Notes from the "Conquering Kubernetes with Emacs" presentation

presentation.org

Conquering Kubernetes with Emacs

Specific Annoying workflow

Listing pods with kubectl get pods, then select a pod name and copy paste it into kubectl logs [pod name]

Why?

• I want to streamline my workflow and stop using the terminal
• learn more about kubernetes
• main kubernetes extension for Emacs out there is greedy for permissions
• assimilate! assimilate! assimilate!

Key takeaways

• making a major mode
• interacting with sub-processes
• providing a modern UX

Listing Pods

Requirements

• get pods from shell command with naive processing
• dump that list in an appropriate major mode
• derive our own major mode

Get pods command

kubectl get pods

First pass at massaging

Only keep pod name and discard first line

kubectl get pods --no-headers=true | awk '{print $1}'

Turn that into a lisp string

Using the shell-command-to-string function

(shell-command-to-string "kubectl get pods --no-headers=true | awk '{print $1}'")

Turn that into a lisp list

Just split at every new line with split-string function

(split-string (shell-command-to-string "kubectl get pods --no-headers=true | awk '{print $1}'") "\n")

Tabulated list mode

There’s already a great major to display columns of data: tabulated-list-mode.

Defining the columns

The column format as a vector of (name width) elements where:

• name is the column name
• width is the column width

  [("Col1" 50) ("Col2" 50)]
      

Defining the rows

The row entries as a list of '(id [values....]) where each element is a row where:

• id can be left nil or be a unique id for the row
• [values...] is a vector of row values

  (list '(nil ["row1" "value1"])
        '(nil ["row2" "value2"])
        '(nil ["row3" "value3"]))
      

Putting it all together

(let ((columns [("Col1" 50) ("Col2" 50)])
      (rows (list '(nil ["row1" "value1"])
                  '(nil ["row2" "value2"])
                  '(nil ["row3" "value3"]))))
  (switch-to-buffer "*temp*")
  (setq tabulated-list-format columns)
  (setq tabulated-list-entries rows)
  (tabulated-list-init-header)
  (tabulated-list-print))

Dump our pod lists into tabulated-list-mode

Set up only one column for pod name.

(let ((columns [("Pod" 100)])
      (rows (mapcar (lambda (x) `(nil [,x]))
                    (split-string (shell-command-to-string "kubectl get pods --no-headers=true | awk '{print $1}'") "\n"))))
  (switch-to-buffer "*temp*")
  (setq tabulated-list-format columns)
  (setq tabulated-list-entries rows)
  (tabulated-list-init-header)
  (tabulated-list-print))

Make a major mode out of it

(define-derived-mode kubernetes-mode tabulated-list-mode "Kubernetes"
  "Kubernetes mode"
  (let ((columns [("Pod" 100)])
        (rows (mapcar (lambda (x) `(nil [,x]))
                      (split-string (shell-command-to-string
                                     "kubectl get pods --no-headers=true | awk '{print $1}'") "\n"))))
    (setq tabulated-list-format columns)
    (setq tabulated-list-entries rows)
    (tabulated-list-init-header)
    (tabulated-list-print)))

(defun kubernetes ()
  (interactive)
  (switch-to-buffer "*kubernetes*")
  (kubernetes-mode))

Testing it out

Can summon with M-x kubernetes or

(kubernetes)

Getting kubectl logs into a buffer

Requirements

• async sub-process creation -> no hanging Emacs
• redirect output to a buffer

Getting logs

kubectl logs redis-64896b74dc-zrw7w

Why won’t the naive way work

Not async and meh performance

Proper way to call a process

Use the call-process function and direct it to a buffer

(let ((buffer "*kubectl-logs*"))
  (call-process "kubectl" nil buffer nil "logs" "redis-64896b74dc-zrw7w")
  (switch-to-buffer buffer))

Proper way to call an async process

Use the start-process function instead which will create a process for you

(let ((process "*kubectl*")
      (buffer "*kubectl-logs*"))
  (start-process process buffer "kubectl" "logs" "-f""redis-64896b74dc-zrw7w")
  (switch-to-buffer buffer))

Putting all that into a function

Let’s use the optional arg

(defun kubernetes-get-logs (&optional arg)
  (interactive "P")
  (let ((process "*kubectl*")
        (buffer "*kubectl-logs*"))
    (if arg
        (start-process process buffer "kubectl" "logs" "-f" "redis-64896b74dc-zrw7w")
      (call-process "kubectl" nil buffer nil "logs" "redis-64896b74dc-zrw7w"))
    (switch-to-buffer buffer)))

Try it with M-x kubernetes-get-logs or C-u M-x kubernetes-get-logs

How to connect that function to our major mode

Our major mode is derived from tabulated-list-mode so we can use the function tabulated-list-get-entry which will give us the entry under the cursor as a vector:

(aref (tabulated-list-get-entry) 0)

