Honor Unix DOCKER_HOST sockets for DinD mounts on ARC runners by Copilot · Pull Request #2841 · github/gh-aw-firewall

Copilot · 2026-05-10T14:04:39Z

Bug Fix

What was the bug?

ARC DinD runners can expose Docker through a shared Unix socket without using the default hardcoded path. AWF was still assuming /var/run/docker.sock for DinD socket exposure, so MCP gateway startup could fail even when DOCKER_HOST already pointed at a valid Unix socket.

How did you fix it?

Socket path resolution
- Resolve the DinD socket mount from awfDockerHost first, then DOCKER_HOST, when either uses a unix:// URI.
- Fall back to /var/run/docker.sock only when no valid Unix socket is configured.
- Keep /run/docker.sock mounted only for the standard default socket case.
Agent Docker client alignment
- When --enable-dind is used with --docker-host unix:///path/to/docker.sock, set the agent container's DOCKER_HOST to that same Unix socket so in-agent docker commands target the mounted socket by default.
- This covers the common case where the host process does not already have DOCKER_HOST set, avoiding a mismatch between the mounted DinD socket and the agent's Docker client default.
Invalid config handling
- Warn and fall back cleanly when DOCKER_HOST contains a malformed Unix socket URI.
- Ignore non-Unix DOCKER_HOST values for DinD socket mounting instead of treating them as bind-mount paths.
Coverage and docs
- Add focused tests for custom Unix socket detection, override precedence, malformed Unix socket fallback, and the --docker-host + --enable-dind case when host DOCKER_HOST is unset.
- Document that --docker-host also controls the DinD socket exposed to the agent when --enable-dind is enabled, and that AWF sets the agent's DOCKER_HOST to match.

const dockerHost = config.awfDockerHost ?? process.env.DOCKER_HOST;

if (dockerHost?.startsWith('unix://')) {
  const socketPath = dockerHost.slice('unix://'.length);
  // mount the configured Unix socket into the agent chroot
}

if (config.enableDind && config.awfDockerHost?.startsWith('unix://')) {
  environment.DOCKER_HOST = config.awfDockerHost;
}

github-actions · 2026-05-10T15:24:47Z

Documentation Preview

Documentation build failed for this PR. View logs.

Built from commit b8a97af

github-actions · 2026-05-10T15:25:15Z

✅ Coverage Check Passed

Overall Coverage

Metric	Base	PR	Delta
Lines	87.37%	87.45%	📈 +0.08%
Statements	87.34%	87.41%	📈 +0.07%
Functions	82.70%	82.74%	📈 +0.04%
Branches	79.43%	79.58%	📈 +0.15%

📁 Per-file Coverage Changes (3 files)

File	Lines (Before → After)	Statements (Before → After)
`src/services/agent-volumes.ts`	91.6% → 90.8% (-0.75%)	91.8% → 91.0% (-0.76%)
`src/services/agent-environment.ts`	98.5% → 98.6% (+0.02%)	97.8% → 97.9% (+0.03%)
`src/container-lifecycle.ts`	87.1% → 88.2% (+1.14%)	87.5% → 88.6% (+1.11%)

Coverage comparison generated by scripts/ci/compare-coverage.ts

Copilot

Pull request overview

This PR fixes Docker-in-Docker (DinD) socket mounting for ARC/Kubernetes runners by deriving the bind-mounted Unix socket from configured Docker host settings instead of always assuming /var/run/docker.sock, improving compatibility with runners that expose Docker via a non-standard shared socket path.

Changes:

Added Unix-socket resolution logic for DinD mounts (with fallback + warnings for malformed unix:// values).
Updated agent volume mounting to only include /run/docker.sock when using the default socket path.
Added unit tests for custom Unix DOCKER_HOST, override precedence, and malformed Unix socket fallback; documented the ARC DinD sidecar pattern.

