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headquarter/openspec/changes/archive/2026-05-22-instance-proxy/design.md
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Fusion 063a839790 feat: implement repository clone mode with SSH key support
- Add clone_mode and branch fields to tool_instances
- Add ssh_key_id to git_repositories for per-repo SSH key assignment
- Implement host-side git cloning with branch selection (default: main)
- Mount SSH keys into containers for git operations in clone mode
- Add dirty state check on clone-mode instance deletion with confirmation
- Update SessionsPage with mount/clone selector, branch input, SSH key display
- Add SSH key selector to repository creation form
- Add dirty delete confirmation modal with changed files list
- Update API schemas and endpoints for new fields
- Sync delta specs to main specs (git-repo, tool-instances, repo-clone-mode)
- Archive completed OpenSpec change: repo-clone-mode-with-ssh
- Document git requirement for custom tool types

Quality gates: Frontend typecheck and build passed
OpenSpec: repo-clone-mode-with-ssh archived with all tasks complete
2026-05-22 22:56:35 +02:00

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## Context
Currently, tool instances run as Docker containers on the internal Docker network. The backend stores their URL as `http://localhost:{port}`, which is only accessible from inside the API container. Users clicking "Open" in the frontend get a 404 because their browser can't reach the internal container.
The API and containers share a Docker network, so the API can reach containers by their container name or IP.
## Goals / Non-Goals
**Goals:**
- Users can access running tool instances through the API via HTTPS
- Proxy enforces ownership (only instance owner can access)
- Support both HTTP and WebSocket traffic
- Minimal latency overhead
- Works with existing Docker setup
**Non-Goals:**
- Public URLs / custom domains for instances (that's Option 2/3)
- Load balancing across multiple instances
- Advanced path rewriting (just pass-through)
## Decisions
### Proxy via FastAPI route (not separate service)
**Decision:** Implement proxying as a FastAPI endpoint using `httpx` for async forwarding.
**Rationale:**
- Keeps everything in one deployable unit
- Easy access to existing auth dependencies (`get_current_user_id`)
- Can reuse existing session cookie auth
- No extra infrastructure needed
**Alternative considered:** Separate nginx/traefik proxy service
- Rejected: adds operational complexity for a single feature
### Use container name for internal routing
**Decision:** Store container name in ToolInstance model and route to `http://{container_name}:{port}`
**Rationale:**
- Container names are stable and DNS-resolvable within Docker network
- More reliable than IPs which can change
- Already using container names in docker.py
### Path: `/instances/{id}/proxy/{path:path}`
**Decision:** All proxied traffic goes through `/instances/{id}/proxy/*`
**Rationale:**
- Clear URL structure
- Easy to apply auth middleware
- `path:path` captures everything after `/proxy/`
### WebSocket upgrade handling
**Decision:** Support WebSocket upgrade by inspecting the `Upgrade: websocket` header and establishing a bidirectional pipe.
**Rationale:**
- code-server and jupyter use WebSockets for real-time features
- FastAPI doesn't natively support proxying WebSockets, but we can use `starlette.websockets` to handle the upgrade
## Risks / Trade-offs
**[Risk]** API becomes bandwidth bottleneck for all instance traffic
**Mitigation:** Document this limitation. Future migration to Option 2 (Traefik labels) possible.
**[Risk]** Container name collision
**Mitigation:** Instance names already include UUID suffix, collision probability is negligible.
**[Risk]** Large file uploads/downloads through proxy
**Mitigation:** Use streaming response in httpx. Monitor memory usage.
## Migration Plan
1. Deploy backend changes (proxy endpoint + model updates)
2. Update frontend links to use proxy URL
3. Test with code-server instance
4. Monitor API performance
## Open Questions
- Should we add rate limiting to the proxy endpoint?
- Do we need to rewrite response headers (Location, Set-Cookie)?