# Istio Agent

This document describes the internal architecture of Istio agent.

## High Level overview

![High Level overview](docs/overview.svg)

At a high level, the Istio agent acts as an intermediate proxy between Istiod and Envoy. This is done
at two levels. For distributing workload certificates, Envoy will send [SDS](https://www.envoyproxy.io/docs/envoy/latest/configuration/security/secret)

      for (Segment<K, V> segment : segments) {
        if (segment.count != 0) {
          return false;
        }
        sum -= segment.modCount;
      }
      return sum == 0L;
    }
    return true;
  }

  long longSize() {
    Segment<K, V>[] segments = this.segments;
    long sum = 0;
    for (Segment<K, V> segment : segments) {

      for (Segment<K, V> segment : segments) {
        if (segment.count != 0) {
          return false;
        }
        sum -= segment.modCount;
      }
      return sum == 0L;
    }
    return true;
  }

  long longSize() {
    Segment<K, V>[] segments = this.segments;
    long sum = 0;
    for (Segment<K, V> segment : segments) {
      sum += segment.count;
    }

}

type eventArgs struct {
	EventName    event.Name
	BucketName   string
	Object       ObjectInfo
	ReqParams    map[string]string
	RespElements map[string]string
	Host         string
	UserAgent    string
}

// ToEvent - converts to notification event.
func (args eventArgs) ToEvent(escape bool) event.Event {
	eventTime := UTCNow()
	uniqueID := fmt.Sprintf("%X", eventTime.UnixNano())

    if (hasLocalCache(cache)) {
      LocalCache<?, ?> map = toLocalCache(cache);
      for (Segment<?, ?> segment : map.segments) {
        drainRecencyQueue(segment);
      }
    }
  }

  static void drainRecencyQueue(Segment<?, ?> segment) {
    segment.lock();
    try {
      segment.cleanUp();
    } finally {
      segment.unlock();
    }
  }

  static void drainReferenceQueues(Cache<?, ?> cache) {

   * segments, each governed by its own write lock. The segment lock is taken once for each explicit
   * write, and twice for each cache loading computation (once prior to loading the new value, and
   * once after loading completes). Much internal cache management is performed at the segment
   * granularity. For example, access queues and write queues are kept per segment when they are

    AtomicReferenceArray<ReferenceEntry<Object, Object>> oldTable = segment.table;
    for (int i = 0; i < reps; i++) {
      // TODO(b/145386688): This access should be guarded by 'this.segment', which is not currently
      // held
      segment.expand();
      segment.table = oldTable;
      dummy += segment.count;
    }
    return dummy;
  }

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      "gridPos": {
        "h": 6,
        "w": 6,
        "x": 0,
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      },
      "hiddenSeries": false,
      "id": 55,
      "legend": {
        "avg": false,
        "current": false,
        "max": false,
        "min": false,
        "show": true,
        "total": false,
        "values": false
      },
      "lines": true,

      "fill": 1,
      "fillGradient": 0,
      "gridPos": {
        "h": 6,
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        "x": 0,
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      },
      "hiddenSeries": false,
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      "legend": {
        "avg": false,
        "current": false,
        "max": false,
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        "show": true,
        "total": false,
        "values": false
      },
      "lines": true,

          "pattern": "/^((?!critical|urgent).)*$/s"
        },
        {
          "type": "descriptionMatches",
          "pattern": "/^((?!critical|urgent).)*$/s"
        }
      ]
    }
  },
  "pr": {
    "critical": {
      "requires": 1,
      "conditions": [
        {
          "type": "descriptionMatches",
          "pattern": "/(critical|urgent)/i"
        },
        {