Putting everything together

(defun kubernetes-get-logs (&optional arg)
  (interactive "P")
  (let ((process "*kubectl*")
        (buffer "*kubectl-logs*")
        (pod (aref (tabulated-list-get-entry) 0)))
    (if arg
        (start-process process buffer "kubectl" "logs" "-f" pod)
      (call-process "kubectl" nil buffer nil "logs" pod))
    (switch-to-buffer buffer)))

Testing it out

Call kubernetes mode with M-x kubernetes and then look at the logs of pod under cursor with M-x kubernetes-get-logs

Modern UX

Requirements

• a meaningful UI for users to interact with our major modes
• transient (from the magit project) is perfect for wrapping CLI tools

A simple transient

(defun test-function ()
  (interactive)
  (message "Test function"))

(define-transient-command test-transient ()
  "Test Transient Title"
  ["Actions"
   ("a" "Action a" test-function)
   ("s" "Action s" test-function)
   ("d" "Action d" test-function)])

(test-transient)

Transient with switches

We can easily define command line switches in our transient interface.

(defun test-function (&optional args)
  (interactive
   (list (transient-args 'test-transient)))
  (message "args: %s" args))

(define-transient-command test-transient ()
  "Test Transient Title"
  ["Arguments"
   ("-s" "Switch" "--switch")
   ("-a" "Another switch" "--another")]
  ["Actions"
   ("d" "Action d" test-function)])

(test-transient)

Transient with params

A bit more complex than simple switches, params let users enter a value.

(defun test-function (&optional args)
  (interactive
   (list (transient-args 'test-transient)))
  (message "args %s" args))

(define-infix-argument test-transient:--message ()
  :description "Message"
  :class 'transient-option
  :shortarg "-m"
  :argument "--message=")

(define-transient-command test-transient ()
  "Test Transient Title"
  ["Arguments"
   ("-s" "Switch" "--switch")
   ("-a" "Another switch" "--another")
   (test-transient:--message)]
  ["Actions"
   ("d" "Action d" test-function)])

(test-transient)

EDIT

After some feedback, I wanted to share that it is simpler and better here to not define the infix argument separately. Instead, the transient could be defined this way and have the same effect

(define-transient-command test-transient ()
       "Test Transient Title"
       ["Arguments"
        ("-s" "Switch" "--switch")
        ("-a" "Another switch" "--another")
        ("-m" "Message" "--message=")] ;; simpler
       ["Actions"
        ("d" "Action d" test-function)])

Our kubernetes-transient

• can just get logs
• can follow logs with -f
• can specify tail length --tail=100
• can combine these options

(define-infix-argument kubernetes-transient:--tail ()
  :description "Tail"
  :class 'transient-option
  :shortarg "-t"
  :argument "--tail=")

(define-transient-command kubernetes-transient ()
  "Test Transient Title"
  ["Arguments"
   ("-f" "Follow" "-f")
   (kubernetes-transient:--tail)]
  ["Actions"
   ("l" "Log" kubernetes-get-logs)])

(kubernetes-transient)

Updating our kubernetes-get-logs

• read args from transient
• check if -f is in args to do async or not
• pass the args into the process functions

(defun kubernetes-get-logs (&optional args)
  (interactive
   (list (transient-args 'kubernetes-transient)))
  (let ((process "*kubectl*")
        (buffer "*kubectl-logs*")
        (pod (aref (tabulated-list-get-entry) 0)))
    (if (member "-f" args)
        (apply #'start-process process buffer "kubectl" "logs" pod args)
      (apply #'call-process "kubectl" nil buffer nil "logs" pod args))
    (switch-to-buffer buffer)))

Connecting the transient to our mode

Simply define a mode map for kubernetes-mode

(defvar kubernetes-mode-map
  (let ((map (make-sparse-keymap)))
    (define-key map (kbd "l") 'kubernetes-transient)
   map))

Trying it out

(kubernetes)

Conclusion

What could be improved

• nicer method to get pods and other columns
• error handling
• no hard coded values
• customization
• could implement a lot of kubernetes functions, not just logs

Resources

• Gist of these notes
• Full extension for kubernetes
• C-h f start-process for doc on processes
• Transient Manual
• Kubernets cheatsheet

I admittedly have not yet done enough research. ( I plan too. ) But as someone coming from the outside, what's not clear to me about transient is how to handle switches which can be used multiple times ( like the --mount switch on docker, for example ). All the examples I've seen seem to assume a switch is only used once and only has a single value[1]. From my first look at the code, I presume I'll need to make a new class which inherits from transient-argument, and keeps a store of the multiple values and renders those in transient-format-value using the switch and use this object in a non-exiting infix command. I plan on trying to make this work in the next couple of days.

Does this sound off-base? Does anyone have any examples of a use case like this? There are certainly plenty of command line tools which support options being used multiple times. ( the -f option for rsync for example )

[1] The code for transient-format-value on a transient option seems to anticipate possible values, but I haven't yet tracked down how those can turn up.

Note that for being able to execute the kubectl command on a remote machine, e.g. when working via tramp, you can use the replacement functions start-file-process and process-file.

Stumbled on this while looking for some examples on Transient - very informative. Thanks!