do is encode this file in base64 and then the container that uses decoded to be able to use it

According to Jorgan Liggitt in Kubernetes issue "Enable ConfigMaps to store binary files as well as character files.", Kubernetes 1.3.6 cannot store a binary file in a ConfigMap.

GitHub comment 1:

config maps store data as string, not []byte... not sure I'd expect to be able to put arbitrary binary content in them"

GitHub comment 2:

@liggitt Do ConfigMaps not encode binary content as strings?

they do not, they store strings. base64-encoding could be layered on top with application logic if desired

I subsequently demonstrated that ConfigMaps do not support binary files.