I have a cluster on GKE currently on version v1.19.9-gke.1400. Accordingly do kubernetes release notes, on 1.20 dockershim will be deprecated. My cluster is configured to auto-upgrades and in one specific application I use docker socket mapped to the application, where I run direct containers through their API.
My question: In a hypothetical upgrade of the cluster to the 1.20 version of kubernetes, the docker socket will be unavailable immediately? Or the deprecated flag only points that in the future it will be removed?
Yes, if you use the non-containerd images. In the node pool config you can choose which image type you want and COS vs COS_Containerd are separate choices there. At some point later in 2021 we may (if all goes according to plan) remove Docker support in Kubernetes itself for 1.23. However Google may choose to remove support one version earlier in 1.22 or continue it later via the out-of-tree Docker CRI that Mirantis is working on.
I am running 1.20 in the Rapid channel and can confirm that Docker is still there and happy. Also FWIW if you need to run dockerd yourself via a DaemonSet it takes like 30 seconds to set up, really not a huge deal either way.