Network Troubleshooting
Flow logs, packet paths, and localising a problem to a hop.
6 to work through
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advanced
0.5% of requests time out. It is not correlated with any instance, endpoint, customer or time of day. Where do you look?
2 min answer -
advanced
A configuration push to thousands of edge locations must complete in under a minute, yet a bad config could take down the whole network. How do you reconcile speed with safety?
3 min answer -
advanced
A crypto exchange sees intermittent elevated latency to a market-data provider. Servers are healthy, the provider reports no issues, and the problem appears in bursts. How would you diagnose it?
2 min answer -
advanced
A developer platform receives reports that clones are slow "sometimes, from some places". Server metrics are healthy, error rates are normal, and the team cannot reproduce it. How do you investigate a problem that is invisible from the server side?
3 min answer -
advanced
A user reports intermittent TLS errors from one region only. Walk through your diagnosis.
2 min answer -
advanced
After moving a service behind a VPN to an on-premises system, small API calls succeed and large responses hang indefinitely. Walk through the diagnosis.
2 min answer
3 terms in this topic
Flow Logs
Records of accepted and rejected network connections, giving a queryable history of what actually talked to what.
conceptPath MTU Discovery
The mechanism by which a sender discovers the largest packet size a path supports, and a common cause of connections that establish and then hang.
conceptPath MTU Discovery Failure
Large packets silently discarded because the ICMP messages that would report the size limit are blocked - producing the signature "small requests wor…
Neighbouring topics
Networking
General material on the network path underneath an architecture.
TCP/IP
Handshakes, congestion control, head-of-line blocking and connection reuse.
HTTP/1.1, HTTP/2 & HTTP/3
Multiplexing, prioritisation and the transport each is built on.
DNS
Resolution, TTL behaviour, traffic steering and failover latency.
TLS & Certificates
Encryption, integrity, authentication, termination points and expiry.
Layer 4 vs Layer 7
Connection-level versus request-level balancing, and what each unlocks.
Reverse Proxies
One place for TLS, routing, caching, compression and rate limiting.
Content Delivery Networks
Edge caching, origin offload, spike absorption and dynamic content.
Firewalls & Security Groups
Default-deny, stateful rules, and restricting egress as well as ingress.
NAT & Egress
Outbound-only connectivity, its per-gigabyte cost and its zone binding.
VPC Design
Address planning, peering and the ranges you can never resize.
Subnetting
Tiering, zone binding, and sizing for an address-hungry platform.
Routing & BGP
How traffic finds you, anycast, and route withdrawal as a failure mode.
Service Mesh Networking
Sidecar proxies supplying mTLS, retries and traffic policy.
WebSockets & Realtime
Persistent bidirectional connections and the capacity model they impose.
gRPC Transport
HTTP/2 multiplexing, binary encoding and streaming semantics.
API Gateways
The single entry point, and the business logic that must stay out of it.
Network Performance
Latency floors, bandwidth-delay product, and what no code change fixes.
Private Connectivity
Private endpoints, peering and dedicated links to managed services.