cdebug - experimental container debugger

Mostly for troubleshooting slim & distroless containers that lack a shell and other debugging tools. The technique is based on the ideas from this blog post.

Work in progres...

Demo

The command is very similar to docker exec. You point it to the target container, potentially ask the session to be interactive (-it), and specify the debugging toolkit image (busybox or anything starting from nixery.dev/shell).

Important: The target container isn't recreated and/or restarted. And no extra volumes is needed.

Notice how the debugger's shell actually has the original distroless rootfs as its root directory:

$ docker run -d --rm \
  --name my-distroless gcr.io/distroless/nodejs \
  -e 'setTimeout(() => console.log("Done"), 99999999)'

$ go run main.go exec -it my-distroless
{"status":"Pulling from library/busybox","id":"latest"}
{"status":"Digest: sha256:9810966b5f712084ea05bf28fc8ba2c8fb110baa2531a10e2da52c1efc504698"}
{"status":"Status: Image is up to date for busybox:latest"}
+ rm -rf /proc/1/root/.cdebug
+ ln -s /proc/55/root/bin/ /proc/1/root/.cdebug
+ export 'PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/.cdebug'
+ chroot /proc/1/root sh
/ # ls -lah
total 60K
drwxr-xr-x    1 root     root        4.0K Oct 17 23:49 .
drwxr-xr-x    1 root     root        4.0K Oct 17 23:49 ..
lrwxrwxrwx    1 root     root          18 Oct 17 23:49 .cdebug -> /proc/55/root/bin/
-rwxr-xr-x    1 root     root           0 Oct 17 19:49 .dockerenv
drwxr-xr-x    2 root     root        4.0K Jan  1  1970 bin
drwxr-xr-x    2 root     root        4.0K Jan  1  1970 boot
drwxr-xr-x    5 root     root         340 Oct 17 19:49 dev
drwxr-xr-x    1 root     root        4.0K Oct 17 19:49 etc
drwxr-xr-x    3 nonroot  nonroot     4.0K Jan  1  1970 home
drwxr-xr-x    1 root     root        4.0K Jan  1  1970 lib
drwxr-xr-x    2 root     root        4.0K Jan  1  1970 lib64
drwxr-xr-x    5 root     root        4.0K Jan  1  1970 nodejs
dr-xr-xr-x  191 root     root           0 Oct 17 19:49 proc
drwx------    1 root     root        4.0K Oct 17 19:55 root
drwxr-xr-x    2 root     root        4.0K Jan  1  1970 run
drwxr-xr-x    2 root     root        4.0K Jan  1  1970 sbin
dr-xr-xr-x   13 root     root           0 Oct 17 19:49 sys
drwxrwxrwt    2 root     root        4.0K Jan  1  1970 tmp
drwxr-xr-x    1 root     root        4.0K Jan  1  1970 usr
drwxr-xr-x    1 root     root        4.0K Jan  1  1970 var