Show a summary per file

File	Description
src/services/agent-volumes.ts	Adds `resolveDockerSocketPath()` and updates DinD volume mounts to honor `unix://` socket paths (with fallback behavior).
src/services/agent-volumes.test.ts	Adds tests covering custom Unix socket mounts, precedence, and invalid Unix socket fallback behavior.
docs/environment.md	Documents ARC/Kubernetes runner pattern using a shared Unix Docker socket with `--enable-dind`.

Copilot's findings

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Comments suppressed due to low confidence (1)

src/services/agent-volumes.ts:36

socketPath is used verbatim in a docker volume spec (${dockerSocketPath}:/host${dockerSocketPath}:rw). If DOCKER_HOST contains trailing whitespace or unexpected characters like : or newlines, this can produce an invalid/misparsed mount string (and : could be interpreted as additional mount fields). It would be safer to trim() the extracted path and reject paths containing :/control characters before returning it.

  const socketPath = dockerHost.slice('unix://'.length);
  if (socketPath.startsWith('/') && socketPath !== '/' && socketPath.trim() !== '') {
    return socketPath;
  }

Files reviewed: 3/3 changed files
Comments generated: 3

+const DEFAULT_DOCKER_SOCKET_PATH = '/var/run/docker.sock';
+
+function resolveDockerSocketPath(config: WrapperConfig): string {
+  const dockerHost = config.awfDockerHost ?? process.env.DOCKER_HOST;


+    it('should prefer awfDockerHost over DOCKER_HOST when enableDind is true', () => {
+      const originalDockerHost = process.env.DOCKER_HOST;
+      process.env.DOCKER_HOST = 'unix:///tmp/arc/docker.sock';
+
+      try {
+        const dindConfig = {
+          ...mockConfig,
+          enableDind: true,
+          awfDockerHost: 'unix:///run/user/1000/docker.sock',
+        };
+        const result = generateDockerCompose(dindConfig, mockNetworkConfig);
+        const volumes = result.services.agent.volumes as string[];
+
+        expect(volumes).toContain('/run/user/1000/docker.sock:/host/run/user/1000/docker.sock:rw');
+        expect(volumes).not.toContain('/tmp/arc/docker.sock:/host/tmp/arc/docker.sock:rw');
+      } finally {


+On ARC self-hosted runners that expose Docker via a shared Unix socket volume instead of a TCP listener, set `DOCKER_HOST` to that Unix socket and enable DinD passthrough:
+
+```yaml
+env:
+  DOCKER_HOST: unix:///var/run/docker.sock
+steps:
+  - name: Run agent with AWF
+    run: |
+      awf --enable-dind --allow-domains github.com -- docker ps
+```
+
+When `DOCKER_HOST` points to a Unix socket, AWF now uses that socket path for DinD exposure instead of assuming `/var/run/docker.sock`. If your runner uses a different socket path, AWF will honor it automatically; `--docker-host unix:///path/to/docker.sock` remains the explicit override for AWF's own container operations.
+


lpcox · 2026-05-10T15:30:38Z

@copilot address the review feedback

Copilot · 2026-05-10T15:36:36Z

@copilot address the review feedback

Addressed in 4fc1383 with a follow-up test cleanup in b5bd01c.

lpcox

Review: PR #2841 — Honor Unix DOCKER_HOST sockets for DinD mounts

Verdict: ✅ Approve — clean, self-contained, no security concerns.

What I checked

resolveDockerSocketPath() validation — Correctly rejects TCP DOCKER_HOST values and falls back to /var/run/docker.sock. Only Unix socket paths are honored. Relative and empty paths are rejected with a warning.
/dev/null overlays untouched — The else block (DinD disabled) that mounts /dev/null over Docker sockets is completely unchanged. Security model preserved.
Fallback behavior — When DOCKER_HOST is missing, invalid, or TCP, defaults to /var/run/docker.sock. The /run/docker.sock symlink mount is correctly made conditional on default path only.
awfDockerHost precedence — --docker-host flag correctly takes priority over DOCKER_HOST env var.
Test coverage — Good: Unix socket exposure, flag precedence, invalid paths, agent DOCKER_HOST override. Minor gap: no explicit test for TCP DOCKER_HOST + enableDind (should fall back to default), but the logic is straightforward.

