troubleshoot-bind-dns

name	troubleshoot-bind-dns
description	Use when diagnosing issues with BIND DNS: recursive client exhaustion, cache pressure spiral, upstream dependency failure, udp packet drops, or zone staleness cascade. Queries Netdata via MCP for BIND DNS health signals, applies the diagnostic tree from the Netdata operator playbook, and recommends remediation.
version	0.1.0
author	Netdata
license	Apache-2.0
tags	["netdata","troubleshoot","mcp","bind-dns"]

Troubleshoot BIND DNS

When to use this skill

• Recursive client exhaustion: Outstanding fetches pile up (slow upstream), fill the recursive-clients table, new queries get SERVFAIL; cliff-edge failure.
• Cache pressure spiral: Undersized cache then low hit ratio then more upstream queries then more latency then more concurrent fetches then resource exhaustion.
• Upstream dependency failure: Forwarders or upstream nameservers slow/unreachable then queries hang for timeout duration (default 10s × 3 retries = 30s per slot) then slots consumed then broad SERVFAIL.
• UDP packet drops: Kernel receive buffer overflow then packets lost before BIND sees them then invisible query loss.
• Zone staleness cascade: Transfer failures then secondary serves stale data then SOA expire reached then zone removed then SERVFAIL/NXDOMAIN.
• DNSSEC time bomb: Signing stalls then signatures expire then validating resolvers worldwide reject zone then widespread SERVFAIL for signed domains.
• Any time the user reports a BIND DNS service behaving outside its expected envelope (elevated errors, latency, saturation, resource exhaustion, or unexpected restarts).
• An on-call engineer is paging on a Netdata alert tied to a BIND DNS instance and wants a structured triage path.

Key facts

• This skill wraps the Netdata operator playbook for BIND DNS. It does not replace the playbook; it routes a coding agent through MCP queries against the same signals the playbook relies on.
• BIND (named) is a single daemon that processes DNS queries through a pipeline: receive packet then parse then ACL/view check then cache lookup (if recursive) then zone lookup (if authoritative) then recursive fetch to upstream (if cache miss and recursion enabled) then apply RPZ/DNSSEC then serialize response then send.
• Dominant failure archetypes the playbook calls out: Recursive client exhaustion; Cache pressure spiral; Upstream dependency failure; UDP packet drops; Zone staleness cascade.
• Netdata observes the signals listed in the rule files via its native collectors, plus any OpenTelemetry-shipped metrics that your BIND DNS instrumentation adds. Both paths end at the same MCP query surface.

Step-by-step

1. Confirm the BIND DNS service is up. Query Netdata via MCP with list_nodes and filter by the host running the target. A missing node means the symptom is at the network or orchestrator layer, not inside the service.
2. Pull the last 15 minutes of signals for the target. Use query_metrics against the contexts listed in the domain rule files. Run find_anomalous_metrics in parallel over the same window; anomalies frame which rule file to read first.
3. Check for Recursive client exhaustion. Outstanding fetches pile up (slow upstream), fill the recursive-clients table, new queries get SERVFAIL; cliff-edge failure. Inspect the rule file whose signals move first for this mode.
4. Check for Cache pressure spiral. Undersized cache then low hit ratio then more upstream queries then more latency then more concurrent fetches then resource exhaustion. Inspect the rule file whose signals move first for this mode.
5. Check for Upstream dependency failure. Forwarders or upstream nameservers slow/unreachable then queries hang for timeout duration (default 10s × 3 retries = 30s per slot) then slots consumed then broad SERVFAIL. Inspect the rule file whose signals move first for this mode.
6. Check for UDP packet drops. Kernel receive buffer overflow then packets lost before BIND sees them then invisible query loss. Inspect the rule file whose signals move first for this mode.
7. Check for Zone staleness cascade. Transfer failures then secondary serves stale data then SOA expire reached then zone removed then SERVFAIL/NXDOMAIN. Inspect the rule file whose signals move first for this mode.
8. Correlate with host-level signals (system.cpu.utilization, system.memory.usage, system.disk.io_time). Many service-level failures have a host-resource precursor.
9. Apply the remediation hinted at in the matching rule file or the operator playbook. Re-run the MCP queries from the Verification section to confirm the signals returned to expected ranges. A fix that does not move the signal back is not a fix.

Handy MCP call templates

# Discover metrics from BIND DNS
list_metrics with q="bind-dns"

# Pull a specific context over the last window
query_metrics with context="bind-dns.*", relative_window=-15m

# Rank anomalies for the service or host
find_anomalous_metrics with node=<host> and context_pattern="bind-dns.*"

# Correlate a known problem context with others
find_correlated_metrics around the incident window

# Show current alert state
list_raised_alerts scoped to the node

Common mistakes

• Treating BIND DNS as a generic HTTP or process health check. BIND DNS has specific failure archetypes (see Key facts) that generic checks miss.
• Stopping at the first anomalous metric. Several archetypes produce correlated spikes; use find_correlated_metrics to widen the search before concluding a root cause.
• Quoting percentile latency without the sample count. Low traffic plus a single slow request moves p99 by seconds.
• Reading dashboards for a window shorter than the failure's fingerprint. Slow-brew failures (queue growth, bloat, memory fragmentation) need 30+ minutes of data to see the trend.
• Skipping the host-level correlation. A process-level fix for a noisy-neighbour problem does not hold.
• Assuming alert thresholds are tuned for your workload. Tune against observed BIND DNS traffic before escalating an alert configuration issue.

Verification

Netdata does not ship a native collector for BIND DNS; discovery is dynamic. Run these MCP queries against the Netdata instance that sees the BIND DNS service.

1. list_metrics with q="bind-dns" to discover contexts
2. query_metrics for each returned context over the last 30 minutes
3. find_anomalous_metrics scoped to the service or host

If list_metrics returns nothing for this service, instrumentation or scraping has not been set up yet. See skills/netdata-otel-setup/ or the relevant Netdata collector config reference.

When the fix does not hold

If signals drift back into the anomalous range within 30 minutes of a remediation, the cause was deeper than the applied change. Typical misdiagnoses for BIND DNS:

• Host-resource pressure masquerading as application bug.
• Dependent service (DB, cache, upstream) causing a secondary symptom in the instrumented service.
• Configuration change that was never reloaded (some subsystems only pick up config on full restart).

Escalate by widening the query window: 2-6 hours instead of 15 minutes. Slow-moving causes are invisible at triage window sizes.

References

• rules/overview.md
• Netdata operator playbook: the authoritative source material this skill summarizes.
• skills/netdata-mcp-integration/ for the transport setup.
• skills/netdata-otel-setup/ if additional application signals are needed beyond what Netdata collects natively.