Kubernetes with nerdctl

March 12, 2023

Kubernetes in version 1.24 provides a big change by removing dockershim it means that with some exceptions like cri-dockerd you won’t see docker on a Kubernetes node. It’s a disadvantage for me to debug stuff directly on a Kubernetes node with the familiar docker CLI command. Of course, we have something similar but working with containerd it’s called ctr, but to be honest, in some concepts it’s a different beast ie. ctr task exec, but what does it mean task? Fortunately, there is something more familiar to what I know before it’s called nerdctl, it has almost the same ui/ux to docker. Let’s compare all of them with the exec subcommand:

# ctr task exec --help
NAME:
   ctr tasks exec - execute additional processes in an existing container

USAGE:
   ctr tasks exec [command options] [flags] CONTAINER CMD [ARG...]

OPTIONS:
   --cwd value       working directory of the new process
   --tty, -t         allocate a TTY for the container
   --detach, -d      detach from the task after it has started execution
   --exec-id value   exec specific id for the process
   --fifo-dir value  directory used for storing IO FIFOs
   --log-uri value   log uri for custom shim logging
   --user value      user id or name

# docker exec --help

Usage:  docker exec [OPTIONS] CONTAINER COMMAND [ARG...]

Run a command in a running container

Options:
  -d, --detach               Detached mode: run command in the background
      --detach-keys string   Override the key sequence for detaching a container
  -e, --env list             Set environment variables
      --env-file list        Read in a file of environment variables
  -i, --interactive          Keep STDIN open even if not attached
      --privileged           Give extended privileges to the command
  -t, --tty                  Allocate a pseudo-TTY
  -u, --user string          Username or UID (format: <name|uid>[:<group|gid>])
  -w, --workdir string       Working directory inside the container

# nerdctl exec --help
Run a command in a running container

Usage: nerdctl exec [flags] CONTAINER COMMAND [ARG...]

Flags:
  -d, --detach             Detached mode: run command in the background
  -e, --env stringArray    Set environment variables
      --env-file strings   Set environment variables from file
  -h, --help               help for exec
  -i, --interactive        Keep STDIN open even if not attached
      --privileged         Give extended privileges to the command
  -t, --tty                Allocate a pseudo-TTY
  -u, --user string        Username or UID (format: <name|uid>[:<group|gid>])
  -w, --workdir string     Working directory inside the container

See also 'nerdctl --help' for the global flags such as '--namespace', '--snapshotter', and '--cgroup-manager'.

Nice 👍