What is the difference between dockerService and DockerServer in the kubelet source code - kubernetes

Question

When I read the k8s source code, I found that both dockerService located in pkg/kubelet/dockershim/docker_service.go and DockerServer located in pkg/kubelet/dockershim/remote/docker_server.go seem to implement the interface of the CRI shim server.
But I don't understand the difference between the two, why do I need to distinguish between the two?
k8s version is tag 1.23.1

Answer 1

DockerServer simply creates dockershim grpc server
// DockerServer is the grpc server of dockershim.
type DockerServer struct {
// endpoint is the endpoint to serve on.
endpoint string
// service is the docker service which implements runtime and image services.
service DockerService
// server is the grpc server.
server *grpc.Server
}
...
// Start starts the dockershim grpc server.
func (s *DockerServer) Start() error {
glog.V(2).Infof("Start dockershim grpc server")
l, err := util.CreateListener(s.endpoint)
if err != nil {
return fmt.Errorf("failed to listen on %q: %v", s.endpoint, err)
}
// Create the grpc server and register runtime and image services.
s.server = grpc.NewServer()
runtimeapi.RegisterRuntimeServiceServer(s.server, s.service)
runtimeapi.RegisterImageServiceServer(s.server, s.service)
go func() {
// Use interrupt handler to make sure the server to be stopped properly.
h := interrupt.New(nil, s.Stop)
err := h.Run(func() error { return s.server.Serve(l) })
if err != nil {
glog.Errorf("Failed to serve connections: %v", err)
}
}()
return nil
}
DockerService is the interface implement CRI remote service server
// DockerService is the interface implement CRI remote service server.
type DockerService interface {
runtimeapi.RuntimeServiceServer
runtimeapi.ImageServiceServer
}
// **dockerService uses dockershim service to implement DockerService**.
BTW, are you sure you will use in the future? From the latest (5 days ago) news:
Kubernetes is Moving on From Dockershim: Commitments and Next Steps:
Kubernetes is removing dockershim in the upcoming v1.24 release.
If you use Docker Engine as a container runtime for your Kubernetes cluster, get ready to migrate in 1.24
Full removal is targeted in Kubernetes 1.24, in April 2022.
We'll support Kubernetes version 1.23, which includes dockershim, for another year in the Kubernetes project.