What is a service mesh and what does Istio add?
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Quick Answer
A service mesh handles service-to-service traffic (routing, security, observability) via sidecar proxies, offloading it from application code.
Detailed Answer
Istio injects an Envoy sidecar next to each pod that intercepts all traffic. This gives you mTLS, traffic routing, retries, timeouts, and telemetry uniformly, without changing app code. The control plane (istiod) configures the proxies; the data plane (Envoy sidecars) enforces the rules.
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Interview Tip
Separate control plane (istiod) from data plane (Envoy).
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