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https://github.com/iximiuz/cdebug

cdebug - a swiss army knife of container debugging
https://github.com/iximiuz/cdebug

containerd containers debug distroless docker kubernetes

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cdebug - a swiss army knife of container debugging

Host: GitHub
URL: https://github.com/iximiuz/cdebug
Owner: iximiuz
License: apache-2.0
Created: 2022-10-22T15:22:44.000Z (about 2 years ago)
Default Branch: main
Last Pushed: 2024-04-13T13:58:35.000Z (7 months ago)
Last Synced: 2024-04-14T04:12:05.767Z (7 months ago)
Topics: containerd, containers, debug, distroless, docker, kubernetes
Language: Go
Homepage: https://iximiuz.com/en/posts/docker-debug-slim-containers/
Size: 521 KB
Stars: 1,075
Watchers: 17
Forks: 38
Open Issues: 7
Metadata Files:
- Readme: README.md
- License: LICENSE

Awesome Lists containing this project

README

# cdebug - a swiss army knife of container debugging

```diff
! Support development of this project > patreon.com/iximiuz
```

With this tool you can:

- Troubleshoot containers and pods lacking shell and/or debugging tools.
- Forward unpublished or even localhost ports to your host system.
- Expose endpoints from the host system to containers & Kubernetes networks.
- Handily export image's and/or container's filesystem to local folders.
- and more :)

The following _commands_ x _runtimes_ are supported:

| | Docker | Podman | containerd | OCI (runc, crun) | Kubernetes | CRI |
| :--- | :---: | :---: | :---: | :---: | :---: | :---: |
| `exec` | ✅ | - | ✅ | - | ✅ | - |
| `port-forward` local | ✅ | - | - | - | - | - |
| `port-forward` remote | 🛠️ | - | - | - | - | - |
| `export` | - | - | - | - | - | - |

## Installation

It's a statically linked Go binary, so you know the drill:

```sh
GOOS=linux
GOARCH=amd64

curl -Ls https://github.com/iximiuz/cdebug/releases/latest/download/cdebug_${GOOS}_${GOARCH}.tar.gz | tar xvz

sudo mv cdebug /usr/local/bin
```

### Homebrew

If you're a [Homebrew](https://brew.sh/) user, you can install the tool via brew on macOS or Linux:

```sh
$ brew install cdebug
```

At the moment, the following systems are (kinda sorta) supported:

- linux/amd64
- darwin/amd64
- darwin/arm64

## Commands

### cdebug exec

Execute commands or start interactive shells in scratch, slim, or distroless containers, with ease:

```sh
# Start a busybox:musl shell in the Docker container:
cdebug exec -it mycontainer
cdebug exec -it docker://mycontainer

# Execute a command in the Docker container:
cdebug exec mycontainer cat /etc/os-release

# Use a different debugging toolkit image:
cdebug exec -it --image=alpine mycontainer

# Use a nixery.dev image (https://nixery.dev/):
cdebug exec -it --image=nixery.dev/shell/vim/ps/tshark mycontainer

# Exec into a containerd container:
cdebug exec -it containerd://mycontainer ...
cdebug exec --namespace myns -it containerd://mycontainer ...

# Exec into a nerdctl container:
cdebug exec -it nerdctl://mycontainer ...

# Start a shell in a Kubernetes pod:
cdebug exec -it pod/mypod
cdebug exec -it k8s://mypod
cdebug exec --namespace=myns -it pod/mypod

# Start a shell in a Kubernetes pod's container:
cdebug exec -it pod/mypod/mycontainer
```

The `cdebug exec` command is a crossbreeding of `docker exec` and `kubectl debug` commands.
You point the tool at a running container, say what toolkit image to use, and it starts
a debugging "sidecar" container that _feels_ like a `docker exec` session to the target container:

- The root filesystem of the debugger **_is_** the root filesystem of the target container.
- The target container isn't recreated and/or restarted.
- No extra volumes or copying of debugging tools is needed.
- The debugging tools **_are_** available in the target container.

By default, the `busybox:musl` (statically compiled) image is used for the debugger sidecar, but you can override it
with the `--image` flag. Combining this with the superpower of Nix and [Nixery](https://nixery.dev/),
you can get all your favorite tools by simply listing them in the image name:

```
cdebug exec -it --image nixery.dev/shell/ps/vim/tshark
```

How it works

The technique is based on the ideas from this [blog post](https://iximiuz.com/en/posts/docker-debug-slim-containers).

