Running port-binding applications (Jupyter, http.server, NextJS) inside
sandboxes caused severe PTY sluggishness and proxy navigation errors.
Root cause: the CP sandbox proxy and Connect RPC pool shared a single
HTTP transport. Heavy proxy traffic (Jupyter WebSocket, REST polling)
interfered with PTY RPC streams via HTTP/2 flow control contention.
Transport isolation (main fix):
- Add dedicated proxy transport on CP (NewProxyTransport) with HTTP/2
disabled, separate from the RPC pool transport
- Add dedicated proxy transport on host agent, replacing
http.DefaultTransport
- Add dedicated envdclient transport with tuned connection pooling
- Replace http.DefaultClient in file streaming RPCs with per-sandbox
envd client
Proxy path rewriting (navigation fix):
- Add ModifyResponse to rewrite Location headers with /proxy/{id}/{port}
prefix, handling both root-relative and absolute-URL redirects
- Strip prefix back out in CP subdomain proxy for correct browser
behavior
- Replace path.Join with string concat in CP Director to preserve
trailing slashes (prevents redirect loops on directory listings)
Proxy resilience:
- Add dial retry with linear backoff (3 attempts) to handle socat
startup delay when ports are first detected
- Cache ReverseProxy instances per sandbox+port+host in sync.Map
- Add EvictProxy callback wired into sandbox Manager.Destroy
Buffer and server hardening:
- Increase PTY and exec stream channel buffers from 16 to 256
- Add ReadHeaderTimeout (10s) and IdleTimeout (620s) to host agent
HTTP server
Network tuning:
- Set TAP device TxQueueLen to 5000 (up from default 1000)
- Add Firecracker tx_rate_limiter (200 MB/s sustained, 100 MB burst)
to prevent guest traffic from saturating the TAP
Rename ns-{idx} to wrenn-ns-{idx} and veth-{idx} to wrenn-veth-{idx}
to avoid collisions with other tools. Add CleanupStaleNamespaces() at
agent startup to remove orphaned namespaces, veths, iptables rules, and
routes from a previous crash. Lower maxDiffGenerations from 10 to 8 to
prevent Go runtime memory corruption from snapshot/restore drift.
Add SafeName validator (allowlist regex) to reject directory traversal
in user-supplied template and snapshot names. Validated at both API
handlers (400 response) and sandbox manager (defense in depth).
Refactor CreateNetwork with rollback slice so partially created
resources (namespace, veth, routes, iptables rules) are cleaned up
on any error. Refactor RemoveNetwork to collect and return errors
instead of silently ignoring them.
- Replace reflink rootfs copy with device-mapper snapshots (shared
read-only loop device per base template, per-sandbox sparse CoW file)
- Add devicemapper package with create/restore/remove/flatten operations
and refcounted LoopRegistry for base image loop devices
- Fix pause ordering: destroy VM before removing dm-snapshot to avoid
"device busy" error (FC must release the dm device first)
- Add test UI at GET /test for sandbox lifecycle management (create,
pause, resume, destroy, exec, snapshot create/list/delete)
- Fix DirSize to report actual disk usage (stat.Blocks * 512) instead
of apparent size, so sparse CoW files report correctly
- Add timing logs to pause flow for performance diagnostics
- Fix all lint errors across api, network, vm, uffd, and sandbox packages
- Remove obsolete internal/filesystem package (replaced by devicemapper)
- Update CLAUDE.md with device-mapper architecture documentation
Add resolv.conf to wrenn-init so guests can resolve DNS, and fix the
host MASQUERADE rule to match vpeerIP (the actual source after namespace
SNAT) instead of hostIP.
Implements Phase 1: boot a Firecracker microVM, execute a command inside
it via envd, and get the output back. Uses raw Firecracker HTTP API via
Unix socket (not the Go SDK) for full control over the VM lifecycle.
- internal/vm: VM manager with create/pause/resume/destroy, Firecracker
HTTP client, process launcher with unshare + ip netns exec isolation
- internal/network: per-sandbox network namespace with veth pair, TAP
device, NAT rules, and IP forwarding
- internal/envdclient: Connect RPC client for envd process/filesystem
services with health check retry
- cmd/host-agent: demo binary that boots a VM, runs "echo hello", prints
output, and cleans up
- proto/envd: canonical proto files with buf + protoc-gen-connect-go
code generation
- images/wrenn-init.sh: minimal PID 1 init script for guest VMs
- CLAUDE.md: updated architecture to reflect TAP networking (not vsock)
and Firecracker HTTP API (not Go SDK)