Staging note

This is the smallest and most self-contained of the three ARC/DinD PRs. Recommend merging first before #2843 and #2839 to minimize rebase conflicts.

github-actions · 2026-05-10T17:51:10Z

🔥 Smoke Test: Copilot BYOK (Offline) Mode

Test	Result
GitHub MCP connectivity	❌ (401 – GitHub MCP unauthenticated in this environment)
GitHub.com HTTP connectivity	✅ (pre-step confirmed)
File write/read	✅ (`BYOK smoke test passed at Sun May 10 17:49:37 UTC 2026`)
BYOK inference (api-proxy → api.githubcopilot.com)	✅ (prompt received and responded)

Running in BYOK offline mode (COPILOT_OFFLINE=true) via api-proxy → api.githubcopilot.com.

Overall: PASS (MCP auth failure is environment-level, not AWF/BYOK issue)

🔑 BYOK report filed by Smoke Copilot BYOK

github-actions · 2026-05-10T17:51:26Z

Smoke Test Results

❌ GitHub MCP Testing - gh CLI auth failed
✅ Playwright Testing - GitHub page title verified
✅ File Writing Testing - test file created
✅ Bash Tool Testing - file verified

Overall: FAIL (1/4 tests failed)

💥 [THE END] — Illustrated by Smoke Claude

github-actions · 2026-05-10T17:51:39Z

Smoke Test Results

Test	Status
GitHub MCP connectivity	❌ 401 Bad credentials
GitHub.com HTTP connectivity	⚠️ Template vars not expanded
File write/read (`smoke-test-copilot-25632715944.txt`)	✅ Content verified

Overall: FAIL — GitHub MCP returned 401 Bad credentials.

cc @Copilot

📰 BREAKING: Report filed by Smoke Copilot

github-actions · 2026-05-10T17:52:43Z

Smoke Test: Codex

Restore --ignore-scripts for engine CLI installs in lock files, add regression guard, install Claude native binary explicitly, and harden Smoke Codex safe-output targeting
api-proxy: set COPILOT_PROVIDER_WIRE_API=responses for GPT-5-family Copilot BYOK runs
GitHub PR review ✅ | safeinputs-gh ❌ | Playwright ✅ | Tavily ❌
File/bash ✅ | Discussion ❌ | Build ✅
Overall status: FAIL

Warning

Firewall blocked 1 domain

The following domain was blocked by the firewall during workflow execution:

registry.npmjs.org

To allow these domains, add them to the network.allowed list in your workflow frontmatter:

network:
  allowed:
    - defaults
    - "registry.npmjs.org"

See Network Configuration for more information.

🔮 The oracle has spoken through Smoke Codex

github-actions · 2026-05-10T17:53:08Z

Chroot Smoke Test Results

Runtime	Host Version	Chroot Version	Match?
Python	Python 3.12.13	Python 3.12.3	❌
Node.js	v24.14.1	v20.20.2	❌
Go	go1.22.12	go1.22.12	✅

Result: ❌ Not all versions matched — Go matches, but Python and Node.js differ between host and chroot environments.

Tested by Smoke Chroot

github-actions · 2026-05-10T17:53:29Z

🏗️ Build Test Suite Results

Ecosystem	Project	Build/Install	Tests	Status
Bun	elysia	✅	1/1 passed	✅ PASS
Bun	hono	✅	1/1 passed	✅ PASS
C++	fmt	✅	N/A	✅ PASS
C++	json	✅	N/A	✅ PASS
Deno	oak	N/A	1/1 passed	✅ PASS
Deno	std	N/A	1/1 passed	✅ PASS
.NET	hello-world	✅	N/A	✅ PASS
.NET	json-parse	✅	N/A	✅ PASS
Go	color	✅	1/1 passed	✅ PASS
Go	env	✅	1/1 passed	✅ PASS
Go	uuid	✅	1/1 passed	✅ PASS
Java	gson	✅	1/1 passed	✅ PASS
Java	caffeine	✅	1/1 passed	✅ PASS
Node.js	clsx	✅	passed	✅ PASS
Node.js	execa	✅	passed	✅ PASS
Node.js	p-limit	✅	passed	✅ PASS
Rust	fd	✅	1/1 passed	✅ PASS
Rust	zoxide	✅	1/1 passed	✅ PASS