![How: cdebug exec](assets/images/cdebug-exec.png)

Oversimplifying, the debugger container is started like:

```sh
docker run [-it] \
--network container: \
--pid container: \
--uts container: \

sh -c <

### cdebug port-forward

Forward local ports to containers and vice versa. This command is another crossbreeding -
this time it's `kubectl port-forward` and `ssh -L|-R`.

Currently, only local port forwarding (`cdebug port-forward -L`) is supported,
but remote port forwarding is under active development.

Local port forwarding use cases (works for Docker Desktop too!):

- Publish "unpublished" port 80 to a random port on the host: `cdebug port-forward -L 80`
- Expose container's localhost to the host system: `cdebug port-forward -L 127.0.0.1:5432`
- Proxy local traffic to a remote host via the target: `cdebug port-forward -L :::`
- 🛠️ Expose a Kubernetes service to the host system: `cdebug port-forward -L 8888:my.svc.cluster.local:443`

Remote port forwarding use cases:

- Start a container/Pod forwarding traffic destined to its `:` to a non-cluster endpoint reachable from the host system.
- ...

How it works

**Local port forwarding** is implemented by starting an extra forwarder container in the
target's network and publishing its ports to the host using the standard means (e.g.,
`docker run --publish`). The forwarder container itself runs something like:

`socat TCP-LISTEN:,fork TCP-CONNECT::`

![How: cdebug port-forward -L (direct)](assets/images/cdebug-port-forward-local-direct.png)

If the _REMOTE_HOST_ doesn't belong to the target or it's the target's localhost,
an extra sidecar container is started in the target's network namespace with another
socat forwarding traffic from the target public interface to `REMOTE_HOST:REMOTE_PORT`.

![How: cdebug port-forward -L (sidecar)](assets/images/cdebug-port-forward-local-sidecar.png)

**Remote port forwarding** will use similar tricks but combined with more advanced
reverse tunneling.

## Examples

Below are a few popular scenarios formatted as reproducible demos.

### A simple interactive shell to a distroless container

First, a target container is needed. Let's use a distroless nodejs image for that:

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

Now, let's start an interactive shell (using busybox) into the above container:

```sh
$ cdebug exec -it my-distroless
```

Exploring the filesystem shows that it's a rootfs of the nodejs container:

```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-c153d669 -> /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
...
```

Notice 👉 above - that's where the debugging tools live:

```sh
/ $# echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/.cdebug-c153d669
```

The process tree of the debugger container is the process tree of the target:

```sh
/ $# ps auxf
PID USER TIME COMMAND
1 root 0:00 /nodejs/bin/node -e setTimeout(() => console.log("Done"),
13 root 0:00 sh -c set -euo pipefail sleep 999999999 & SANDBOX_PID=$!
19 root 0:00 sleep 999999999
21 root 0:00 sh
28 root 0:00 [sleep]
39 root 0:00 [sleep]
45 root 0:00 ps auxf
```

### An interactive shell with code editor (vim)

If the tools provided by busybox aren't enough, you can bring your own tools with
a ~~little~~ huge help of the [nixery](https://nixery.dev/) project:

```sh
$ cdebug exec -it --image nixery.dev/shell/vim my-distroless
```

### An interactive shell with tshark and other advanced tools

Even more powerful exammple:

```sh
$ cdebug exec -it --image nixery.dev/shell/ps/findutils/tshark my-distroless
```

### Debugging containerd containers (no Docker required)

First, start the target container:

```sh
$ sudo ctr image pull docker.io/library/nginx:latest
$ sudo ctr run -d docker.io/library/nginx:latest nginx-1
```

Run an interactive shell in the target container using simple `cdebug exec`:

```
$ sudo cdebug exec -it containerd://nginx-1
/ $# wget -O- 127.0.0.1
```

Run VIM in the target container using `cdebug exec --image nixery.dev/shell/vim`:

```sh
$ sudo cdebug exec -it --rm --image nixery.dev/shell/vim containerd://nginx-1
```

### Debugging nerdctl containers (no Docker required)

Start a container using nerdctl:

```sh
$ sudo $(which nerdctl) run -d --name nginx-1 nginx
9f8763d82259a6e3e747df83d0ce8b7ee3d33d94269a72cd04e0e3862a3abc5f
```

Run the debugger using the `nerdctl://` schema and the target's name:

```sh
$ sudo cdebug exec -it --rm nerdctl://nginx-1
```

Or run a debugging session in the above container using the `containerd://` schema:

```sh
$ sudo cdebug exec -it --rm containerd://9f876
```

### Debugging Kubernetes Pods (without node access)

Start the target Pod:

```sh
$ kubectl run --image nginx:alpine nginx-1
$ kubectl run --image=nginx:alpine nginx-1 \
--overrides='{ "apiVersion": "v1", "spec": { "containers": [{ "name": "app", "image": "nginx:alpine" }] } }'
pod/nginx-1 created

$ kubectl get pods
NAME READY STATUS RESTARTS AGE
nginx-1 1/1 Running 0 5s
```

Run the debugger in the Pod (it'll start a new ephemeral container):

```sh
$ cdebug exec -it pod/nginx-1
```

Expected output:

```text
Debugger container name: cdebug-3023d11d
Starting debugger container...
Waiting for debugger container...
Attaching to debugger container...
If you don't see a command prompt, try pressing enter.
/ # ps auxf
PID USER TIME COMMAND
1 root 0:00 sh /.cdebug-entrypoint.sh
10 root 0:00 /bin/sh -i
11 root 0:00 ps auxf
```

Run the debugger in the Nginx container (`app`):

