[deepujain]

What

switchyard-server currently listens on every network interface when --host is omitted. This change defaults the standalone binary to 127.0.0.1. The Docker image, development systemd service, and Pier launch commands explicitly use --host 0.0.0.0 so those deployments remain reachable. A later --host overrides the Docker default.

Why

This reduces accidental network exposure. Existing remote deployments must add --host 0.0.0.0. Fixes #596.

Notes for reviewers

The two CLI regression tests fail with main's original CLI code and pass with this change. They cover the default address and later host overrides, including IPv6. The deployment guidance reflects the current supported launch paths.

Local validation passed on macOS with Rust 1.99 and Python 3.12:

• cargo fmt --all --check, workspace Clippy, and Clippy with prefill-router passed. cargo test --workspace --locked --offline passed 1,214 tests with one ignored. The prefill runner suite passed 133 tests.
• Ruff, mypy, actionlint, commitlint, the strict MkDocs build, and Rustdoc with warnings denied passed. uv run --no-sync pytest tests/ -v -m "not integration" -o addopts= passed 205 tests and two subtests, with two tests deselected.
• The rebuilt binary passed bind-and-health checks for the default, wildcard, and Docker argument override cases. Both current documented Pier launch commands passed --dry-run.

The existing handoff test remains ignored without PREFILL_ROUTER_HANDOFF_DIR. The Docker image, systemd execution, Go and TypeScript bindings, LiteLLM, packaging workflows, and other Python versions were not tested locally. No live provider calls or hosted E2E runs were made.

Summary by CodeRabbit

• Behavior Changes

  • The standalone server now listens only on the local machine by default. To accept remote connections, explicitly set the host to 0.0.0.0.
  • The provided Docker image and service configuration continue to bind to 0.0.0.0. A later host argument can override the Docker default.

• Documentation

  • Updated setup and command-line guidance to explain the default and remote-access configuration.

[coderabbitai]

No actionable comments were generated in the recent review.

Walkthrough

The standalone server now defaults to binding to 127.0.0.1. The Docker image, systemd service, and benchmark launch commands explicitly pass --host 0.0.0.0. Later --host arguments override earlier values.

Changes

Server binding behavior

Layer / File(s)	Summary
CLI host selection crates/switchyard-server/src/cli.rs	The default host changes to 127.0.0.1. A later --host value overrides earlier values. Tests cover the default and later values for IPv4, IPv6, and wildcard addresses.
Deployment host settings Dockerfile, dev-server/switchyard.service, benchmark/routing-profiles/*.toml, docs/cli_reference.md, CHANGELOG.md, crates/switchyard-server/README.md, docs/operations/local_evaluation.md	The Docker entrypoint, systemd service, and benchmark commands specify --host 0.0.0.0. Documentation describes the standalone default, remote-client host setting, and argument precedence.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: Minimal · up to 5ebc4

The standalone server now binds to loopback by default, and the Docker image, development service, and benchmark launch commands keep network access explicit. Existing remote deployments must add --host 0.0.0.0, which the PR documents. No merge-blocking risk remains.

Security architecture risk: Low · up to 18679

The default reduces accidental network exposure. The supplied remote-facing launchers preserve their previous reachability rather than adding authority. No introduced security concern was established, but protection of remotely reachable deployments remains dependent on their network and access controls.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

• inferred — For a wildcard-bound instance, potential exposure includes that process’s configured inference and fallback capabilities and its operational endpoints. Internet reachability, tenant scope, and the enabled downstream authority cannot be determined from the launch arguments alone. The PR preserves this exposure for the supplied remote launchers and reduces it for omitted-host standalone launches.

Security Findings and Attack Paths

• inferred — A client that can reach an inadequately protected wildcard listener can reach the existing inference and operational routes. This is a pre-existing conditional attack path, not an introduced PR concern: the base default was already wildcard, and the router is unchanged. Deployment-level enforcement remains unverified.

Trust Boundaries and Controls

• observed — The new default restricts network binding to IPv4 loopback; it does not add request authorization. The systemd launcher retains server-certificate TLS configuration, while caller access policy is not established by that configuration. Documentation explicitly instructs remote operators to secure access.

Resilience and Maintainability Implications

• observed — The selected address is fixed before serving. Bind failures return errors, and TLS initialization failure returns an error rather than retrying with plaintext. The host-default change does not introduce a recovery path that broadens the listener or weakens transport configuration.

Hardening Proposals

• proposed — For wildcard deployments, explicitly document and validate the authenticating ingress or network allowlist protecting both inference and operational routes. This is deployment hardening for an existing exposure, not a verified defect introduced by this PR.

Pre-merge checks: 4

Check name	Status	Explanation
Title check		The title clearly describes the loopback default and explicit deployment binding.
Linked Issues check		[#596] The CLI defaults to 127.0.0.1 and has regression tests for the default and host overrides. Docker and the development systemd service explicitly bind to 0.0.0.0. The documentation and changelog…
Out of Scope Changes check		[#596] The CLI, deployment commands, tests, documentation, and migration note support the bind-address change. The benchmark launch commands preserve remote reachability.
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.

Full details: Linked Issues check

Explanation

[#596] The CLI defaults to 127.0.0.1 and has regression tests for the default and host overrides. Docker and the development systemd service explicitly bind to 0.0.0.0. The documentation and changelog explain the default and migration for remote users.

• Autofix · Keep fixing CodeRabbit findings and required CI, and resolving merge conflicts

_{A rabbit checks the host at dawn
Loopback keeps the bind close in town
For wider paths, the flags say where
The Docker and service settings share
A later host can take the lead
Then off hops rabbit, pleased indeed!}

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• 🪄 Fix CodeRabbit comments on this PR

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Inline comments:
Review comments at @crates/switchyard-server/src/cli.rs:
- Around line 16-17: Update the DeepSWE launch-command comments associated with
DEFAULT_HOST and DEFAULT_PORT to include --host 0.0.0.0 for each listed Pier
workflow profile, so the documented commands bind to an address reachable from
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[eric-liu-nvidia]

Thanks for covering the whole set of deployment paths, not just the binary. I built the branch and checked the real binary. With no flag it binds 127.0.0.1. With --host 0.0.0.0 it binds all interfaces. A later --host after the image's default wins. /health answered in each case. Both new tests fail without the matching code change. The Docker image, systemd unit, Pier commands, run-baseline.sh, and the DeepSWE profiles all pass --host 0.0.0.0. The other docs examples use same-host clients, so they keep working.

Approving with one small request: please add a one-line comment on overrides_with = "host" in cli.rs saying it lets a later --host override the Docker ENTRYPOINT default. The test name explains it, but the attribute alone looks odd.

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Inline comments:
Review comments at @docs/operations/local_evaluation.md:
- Line 70: Update the network-access statement in the local evaluation
documentation to clarify that the systemd service generated by
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dev-server/switchyard.service if that is the intended service, or document the
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[ayushag-nv]

@deepujain Please rebase it and I can merge it then.

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