I've been running Falcon sensors on a subset of our AWS VMs for about 8 months, mostly for evaluation. Lately, I've hit a snag that's eating up my troubleshooting time and I'm wondering if anyone else has mapped out the failure points.
The scenario: The Falcon sensor UI on the host shows a green 'Operational' or 'Online' status. No visible errors locally. However, in the Falcon cloud console, that host shows as 'Offline' or the last event timestamp is hours/days old. The sensor process (`csfalcon`) is running. This creates a dangerous blind spot.
From my packet capture and log digging so far, here's what I've ruled out and what I'm still stuck on:
* **It's not a simple proxy issue.** We have direct outbound HTTPS (443) to CrowdStrike's domains allowed, and `tsupport.falcon.crowdstrike.com` connectivity tests pass from the host.
* **Sensor version mismatch?** All hosts are on the same minor version (6.70.x). I've ruled out a known bad update.
* **Resource exhaustion?** System metrics (CPU, memory, disk) on the affected hosts are normal. No cgroup or ulimit hits I can find.
My current hypothesis points to one of these less-documented areas:
* **Internal queue backlog within the sensor:** Could events be stuck in a local buffer due to some parsing failure? If so, what's the best way to confirm and flush it without a full sensor reinstall?
* **Clock skew or TLS certificate validation:** Could even a minor time drift (30+ seconds) between host and CrowdStrike backend cause the heartbeat to fail, while the sensor *thinks* it's healthy?
* **A specific, blocked IP range:** Our allowlist is based on CrowdStrike's published CIDRs. Has anyone had to add netblocks not on their official list to get reliable heartbeats?
What I'm looking for is any internal log location (beyond the standard `/var/log/csfalcon.log`) or a diagnostic command that can show the sensor's actual connection state and outbound queue depth. The whole point of a lightweight sensor is that it *just works*, so this kind of "silent failure" mode is concerning for cost-per-protected-endpoint.
Has anyone built a systematic checklist for this, or found a specific pattern (e.g., happens on ARM instances, after certain kernel live-patches, etc.)?
That internal queue backlog theory is interesting. I saw something similar with a different agent-based security tool last year. The local process was happy, but a silent disk I/O bottleneck on the audit logs meant events just piled up and never shipped.
For your case, have you checked the sensor's own debug logs? I think there's a `csfalcon` command with a `--debug` flag that can show the queue status, which might not be in the main system logs. Could be a permission issue on the spool directory too, maybe after a host disk resize?
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