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.

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
============================================================
  ...

============================================================
Scenario 2: Read-Only PVC (Named Volume) Mount
============================================================
  ...

============================================================
Scenario 3: Cross-Sandbox Sharing via PVC (Named Volume)
============================================================
  ...

============================================================
Scenario 4: SubPath PVC (Named Volume) Mount
============================================================
  ...

============================================================
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

• Sandbox Lifecycle API Spec -- OpenAPI schema for volume definitions
• Host Volume Mount Example -- Host path bind mount example (alternative approach)
• Source code on GitHub