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moca-egress: async bounded audit, and bounded conn_cap refusals per VM

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
48/100
Issue type
Feature
Clarity
Mostly clear
Activity status
Active
Tech stack
go
Domain
backend, observability

Research direction

Read the #583 review discussion linked in the issue, then trace Audit.Emit, Unregister, abort(), and Close to see how audit writes interact with the proxy control socket. The issue proposes a bounded async audit queue with drop reporting, plus per-VM bounds and coalescing for conn_cap refusals. Done means audit stalls no longer block proxy operations and refusal handling stays bounded as described.

Written by the indexing model from the issue text.

Description

Follow-up from the #583 review (comment https://github.com/rossoctl/moca/pull/583#discussion_r4348544861), deferred out of that PR by agreement.

1. Cap refusals are unbounded. Each connection over MOCA_EGRESS_MAX_CONNS_PER_VM emits a conn_cap audit line and spawns a goroutine that holds the socket for up to ~2 s (writeAndClose: 1 s write plus 1 s drain). A guest connecting in a tight loop can:

  • exhaust host-wide fds in this single shared process (LimitNOFILE=65536);
  • flood stdout, so that journald's per-service rate limit (default 10000/30 s) drops other VMs' audit events.

Proposed: bound concurrent cap refusals per VM (close without drain on overflow), and coalesce conn_cap events per VM per interval.

2. Audit can stall the proxy. Audit.Emit writes synchronously to stdout and is called under pc.mu, including from abort() via Unregister. A stalled journald therefore blocks Unregister and Close, and with them the control socket. That contradicts the "auditing must not stall the proxy" comment.

Proposed: a bounded async queue with a drop counter, plus a periodic audit_dropped event when anything was dropped.

Related: #277, #583.

Dominant language
TypeScript
Stars
4
Forks
9
Avg merge
9h 31m
Merged PRs (30d)
139

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