Merge branch 'istio-docs-update' into 'master'

add istio/Architecture.md

See merge request platform-one/big-bang/bigbang!430

charter/packages/istio/Architecture.md

+# Istio
+
+## Overview
+
+[Istio](https://istio.io/latest/docs/concepts/what-is-istio/) is an open platform for providing a uniform way to [integrate microservices](https://istio.io/latest/docs/examples/microservices-istio/), manage [traffic flow](https://istio.io/latest/docs/concepts/traffic-management/) across microservices, enforce policies and aggregate telemetry data. Istio's control plane provides an abstraction
+layer over the underlying cluster management platform, such as Kubernetes.
+
+```mermaid
+graph LR
+  subgraph "Istio"
+    dataplane("Data Plane<br/>AKA Gateway") 
+    controlplane{{"Control Plane"}} --> dataplane
+    igw("Ingress Gateway") --"http 8080<br/>https 8443<br/>istiod 15012<br/>status 15021<br/>tls 15443"--> dataplane
+  end      
+
+  ig("Ingress") --> igw
+
+  subgraph "Monitoring"
+    svcmonitor("Service Monitor") --> controlplane
+    Prometheus --> svcmonitor("Service Monitor")
+  end
+  
+  subgraph "App"
+    dataplane --"app.bigbang.dev"<br/>port redirects--> appvs{{"Virtual Service"}} --> appsvc{{"App Service"}}
+  end
+
+  subgraph "Logging"
+    controlplane --> fluent(Fluentbit) --> logging-ek-es-http
+    logging-ek-es-http{{Elastic Service<br />logging-ek-es-http}} --> elastic[(Elastic Storage)]
+  end
+```
+
+## Big Bang Touchpoints
+
+### Licensing
+
+Istio is an open source tool that utilizes an Apache-2.0 License.
+
+### Storage
+
+Aside from the packages that it can integrate with, Istio provides no storage requirements.
+
+### High Availability
+
+By default, Istio is configured with 1 istiod replica, but it can be configured in the Big Bang values to use horizontal pod autoscaling:
+
+```yaml
+istio:
+  values:
+    istiod:
+      replicaCount: 1
+      hpaSpec:
+        minReplicas: 1
+        maxReplicas: 3
+```
+
+Likewise, the ingress gateway replicas can be specified and extra ingress gateways can be configured:
+
+```yaml
+istio:
+  values:
+    ingressGateway:
+      minReplicas: 1
+      maxReplicas: 5
+    extraIngressGateways:
+    # ...
+```
+
+### UI
+
+Big Bang can be configured to deploy [Kiali](https://repo1.dso.mil/platform-one/big-bang/apps/core/kiali) (a management console that provides dashboards, observability, and other robust capabilities) and [Jaeger](https://repo1.dso.mil/platform-one/big-bang/apps/core/jaeger) (an end-to-end distributed tracing system), both of which include UI features to help you visualize your Istio mesh. To enable Kialia and Jaeger, simply update the Big Bang values.yaml:
+
+```yaml
+istio:
+  enabled: true
+jaeger:
+  enabled: true
+kiali:
+  enabled: true
+```
+
+### Logging
+
+Within Big Bang, logs are captured by fluentbit and shipped to elastic by default.
+
+### Monitoring
+
+Monitoring can be enabled to automatically capture metrics for Istio when `monitoring.enabled` is set to `true` in the Big Bang values.yaml. Since Istio 1.5, standard metrics are directly exported by the Envoy proxy. For a list of metrics, see [Istio Standard Metrics](https://istio.io/latest/docs/reference/config/metrics/#metrics) and [Istio Observability](https://istio.io/latest/docs/ops/best-practices/observability/).
+
+Grafana (part of the monitoring packages) is a standalone component of Big Bang that can provide dashboards to show monitoring data. For more information, see Big Bang's [Grafana docs](https://repo1.dso.mil/platform-one/big-bang/apps/core/monitoring/-/tree/main/docs#grafana) and [Visualizing Metrics with Grafana](https://istio.io/latest/docs/tasks/observability/metrics/using-istio-dashboard/).
+
+### Healthchecks
+
+There are standard readiness probes built into the envoy sidecars and istio containers. See [here](https://istio.io/latest/docs/reference/config/istio.operator.v1alpha1/#ReadinessProbe) for more info.
+
+You can get events in an istio-injected naemspace to see if your sidecars are unhealthy or having issues. To check the health/status of the istio installation, run `kubectl get istiooperators -n istio-system`.
+
+### Dependant Packages
+
+- istio-operator
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