Overall: 8/8 ecosystems passed — ✅ PASS

Generated by Build Test Suite for issue #2841 · ● 557K · ◷

github-actions · 2026-05-10T17:53:59Z

Smoke Test Results

Check	Result
Redis PING	❌ Timeout (no response)
PostgreSQL pg_isready	❌ No response
PostgreSQL SELECT 1	❌ Skipped (pg_isready failed)

Overall: FAIL — host.docker.internal is not reachable from this runner. Service containers may not be configured or this is a non-Docker runner environment.

🔌 Service connectivity validated by Smoke Services

The --docker-host-path-prefix flag from PR #2843 fully supersedes the --arc-dind feature. This merge brings in main (which includes #2841 and #2843) and removes the now-redundant arc-dind module and inline sourcePath() wrappers. Changes: - Delete src/arc-dind.ts and src/arc-dind.test.ts (orphaned) - Remove --arc-dind CLI option, config, schema, and docs - Remove sourcePath() wrappers from all service builders - Keep --docker-host-path-prefix with centralized translation in buildAgentVolumes() and kernel VFS passthrough (/dev, /sys, /proc) Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Initial plan

ef36e89

Copilot AI assigned Copilot and lpcox May 10, 2026

Copilot started work on behalf of lpcox May 10, 2026 14:04 View session

Copilot AI linked an issue May 10, 2026 that may be closed by this pull request

[awf] mcp-gateway: Docker socket not found on ARC DinD runners — DOCKER_HOST env var ignored #2836

Closed

Copilot AI added 4 commits May 10, 2026 14:09

fix: honor unix docker host for dind socket mounts

796e477

chore: finalize docker host dind fix

6ba3e2e

fix: tighten dind socket symlink mounts

358a5b0

fix: harden unix docker host fallback

ebaf9f3

Copilot AI changed the title ~~[WIP] Fix Docker socket not found issue on ARC DinD runners~~ Honor Unix DOCKER_HOST sockets for DinD mounts on ARC runners May 10, 2026

Copilot finished work on behalf of lpcox May 10, 2026 14:15

Copilot AI requested a review from lpcox May 10, 2026 14:15

lpcox marked this pull request as ready for review May 10, 2026 15:24

lpcox requested a review from Mossaka as a code owner May 10, 2026 15:24

Copilot AI review requested due to automatic review settings May 10, 2026 15:24

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Copilot started work on behalf of lpcox May 10, 2026 15:30 View session

Copilot AI added 2 commits May 10, 2026 15:34

fix: align agent docker host with dind override

4fc1383

test: restore docker host state in dind coverage

b5bd01c

Copilot finished work on behalf of lpcox May 10, 2026 15:37

lpcox approved these changes May 10, 2026

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This was referenced May 10, 2026

Fix chroot bind mounts for ARC/DinD split runner-daemon filesystems #2843

Merged

Add first-class ARC/DinD compatibility mode for AWF #2839

Merged

github-actions Bot added the smoke-copilot-byok label May 10, 2026

lpcox merged commit ad3020e into main May 10, 2026
66 of 71 checks passed

lpcox deleted the copilot/awf-fix-docker-socket-issue branch May 10, 2026 18:06

Copilot AI mentioned this pull request May 12, 2026

Auto-detect ARC/DinD and emit AWF --docker-host-path-prefix in generated workflows github/gh-aw#31614

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Bug Fix

What was the bug?

How did you fix it?

Socket path resolution

Agent Docker client alignment

Invalid config handling

Coverage and docs

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Review: PR #2841 — Honor Unix DOCKER_HOST sockets for DinD mounts

What I checked

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