Kubernetes only permits RuntimeClass values which are valid lowercase
RFC 1123 labels, which disallows the period character. This prevents
cri-dockerd from being able to support configuring alternative shimv2
runtimes for a pod as shimv2 runtime names must contain at least one
period character. Add support for configuring named shimv2 runtimes in
daemon.json so that runtime names can be aliased to
Kubernetes-compatible names.
Allow options to be set on shimv2 runtimes in daemon.json.
The names of the new daemon runtime config fields have been selected to
correspond with the equivalent field names in cri-containerd's
configuration so that users can more easily follow documentation from
the runtime vendor written for cri-containerd and apply it to
daemon.json.
Signed-off-by: Cory Snider <csnider@mirantis.com>
This centralizes more defaults, to be part of the config struct that's
created, instead of interweaving the defaults with other code in various
places.
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
Contrary to popular belief, the OCI Runtime specification does not
specify the command-line API for runtimes. Looking at containerd's
architecture from the lens of the OCI Runtime spec, the _shim_ is the
OCI Runtime and runC is "just" an implementation detail of the
io.containerd.runc.v2 runtime. When one configures a non-default runtime
in Docker, what they're really doing is instructing Docker to create
containers using the io.containerd.runc.v2 runtime with a configuration
option telling the runtime that the runC binary is at some non-default
path. Consequently, only OCI runtimes which are compatible with the
io.containerd.runc.v2 shim, such as crun, can be used in this manner.
Other OCI runtimes, including kata-containers v2, come with their own
containerd shim and are not compatible with io.containerd.runc.v2.
As Docker has not historically provided a way to select a non-default
runtime which requires its own shim, runtimes such as kata-containers v2
could not be used with Docker.
Allow other containerd shims to be used with Docker; no daemon
configuration required. If the daemon is instructed to create a
container with a runtime name which does not match any of the configured
or stock runtimes, it passes the name along to containerd verbatim. A
user can start a container with the kata-containers runtime, for
example, simply by calling
docker run --runtime io.containerd.kata.v2
Runtime names which containerd would interpret as a path to an arbitrary
binary are disallowed. While handy for development and testing it is not
strictly necessary and would allow anyone with Engine API access to
trivially execute any binary on the host as root, so we have decided it
would be safest for our users if it was not allowed.
It is not yet possible to set an alternative containerd shim as the
default runtime; it can only be configured per-container.
Signed-off-by: Cory Snider <csnider@mirantis.com>
