chore: update dind examples to use onCreateCommand (#350)

Author: johnstcn

docs/docker.md

@@ -9,7 +9,8 @@ from inside Envbuilder.
 > you may need to instead add the relevant content of the init script to your
 > agent startup script in your template.
 > For example:
-> ```
+>
+> ```terraform
 >   resource "coder_agent" "dev" {
 >     ...
 >     startup_script = <<-EOT
@@ -43,7 +44,6 @@ docker run -it --rm \
     ghcr.io/coder/envbuilder:latest
 ```
 
-
 ## Docker-in-Docker (DinD)
 
 **Security:** Low
@@ -57,16 +57,16 @@ Example:
 
 > Note that due to a lack of init system, the Docker daemon
 > needs to be started separately inside the container. In this example, we
-> create a custom entrypoint to start the Docker daemon in the background and
-> call this entrypoint via `ENVBUILDER_INIT_SCRIPT`.
+> create a custom script to start the Docker daemon in the background and
+> call this entrypoint via the Devcontainer `onCreateCommand` lifecycle hook.
 
 ```console
 docker run -it --rm \
     --privileged \
     -v /tmp/envbuilder:/workspaces \
     -e ENVBUILDER_GIT_URL=https://github.com/coder/envbuilder \
     -e ENVBUILDER_DEVCONTAINER_DIR=/workspaces/envbuilder/examples/docker/02_dind \
-    -e ENVBUILDER_INIT_SCRIPT=/entrypoint.sh \
+    -e ENVBUILDER_INIT_SCRIPT=bash \
     ghcr.io/coder/envbuilder:latest
 ```
 
@@ -75,8 +75,14 @@ docker run -it --rm \
 The above can also be accomplished using the [`docker-in-docker` Devcontainer
 feature](https://github.com/devcontainers/features/tree/main/src/docker-in-docker).
 
-> Note: we still need the custom entrypoint to start the docker startup script.
-> See https://github.com/devcontainers/features/blob/main/src/docker-in-docker/devcontainer-feature.json#L60
+> Note: we still need the `onCreateCommand` to start Docker.
+> See
+> [here](https://github.com/devcontainers/features/blob/main/src/docker-in-docker/devcontainer-feature.json#L65)
+> for more details.
+>
+> Known issue: `/run` does not get symlinked correctly to `/var/run`.
+> To work around this, we create the symlink manually before running
+> the script to start the Docker daemon.
 
 Example:
 
@@ -86,7 +92,7 @@ docker run -it --rm \
     -v /tmp/envbuilder:/workspaces \
     -e ENVBUILDER_GIT_URL=https://github.com/coder/envbuilder \
     -e ENVBUILDER_DEVCONTAINER_DIR=/workspaces/envbuilder/examples/docker/03_dind_feature \
-    -e ENVBUILDER_INIT_SCRIPT=/entrypoint.sh \
+    -e ENVBUILDER_INIT_SCRIPT=bash \
     ghcr.io/coder/envbuilder:latest
 ```
 
@@ -95,7 +101,7 @@ docker run -it --rm \
 **Security:** Medium
 **Convenience:** Medium
 
-This approach runs a Docker daemon in *rootless* mode.
+This approach runs a Docker daemon in _rootless_ mode.
 While this still requires a privileged container, this allows you to restrict
 usage of the `root` user inside the container, as the Docker daemon will be run
 under a "fake" root user (via `rootlesskit`). The user inside the workspace can
@@ -129,6 +135,7 @@ including transparently enabling Docker inside workspaces. Most notably, it
 access inside their workspaces, if required.
 
