feat: Add ephemeral-docker.sh for running docker in temporary environment

This script creates an isolated temporary docker environment that:
- Starts temporary containerd and dockerd with unique state directories
- Cleans up completely on exit (processes, mounts, files)
- Handles signals and timeouts properly
- Preserves command exit codes

Useful for running docker commands before the system dockerd is started,
e.g., during early boot in init scripts.

Author: kvinwang

basefiles/ephemeral-docker.sh

@@ -0,0 +1,118 @@
+#!/bin/bash
+# ephemeral-docker.sh - Run docker commands in a temporary dockerd environment
+# Usage: ephemeral-docker.sh <docker-command> [args...]
+# Example: ephemeral-docker.sh run --rm hello-world
+#
+# This script creates an isolated temporary docker environment that:
+# - Uses a unique temporary directory for all state
+# - Cleans up completely on exit
+
+set -e
+
+if [ $# -eq 0 ]; then
+    echo "Usage: $0 <docker-command> [args...]" >&2
+    echo "Example: $0 run --rm hello-world" >&2
+    exit 1
+fi
+
+TMPDIR=$(mktemp -d)
+CONTAINERD_PID=""
+DOCKERD_PID=""
+EXIT_CODE=0
+
+cleanup() {
+    local exit_code=$?
+    set +e  # Don't exit on error during cleanup
+
+    # Stop dockerd first (it depends on containerd)
+    if [ -n "$DOCKERD_PID" ] && kill -0 $DOCKERD_PID 2>/dev/null; then
+        kill -TERM $DOCKERD_PID 2>/dev/null
+        # Wait with timeout
+        for i in $(seq 1 50); do
+            kill -0 $DOCKERD_PID 2>/dev/null || break
+            sleep 0.1
+        done
+        # Force kill if still running
+        kill -9 $DOCKERD_PID 2>/dev/null || true
+        wait $DOCKERD_PID 2>/dev/null || true
+    fi
+
+    # Stop containerd
+    if [ -n "$CONTAINERD_PID" ] && kill -0 $CONTAINERD_PID 2>/dev/null; then
+        kill -TERM $CONTAINERD_PID 2>/dev/null
+        for i in $(seq 1 50); do
+            kill -0 $CONTAINERD_PID 2>/dev/null || break
+            sleep 0.1
+        done
+        kill -9 $CONTAINERD_PID 2>/dev/null || true
+        wait $CONTAINERD_PID 2>/dev/null || true
+    fi
+
+    # Unmount any netns that docker created
+    if [ -d "$TMPDIR/docker-exec/netns" ]; then
+        find "$TMPDIR/docker-exec/netns" -type f 2>/dev/null | while read ns; do
+            umount "$ns" 2>/dev/null || true
+        done
+    fi
+
+    # Remove temporary directory
+    rm -rf "$TMPDIR"
+
+    exit ${EXIT_CODE:-$exit_code}
+}
+trap cleanup EXIT INT TERM
+
+# Create all directories
+mkdir -p "$TMPDIR"/{containerd,containerd-state,docker-data,docker-exec}
+
+# Start temporary containerd with isolated state
+containerd \
+    --root "$TMPDIR/containerd" \
+    --state "$TMPDIR/containerd-state" \
+    --address "$TMPDIR/containerd.sock" \
+    &>/dev/null &
+CONTAINERD_PID=$!
+
+# Wait for containerd socket with timeout
+TIMEOUT=100  # 10 seconds
+for i in $(seq 1 $TIMEOUT); do
+    [ -S "$TMPDIR/containerd.sock" ] && break
+    if ! kill -0 $CONTAINERD_PID 2>/dev/null; then
+        echo "Error: containerd exited unexpectedly" >&2
+        exit 1
+    fi
+    sleep 0.1
+done
+if [ ! -S "$TMPDIR/containerd.sock" ]; then
+    echo "Error: Timeout waiting for containerd socket" >&2
+    exit 1
+fi
+
+# Start temporary dockerd with isolated state
+dockerd \
+    --data-root "$TMPDIR/docker-data" \
+    --exec-root "$TMPDIR/docker-exec" \
+    --pidfile "$TMPDIR/docker.pid" \
+    --host "unix://$TMPDIR/docker.sock" \
+    --containerd "$TMPDIR/containerd.sock" \
+    &>/dev/null &
+DOCKERD_PID=$!
+
+# Wait for docker socket with timeout
+for i in $(seq 1 $TIMEOUT); do
+    [ -S "$TMPDIR/docker.sock" ] && break
+    if ! kill -0 $DOCKERD_PID 2>/dev/null; then
+        echo "Error: dockerd exited unexpectedly" >&2
+        exit 1
+    fi
+    sleep 0.1
+done
+if [ ! -S "$TMPDIR/docker.sock" ]; then
+    echo "Error: Timeout waiting for docker socket" >&2
+    exit 1
+fi
+
+# Run the docker command and capture exit code
+docker -H "unix://$TMPDIR/docker.sock" "$@" || EXIT_CODE=$?
+
+# Cleanup happens via trap