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ADR-004: Istio as Service Mesh

Status: Accepted

Date: 2026-01-25

Context

Need for secure communication between microservices and traffic observability.

Decision

Adopt Istio as Service Mesh with mTLS STRICT by default.

Rationale

Automatic mTLS between all services (zero-trust)
Native traffic observability (Grafana integration)
Resilience policies (retry, timeout, circuit breaker) via configuration
Maturity and active community

Consequences

Sidecar overhead in each pod (~50MB memory, ~50m CPU)
Additional complexity in troubleshooting
Need for team training