 Example:
+
 ```console
 docker run -it --rm \
     -v /tmp/envbuilder:/workspaces \

examples/docker/02_dind/Dockerfile

@@ -1,6 +1,23 @@
 FROM ubuntu:noble
+
+# Install Docker using Docker's convenience script.
 RUN apt-get update && \
-  apt-get install -y curl apt-transport-https && \
-  curl -fsSL https://get.docker.com/ | sh -s -
-ADD entrypoint.sh /entrypoint.sh
-ENTRYPOINT ["/entrypoint.sh"]
+    apt-get install -y curl sudo apt-transport-https && \
+    curl -fsSL https://get.docker.com/ | sh -s -
+
+# The ubuntu:noble image includes a non-root user by default,
+# but it does not have sudo privileges. We need to set this up.
+# Note: we chown /var/run/docker.sock to the non-root user
+# in the onCreateCommand script. Ideally you would add the
+# non-root user to the docker group, but in this scenario
+# this is a 'single-user' environment. It also avoids us
+# having to run `newgrp docker`.
+RUN echo "ubuntu ALL=(ALL) NOPASSWD:ALL" > /etc/sudoers.d/ubuntu
+
+# Add our onCreateCommand script.
+ADD on-create.sh /on-create.sh
+
+# Switch to the non-root user.
+USER ubuntu
+
+ENTRYPOINT ["bash"]

examples/docker/02_dind/devcontainer.json

@@ -1,5 +1,6 @@
 {
   "build": {
     "dockerfile": "Dockerfile"
-  }
-}
+  },
+  "onCreateCommand": "/on-create.sh"
+}

examples/docker/02_dind/entrypoint.sh

@@ -0,0 +1,22 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+# Start Docker in the background.
+sudo -u root /bin/sh -c 'nohup dockerd > /var/log/docker.log &'
+
+# Wait up to 10 seconds for Docker to start.
+for attempt in $(seq 1 10); do
+  if [[ $attempt -eq 10 ]]; then
+    echo "Failed to start Docker"
+    exit 1
+  fi
+  if [[ ! -e /var/run/docker.sock ]]; then
+    sleep 1
+  else
+    break
+  fi
+done
+
+# Change the owner of the Docker socket so that the non-root user can use it.
+sudo chown ubuntu:docker /var/run/docker.sock

examples/docker/02_dind/on-create.sh

@@ -1,3 +1,22 @@
 FROM ubuntu:noble
-ADD entrypoint.sh /entrypoint.sh
-ENTRYPOINT ["/entrypoint.sh"]
+
+# Install some dependencies such as curl and sudo.
+# Also set up passwordless sudo for the ubuntu user.
+RUN apt-get update && \
+    DEBIAN_FRONTEND=noninteractive apt-get install -y \
+      curl \
+      sudo \
+      apt-transport-https && \
+    echo "ubuntu ALL=(ALL) NOPASSWD:ALL" > /etc/sudoers.d/ubuntu
+
+# Add our onCreateCommand script.
+ADD on-create.sh /on-create.sh
+
+# Switch to the non-root user.
+USER ubuntu
+
+# The devcontainer feature provides /usr/local/share/docker-init.sh
+# which will handle most of the steps of setting up Docker.
+# We can't put this in the entrypoint as it gets overridden, so
+# we call it in the on-create script.
+ENTRYPOINT ["bash"]

examples/docker/03_dind_feature/Dockerfile

@@ -2,7 +2,8 @@
   "build": {
     "dockerfile": "Dockerfile"
   },
+  "onCreateCommand": "/on-create.sh",
   "features": {
     "ghcr.io/devcontainers/features/docker-in-docker:2": {}
   }
-}
+}

examples/docker/03_dind_feature/devcontainer.json

@@ -0,0 +1,18 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+# Known issue: Kaniko does not symlink /run => /var/run properly.
+# This results in /var/run/ being owned by root:root which interferes
+# with accessing the Docker socket even if the permissions are set
+# correctly. Workaround: symlink it manually
+sudo ln -s /run /var/run
+
+# Run the docker init script. This needs to be
+# run as root. It will take care of starting the
+# daemon and adding the ubuntu user to the docker
+# group.
+sudo /usr/local/share/docker-init.sh
+
+# Change the owner of the Docker socket so that the non-root user can use it.
+sudo chown ubuntu:docker /var/run/docker.sock

examples/docker/03_dind_feature/entrypoint.sh

@@ -1,8 +1,11 @@
 FROM ubuntu:noble
+
 # Based on UID of ubuntu user in container.
 ENV XDG_RUNTIME_DIR /run/user/1000
 ENV DOCKER_HOST unix:///${XDG_RUNTIME_DIR}/docker.sock
+
 # Setup as root
+USER root
 RUN apt-get update && \
   # Install prerequisites
   apt-get install -y apt-transport-https curl iproute2 uidmap && \
@@ -19,6 +22,8 @@ USER ubuntu
 RUN dockerd-rootless-setuptool.sh install && \
   docker context use rootless && \
   mkdir -p /home/ubuntu/.local/share/docker
-# Add our custom entrypoint
-ADD entrypoint.sh /entrypoint.sh
-ENTRYPOINT ["/entrypoint.sh"]
+
+# Add our onCreateCommand script.
+ADD on-create.sh /on-create.sh
+
+ENTRYPOINT ["bash"]

examples/docker/03_dind_feature/on-create.sh

@@ -1,5 +1,6 @@
 {
   "build": {
     "dockerfile": "Dockerfile"
-  }
-}
+  },
+  "onCreateCommand": "/on-create.sh"
+}

examples/docker/04_dind_rootless/Dockerfile

@@ -3,6 +3,4 @@
 set -euo pipefail
 
 # Start the rootless docker daemon as a non-root user
-nohup rootlesskit --net=slirp4netns --mtu=1500 --disable-host-loopback --port-driver=builtin --copy-up=/etc --copy-up=/run dockerd > "/tmp/dockerd-rootless.log" 2>&1 &
-
-exec bash --login
+nohup rootlesskit --net=slirp4netns --mtu=1500 --disable-host-loopback --port-driver=builtin --copy-up=/etc --copy-up=/run dockerd >"/tmp/dockerd-rootless.log" 2>&1 &