Docker PVC (Named Volume) Mount Example

This example demonstrates how to mount Docker named volumes into sandbox containers using the OpenSandbox pvc backend. In Docker runtime, pvc.claimName maps to a Docker named volume -- providing a more convenient and secure alternative to host-path bind mounts for sharing data across sandboxes.

What is pvc? The pvc backend is a runtime-neutral abstraction. In Kubernetes it maps to a PersistentVolumeClaim; in Docker it maps to a named volume. The same API request works on both runtimes. See OSEP-0003 for the design.

Why Named Volumes over Host Paths?

	Host path (host backend)	Named volume (pvc backend)
Security	Exposes host filesystem paths	Docker manages storage location; no host path exposed
Setup	Requires allowed_host_paths allowlist	No allowlist needed
Cross-sandbox sharing	All containers must agree on a host path	Reference the same volume name
Portability	Tied to host directory structure	Works on any Docker host
Lifecycle	User manages host directories	docker volume create/rm

Scenarios

#	Scenario	Description
1	Read-write mount	Mount a named volume for bidirectional file I/O
2	Read-only mount	Mount a named volume that sandboxes cannot modify
3	Cross-sandbox sharing	Two sandboxes share data through the same named volume
4	SubPath mount	Mount only a subdirectory of a named volume (consistent with K8s PVC subPath)

Prerequisites

1. Start OpenSandbox Server

uv pip install opensandbox-server
opensandbox-server init-config ~/.sandbox.toml --example docker
opensandbox-server

2. Create a Docker Named Volume

# Create the named volume
docker volume create opensandbox-pvc-demo

# Seed it with a marker file via a temporary container
docker run --rm -v opensandbox-pvc-demo:/data alpine \
  sh -c "echo 'hello-from-named-volume' > /data/marker.txt"

3. Install Python SDK

uv pip install opensandbox

4. Pull the Sandbox Image

docker pull ubuntu:latest

Run

uv run python examples/docker-pvc-volume-mount/main.py

The script automatically creates the named volume and seeds it with test data. You can also specify a custom volume name or image:

SANDBOX_IMAGE=ubuntu SANDBOX_DOMAIN=localhost:8080 uv run python examples/docker-pvc-volume-mount/main.py

Expected Output

OpenSandbox server : localhost:8080
Sandbox image      : ubuntu
Docker volume      : opensandbox-pvc-demo
  Ensuring Docker named volume 'opensandbox-pvc-demo' exists...
  Created volume 'opensandbox-pvc-demo' with marker.txt

============================================================
Scenario 1: Read-Write PVC (Named Volume) Mount
============================================================
  Volume name: opensandbox-pvc-demo
  Mount path : /mnt/data

  [1] Reading marker file from named volume:
  hello-from-named-volume

  [2] Writing a file from inside the sandbox:
  -> Written: /mnt/data/sandbox-output.txt

  [3] Reading back the written file:
  written-by-sandbox

  [4] Listing volume contents:
  ...
  -rw-r--r-- 1 root root   ... marker.txt
  -rw-r--r-- 1 root root   ... sandbox-output.txt

  Scenario 1 completed.

============================================================
Scenario 2: Read-Only PVC (Named Volume) Mount
============================================================
  Volume name: opensandbox-pvc-demo
  Mount path : /mnt/readonly

  [1] Reading marker.txt from read-only mount:
  hello-from-named-volume

  [2] Attempting to write (should fail):
  touch: cannot touch '/mnt/readonly/should-fail.txt': Read-only file system
  Write denied (expected)

  Scenario 2 completed.

============================================================
Scenario 3: Cross-Sandbox Sharing via PVC (Named Volume)
============================================================
  Volume name: opensandbox-pvc-demo

  [Sandbox A] Creating sandbox and writing data...
  [Sandbox A] Wrote /mnt/shared/cross-sandbox.txt

  [Sandbox B] Creating sandbox and reading data...
  [Sandbox B] Reading file written by Sandbox A:
  message-from-sandbox-a

  Cross-sandbox data sharing verified!

  Scenario 3 completed.

============================================================
Scenario 4: SubPath PVC (Named Volume) Mount
============================================================
  Volume name: opensandbox-pvc-demo
  SubPath    : datasets/train
  Mount path : /mnt/training-data

  [1] Listing mounted subpath content:
  ...
  -rw-r--r-- 1 root root   ... data.csv

  [2] Reading data.csv:
  id,value
  1,100
  2,200

  [3] Verifying volume root is NOT visible:
  marker.txt at mount root: NOT-FOUND
  -> Confirmed: subPath isolation is working correctly

  Scenario 4 completed.

============================================================
All scenarios completed successfully!
============================================================

SDK Usage Quick Reference

Python (async)

from opensandbox import Sandbox
from opensandbox.models.sandboxes import PVC, Volume

sandbox = await Sandbox.create(
    image="ubuntu",
    volumes=[
        Volume(
            name="my-data",
            pvc=PVC(claimName="my-named-volume"),
            mountPath="/mnt/data",
            readOnly=False,       # optional, default is False
            subPath="datasets/train",  # optional, mount a subdirectory
        ),
    ],
)

Python (sync)

from opensandbox import SandboxSync
from opensandbox.models.sandboxes import PVC, Volume

sandbox = SandboxSync.create(
    image="ubuntu",
    volumes=[
        Volume(
            name="my-data",
            pvc=PVC(claimName="my-named-volume"),
            mountPath="/mnt/data",
            subPath="datasets/train",  # optional
        ),
    ],
)

JavaScript / TypeScript

import { Sandbox } from "@alibaba-group/opensandbox";

const sandbox = await Sandbox.create({
  image: "ubuntu",
  volumes: [
    {
      name: "my-data",
      pvc: { claimName: "my-named-volume" },
      mountPath: "/mnt/data",
      readOnly: false,
      subPath: "datasets/train",  // optional
    },
  ],
});

Java / Kotlin

Volume volume = Volume.builder()
    .name("my-data")
    .pvc(PVC.of("my-named-volume"))
    .mountPath("/mnt/data")
    .readOnly(false)
    .subPath("datasets/train")  // optional
    .build();

Sandbox sandbox = Sandbox.builder()
    .image("ubuntu")
    .volume(volume)
    .build();

Cleanup

docker volume rm opensandbox-pvc-demo

References

• OSEP-0003: Volume and VolumeBinding Support -- Design proposal
• Sandbox Lifecycle API Spec -- OpenAPI schema for volume definitions
• Host Volume Mount Example -- Host path bind mount example (alternative approach)

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This page is sourced from: examples/docker-pvc-volume-mount/README.md