Three issues fixed:
1. Memory metrics read host-side VmRSS of the Firecracker process,
which includes guest page cache and never decreases. Replaced
readMemRSS(fcPID) with readEnvdMemUsed(client) that queries
envd's /metrics endpoint for guest-side total - MemAvailable.
This matches neofetch and reflects actual process memory.
2. Added Firecracker balloon device (deflate_on_oom, 5s stats) and
envd-side periodic page cache reclaimer (drop_caches when >80%
used). Reclaimer is gated by snapshot_in_progress flag with
sync() before freeze to prevent memory corruption during pause.
3. Sampling interval 500ms → 1s, ring buffer capacities adjusted
to maintain same time windows. Reduces per-host HTTP load from
240 calls/sec to 120 calls/sec at 120 capsules.
Also: maxDiffGenerations 8 → 1 (merge every re-pause since UFFD
lazy-loads anyway), envd mem_used formula uses total - available.
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
- Change sandbox ID prefix from sb- to cl- (capsule) throughout
- Fix proxy URL regex character class: base36 uses 0-9a-z, not just hex
- Add MMDS V2 config and metadata to VM boot flow so envd can read
WRENN_SANDBOX_ID and WRENN_TEMPLATE_ID from inside the guest
- Pass TemplateID through VMConfig into both fresh and snapshot boot paths
Switch from the envd /init endpoint pushing host time via syscall to
chronyd reading the KVM PTP hardware clock (/dev/ptp0) continuously.
This fixes clock drift between init calls and handles snapshot resume
gracefully.
Changes:
- Add clocksource=kvm-clock kernel boot arg
- Start chronyd in wrenn-init.sh before tini (PHC /dev/ptp0, makestep 1.0 -1)
- Remove clock_settime logic from envd SetData and shouldSetSystemTime
- Remove client.Init() clock sync calls from sandbox manager (3 sites)
- Remove Init() method from envdclient (no longer needed)
- Simplify rootfs scripts: socat/chrony now come from apt in the container
image, only envd/wrenn-init/tini are injected by build scripts
Samples /proc/{fc_pid}/stat (CPU%), /proc/{fc_pid}/status (VmRSS), and
stat() on CoW files at 500ms intervals per running sandbox. Three tiered
ring buffers downsample into 30s and 5min averages for 10min/2h/24h
retention. Metrics are flushed to DB on pause (all tiers) and destroy
(24h only). New GetSandboxMetrics and FlushSandboxMetrics RPCs on the
host agent, proxied through GET /v1/sandboxes/{id}/metrics?range= on
the control plane. Returns live data for running sandboxes, DB data for
paused, and 404 for stopped.
Use Firecracker's Diff snapshot type when re-pausing a previously
resumed sandbox, capturing only dirty pages instead of a full memory
dump. Chains up to 10 incremental generations before collapsing back
to a Full snapshot. Multi-generation diff files (memfile.{buildID})
are supported alongside the legacy single-file format in resume,
template creation, and snapshot existence checks.
- 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
Implement full snapshot lifecycle: pause (snapshot + free resources),
resume (UFFD-based lazy restore), and named snapshot templates that
can spawn new sandboxes from frozen VM state.
Key changes:
- Snapshot header system with generational diff mapping (inspired by e2b)
- UFFD server for lazy page fault handling during snapshot restore
- Stable rootfs symlink path (/tmp/fc-vm/) for snapshot compatibility
- Templates DB table and CRUD API endpoints (POST/GET/DELETE /v1/snapshots)
- CreateSnapshot/DeleteSnapshot RPCs in hostagent proto
- Reconciler excludes paused sandboxes (expected absent from host agent)
- Snapshot templates lock vcpus/memory to baked-in values
- Proper cleanup of uffd sockets and pause snapshot files on destroy
Implement the host agent as a Connect RPC server that orchestrates
sandbox creation, destruction, pause/resume, and command execution.
Includes sandbox manager with TTL-based reaper, network slot allocator,
rootfs cloning, hostagent proto definition with generated stubs, and
test/debug scripts. Fix Firecracker process lifetime bug where VM was
tied to HTTP request context instead of background context.
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)