```sh
$ cdebug exec -it pod/nginx-1/app
```

```text
cdebug exec -it pod/nginx-1/app
Debugger container name: cdebug-b44ca485
Starting debugger container...
Waiting for debugger container...
Attaching to debugger container...
If you don't see a command prompt, try pressing enter.
/ # ps auxf
PID USER TIME COMMAND
1 root 0:00 nginx: master process nginx -g daemon off;
30 nginx 0:00 nginx: worker process
...
41 nginx 0:00 nginx: worker process
42 root 0:00 sh /.cdebug-entrypoint.sh
51 root 0:00 /bin/ash -i
52 root 0:00 ps auxf
```

### Debugging Kubernetes Pods (with node access)

Currently, only containerd CRI is supported. First, you'll need to list the running
containers:

```sh
$ ctr -n k8s.io container ls
CONTAINER IMAGE RUNTIME
155227c0e9aa8 k8s.gcr.io/pause:3.5 io.containerd.runc.v2
2220eacd9cb26 registry.k8s.io/kube-apiserver:v1.25.3 io.containerd.runc.v2
22efcb35a651a registry.k8s.io/etcd:3.5.4-0 io.containerd.runc.v2
28e06cc63b822 docker.io/calico/cni:v3.24.1 io.containerd.runc.v2
30754c8492f18 docker.io/calico/node:v3.24.1 io.containerd.runc.v2
61acdb0231516 docker.io/calico/kube-controllers:v3.24.1 io.containerd.runc.v2
...
```

Now you can exec into a Pod's container bringing your own debugging tools:

```sh
$ cdebug exec -n k8s.io -it --rm containerd://2220ea
```

### Publish "forgotten" port

Start an nginx container but don't expose its port 80:

```sh
$ docker run -d --name nginx-1 nginx:1.23
```

Forward local port 8080 to the nginx's 80:

```sh
$ cdebug port-forward nginx-1 -L 8080:80
$ curl localhost:8080
```

### Expose localhost's ports

Start a containerized service that listens only on its localhost:

```sh
$ docker run -d --name svc-1 python:3-alpine python3 -m 'http.server' -b 127.0.0.1 8888
```

Tap into the above service:

```sh
$ cdebug port-forward svc-1 -L 127.0.0.1:8888
Pulling forwarder image...
latest: Pulling from shell/socat
Digest: sha256:b43b6cf8d22615616b13c744b8ff525f5f6c0ca6c11b37fa3832a951ebb3c20c
Status: Image is up to date for nixery.dev/shell/socat:latest
Forwarding 127.0.0.1:49176 to 127.0.0.1:8888 through 172.17.0.4:34128

$ curl localhost:49176

...
```

## F.A.Q

**Q:** `cdebug exec` fails with `ln: /proc/1/root/...: Permission denied` or the like error?

Non-privileged targets can cause this error because by default, `cdebug` tries to start the debugger container with the same privileges as the target container. Try `cdebug exec --privileged` instead.

## Similar tools

- [`slim debug`](https://github.com/slimtoolkit/slim) - a `debug` command for Slim(toolkit) (originally contributed by [D4N](https://github.com/D4N))
- [`debug-ctr`](https://github.com/felipecruz91/debug-ctr) - a debugger that creates a new container out of the original container with the toolkit mounted in a volume (by [Felipe Cruz Martinez](https://github.com/felipecruz91))
- [`docker-debug`](https://github.com/zeromake/docker-debug) - much like `cdebug exec` but without the chroot trick.
- [`docker-opener`](https://github.com/artemkaxboy/docker-opener) - a multi-purpose tool that in particular can run a shell session into your container (and if there is no shell inside, it'll bring its own busybox).
- [`cntr`](https://github.com/Mic92/cntr) - is "a replacement for `docker exec` that brings all your developers tools with you" by mounting the file system from one container (or the host) into the target container and creating a nested container with the help of a FUSE filesystem. Supports a huge range of runtimes (docker, podman, LXC/LXD, rkt, systemd-nspawn, containerd) because it operates on the OS level.
- [`kdiag`](https://github.com/solo-io/kdiag) - a kubectl plugin to get shell access to scratch containers, stream logs from multiple pods simultaneously, and do reverse port forwarding to Kubernetes clusters.

- [`kpexec`](https://github.com/ssup2/kpexec) - a CLI that runs commands in a Kubernetes container with high privileges (via a privileged Pod with Node access).

## TODO:

- More `exec` flags (like in `docker run`): `--cap-add`, `--cap-drop`, `--env`, `--volume`, etc.
- Helper command(s) suggesting nix(ery) packages
- Non-docker runtimes (Podman, CRI, OCI)
- More E2E Tests

## Contributions

It's a pre-alpha with no sound design yet, so I may not be accepting all PRs. Sorry about that :)