rcourtman d5c7a3494b chore: remove deprecated Pulse+ agent metrics and add audit log rotation docs

Removed all legacy Pulse+ agent metrics infrastructure (cloud-relay) which has been
fully replaced by the new docker agent and temperature agent implementations.

Changes:
- Remove cloud-relay directory and all related binaries (relay, relay-linux, etc.)
- Remove Pulse+ documentation (AGENT_METRICS_IMPLEMENTATION.md, AGENT_METRICS_SETUP.md)
- Clean up pulse-relay references in workflows and release checklist
- Add audit log rotation documentation for sensor proxy hash-chained logs
- Update .gitignore to remove cloud-relay/ entry

The new docker and temp agents remain fully functional and unaffected by this cleanup.

2025-10-20 15:13:38 +00:00

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Pulse Sensor Proxy Audit Log Rotation

The sensor proxy writes a tamper-evident audit trail to /var/log/pulse/sensor-proxy/audit.log. Every entry includes the SHA-256 hash of the previous entry, so any modification becomes obvious. Because the process keeps the file open and maintains the running hash in memory, rotation requires special handling.

Rotation Strategy

Use logrotate to rotate the file once it reaches 100 MB. After each rotation, restart the proxy so it opens a new file and starts a fresh hash chain.

Create /etc/logrotate.d/pulse-sensor-proxy with the following contents:

/var/log/pulse/sensor-proxy/audit.log {
    daily
    size 100M
    rotate 90
    compress
    delaycompress
    missingok
    notifempty
    create 0640 pulse pulse
    sharedscripts
    postrotate
        systemctl restart pulse-sensor-proxy.service >/dev/null 2>&1 || true
    endscript
}

Why a Restart Is Mandatory

copytruncate and similar tricks break the chain integrity. Restarting the service ensures:

The proxy releases the old file descriptor.
A new hash chain starts at sequence 1 with an all-zero prev_hash.

If the proxy is not restarted, it will continue writing to the renamed file and the rotation will have no effect.

Chain Continuity Across Rotations

Each rotated log (audit.log.1.gz, audit.log.2.gz, …) is self-contained. To prove continuity between files:

After each rotation, record the final event_hash from the rotated file (for example, store it in the filename or a checksum manifest).
When reviewing logs, verify the prev_hash of the first entry in the new file is the zero hash, and reconcile the recorded final hash from the prior file to show no entries were removed.

Maintaining this “final hash ledger” allows auditors to stitch the rotated files together chronologically while preserving the tamper-evident guarantees.

Permissions

Adjust the create directive to match the user and group that run the sensor proxy. The example assumes both user and group are pulse.

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