troubleshoot-envoy

name	troubleshoot-envoy
description	Use when diagnosing issues with Envoy: connection pool exhaustion cascade, memory pressure spiral, xds control plane disconnect, retry amplification, or stats cardinality explosion. Queries Netdata via MCP for server state, upstream host health, upstream request rate, downstream request rate, upstream request duration, 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","envoy"]

Troubleshoot Envoy

When to use this skill

• Connection pool exhaustion cascade: Upstream is slow then connections held longer then pool fills then pending requests queue then queue overflows then 503s with response flag UO. Envoy appears "broken" but is protecting itself from the upstream.
• Memory pressure spiral: Large request/response bodies + buffering filters then heap grows then overload manager triggers then starts refusing connections then cascading backpressure.
• xDS control plane disconnect: Control plane goes down then Envoy keeps running with last-known-good config then new services/endpoints invisible then stale routing then silent misrouting or 503s for new services.
• Retry amplification: Aggressive retry config then upstream partial failure then retry storm multiplies load 2x-3x then accelerates the failure retries are trying to mask.
• Stats cardinality explosion: Dynamic route names or per-request metadata in stats tags then stats memory region fills then new stats silently fail to register then monitoring blind spots.
• Hot restart race conditions: New process starts before old finishes draining then brief period where neither process is fully healthy then connection drops during rollover.
• Any time the user reports a Envoy 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 Envoy instance and wants a structured triage path.

Key facts

• This skill wraps the Netdata operator playbook for Envoy. It does not replace the playbook; it routes a coding agent through MCP queries against the same signals the playbook relies on.
• Envoy is a multi-threaded, event-driven L4/L7 proxy written in C++. At runtime, it is continuously doing these things:
• • Accepting downstream TCP connections on listener sockets - Parsing protocols and applying filter chains (network filters then HTTP connection manager then HTTP filters then router) - Routing requests/streams to upstream clusters based on route tables - Managing per-worker, per-cluster, per-host upstream connection pools - Buffering request and response data through filter chains - Enforcing t...
• The playbook decomposes Envoy health into 7 signal domains: Availability, Throughput, Latency, Errors, Saturation, Internal State. Each domain maps to one rule file in this skill.
• Dominant failure archetypes the playbook calls out: Connection pool exhaustion cascade; Memory pressure spiral; xDS control plane disconnect; Retry amplification; Stats cardinality explosion.
• Netdata observes the signals listed in the rule files via its native collectors, plus any OpenTelemetry-shipped metrics that your Envoy instrumentation adds. Both paths end at the same MCP query surface.
• Netdata's envoy collector emits 54 context(s) under envoy.*. The rule files enumerate which contexts surface which domain; the Verification section below names the load-bearing ones explicitly.

Step-by-step

1. Confirm the Envoy 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 Connection pool exhaustion cascade. Upstream is slow then connections held longer then pool fills then pending requests queue then queue overflows then 503s with response flag UO. Envoy appears "broken" but is protecting itself from the upstream. Inspect the rule file whose signals move first for this mode.
4. Check for Memory pressure spiral. Large request/response bodies + buffering filters then heap grows then overload manager triggers then starts refusing connections then cascading backpressure. Inspect the rule file whose signals move first for this mode.
5. Check for xDS control plane disconnect. Control plane goes down then Envoy keeps running with last-known-good config then new services/endpoints invisible then stale routing then silent misrouting or 503s for new services. Inspect the rule file whose signals move first for this mode.
6. Check for Retry amplification. Aggressive retry config then upstream partial failure then retry storm multiplies load 2x-3x then accelerates the failure retries are trying to mask. Inspect the rule file whose signals move first for this mode.
7. Check for Stats cardinality explosion. Dynamic route names or per-request metadata in stats tags then stats memory region fills then new stats silently fail to register then monitoring blind spots. 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 Envoy
list_metrics with q="envoy"

# Pull a specific context over the last window
query_metrics with context="envoy.server_connections_count", relative_window=-15m

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

# 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 Envoy as a generic HTTP or process health check. Envoy 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 Envoy traffic before escalating an alert configuration issue.

Verification

Run these MCP queries against the Netdata instance that sees the Envoy service. Every context listed below is a real Netdata chart name; the agent does not need to guess.

1. list_metrics filtered by q="envoy" (returns every envoy.* context Netdata sees)
2. query_metrics with contexts=[envoy.server_connections_count, envoy.server_parent_connections_count, envoy.server_uptime, envoy.cluster_manager_cluster_updates_rate, envoy.cluster_manager_cluster_updated_via_merge_rate, envoy.cluster_manager_update_merge_cancelled_rate] and relative_window=-30m
3. find_anomalous_metrics filtered by node=<host> and context_pattern="envoy.*"

Load-bearing contexts for this service:

• envoy.server_connections_count: Server current connections (connections). Dimensions: connections.
• envoy.server_parent_connections_count: Server current parent connections (connections). Dimensions: connections.
• envoy.server_uptime: Server uptime (seconds). Dimensions: uptime.
• envoy.cluster_manager_cluster_updates_rate: Cluster manager updates (updates/s). Dimensions: cluster.
• envoy.cluster_manager_cluster_updated_via_merge_rate: Cluster manager updates applied as merged updates (updates/s). Dimensions: via_merge.
• envoy.cluster_manager_update_merge_cancelled_rate: Cluster manager cancelled merged updates (updates/s). Dimensions: merge_cancelled.

A clean result means every context is within its expected band and the find_anomalous_metrics list is empty or contains only already-acknowledged items. If the fix was real, re-running the same queries 10 minutes after applying it will show a clean result. If it does not, revert and look deeper.

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 Envoy:

• 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/availability.md
• rules/throughput.md
• rules/latency.md
• rules/errors.md
• rules/saturation.md
• rules/internal-state.md
• rules/configuration-state.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.