Here is the definition of Istio from its site, https://istio.io/:
"Istio addresses the challenges developers and operators face as monolithic applications transition toward a distributed microservice architecture."
With the increase in complexity of microservice architecture, it is mandatory to rely on resilience patterns, such as circuit breaking, load balancing, throttling, and so on.
Istio implements all of these behavioral patterns using pluggable policies via the Envoy proxy, which can be configured for the specific use case/policy at hand. Here is an example:
metadata:
name: circuit-breaker-policy
namespace: default
spec:
destination:
name: circuit-breaker
labels:
version: v1
circuitBreaker:
simple-circuit-breaker:
maxConnections: 100
httpMaxRequests: 1000
httpMaxRequestsPerConnection: 10
httpConsecutiveErrors: 7
sleepWindow: 15m
httpDetectionInterval: 5m
This means that a service mesh acts at application level (in network terms, L7), thus implementing retries, timeouts, circuit breaker, bulkheads, and routing control.