Use ConcurrencyLimitingPolicy to implement request concurrency limiting - Alibaba Cloud Service Mesh

The ConcurrencyLimitingPolicy feature of the ASM traffic scheduling suite controls the number of concurrent requests sent to a service to prevent overload. The policy tracks in-flight requests and rejects new ones when the count exceeds a specified threshold.

Prerequisites

A Container Service for Kubernetes (ACK) managed cluster is added to your ASM instance, and the version of your ASM instance is V1.21.6.97 or later. For more information, see Add a cluster to an ASM instance.
Automatic sidecar proxy injection is enabled for the default namespace in the ACK cluster. For more information, see Manage global namespaces.
You have connected to the ACK cluster by using kubectl. For more information, see Connect to an ACK cluster using kubectl.
The ASM traffic scheduling suite is enabled. For more information, see Enable the ASM traffic scheduling suite.
The HTTPBin application is deployed and can be accessed by the sleep service over a gateway. For more information, see Deploy the HTTPBin application.

Step 1: Create a concurrency limiting policy by using ConcurrencyLimitingPolicy fields

Use kubectl to connect to the ASM instance. For more information, see Access Istio resources with kubectl.

Create a ConcurrencyLimitPolicy.yaml file that contains the following content:

apiVersion: istio.alibabacloud.com/v1
kind: ConcurrencyLimitingPolicy
metadata:
  name: concurrencylimit
  namespace: istio-system
spec:
  concurrency_limiter:
    max_concurrency: 1
    parameters:
      max_inflight_duration: 60s
    selectors:
    - service: httpbin.default.svc.cluster.local

The following table describes some of the fields. For more information, see ConcurrencyLimitingPolicy field reference.

Field	Description
max_concurrency	The maximum number of concurrent requests. In the example, this field is set to 1, which indicates that the service is allowed to process only one request at a time.
max_inflight_duration	The timeout period for request processing. If the ASM traffic scheduling suite fails to record a request termination event, for example, due to a pod restart, the request continues to count against the concurrency limit. This field marks requests that remain unresponsive beyond the specified duration as completed, preventing stale in-flight records from blocking new requests. Set this value based on the expected maximum response time. In this example, the field is set to 60s.
selectors	The services to which the concurrency limiting policy applies. In this example, the policy targets the httpbin.default.svc.cluster.local service.

Run the following command to enable the concurrency limiting policy:

kubectl apply -f ConcurrencyLimitingPolicy.yaml

Expected output:

concurrencylimitingpolicy.istio.alibabacloud.com/concurrencylimit created

Step 2: Verify that the concurrency limiting policy takes effect

Run the following command to open the shell command line for the sleep service:
```
kubectl exec -it deploy/sleep -- sh
```

Run the following commands to send a request from the backend that needs to take 30 seconds to complete, and then send a second request within 30 seconds.

curl httpbin:8000/delay/30 -I &
curl httpbin:8000 -I

Expected output:

HTTP/1.1 429 Too Many Requests
date: Fri, 26 Jul 2024 13:50:55 GMT
server: envoy
x-envoy-upstream-service-time: 1
transfer-encoding: chunked

~ $ HTTP/1.1 200 OK
server: envoy
date: Fri, 26 Jul 2024 13:51:05 GMT
content-type: application/json
content-length: 269
access-control-allow-origin: *
access-control-allow-credentials: true
x-envoy-upstream-service-time: 10006

[1]+  Done                       curl httpbin:8000/delay/30 -I

The second request receives an HTTP 429 status code, confirming that the concurrency limiting policy is in effect.

References

To monitor ConcurrencyLimitingPolicy on Grafana, make sure the Prometheus instance for Grafana is configured with the ASM traffic scheduling suite.

Import the following JSON into Grafana to create a ConcurrencyLimitingPolicy dashboard.

Click to view details

{
  "annotations": {
    "list": [
      {
        "builtIn": 1,
        "datasource": {
          "type": "grafana",
          "uid": "-- Grafana --"
        },
        "enable": true,
        "hide": true,
        "iconColor": "rgba(0, 211, 255, 1)",
        "name": "Annotations & Alerts",
        "type": "dashboard"
      }
    ]
  },
  "editable": true,
  "fiscalYearStartMonth": 0,
  "graphTooltip": 0,
  "id": 41,
  "links": [],
  "liveNow": false,
  "panels": [
    {
      "datasource": {
        "type": "prometheus",
        "uid": "${datasource}"
      },
      "description": "Signal derived from periodic execution of query: (sum(rate(concurrency_limiter_counter_total{policy_name=\"concurrencylimit\",component_id=\"root.0\",decision_type=\"DECISION_TYPE_ACCEPTED\"}[30s])) / sum(rate(concurrency_limiter_counter_total{policy_name=\"concurrencylimit\",component_id=\"root.0\"}[30s]))) * 100",
      "fieldConfig": {
        "defaults": {
          "color": {
            "mode": "palette-classic"
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          "custom": {
            "axisCenteredZero": false,
            "axisColorMode": "text",
            "axisLabel": "",
            "axisPlacement": "auto",
            "barAlignment": 0,
            "drawStyle": "line",
            "fillOpacity": 10,
            "gradientMode": "none",
            "hideFrom": {
              "legend": false,
              "tooltip": false,
              "viz": false
            },
            "lineInterpolation": "linear",
            "lineWidth": 1,
            "pointSize": 5,
            "scaleDistribution": {
              "type": "linear"
            },
            "showPoints": "auto",
            "spanNulls": false,
            "stacking": {
              "group": "A",
              "mode": "none"
            },
            "thresholdsStyle": {
              "mode": "off"
            }
          },
          "mappings": [],
          "thresholds": {
            "mode": "absolute",
            "steps": [
              {
                "color": "green",
                "value": null
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              {
                "color": "red",
                "value": 80
              }
            ]
          },
          "unit": ""
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        "overrides": []
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      "gridPos": {
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        "w": 24,
        "x": 0,
        "y": 0
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      "id": 1,
      "interval": "10s",
      "options": {
        "legend": {
          "calcs": [],
          "displayMode": "list",
          "placement": "bottom",
          "showLegend": true
        },
        "tooltip": {
          "mode": "single",
          "sort": "none"
        }
      },
      "pluginVersion": "v10.1.0",
      "targets": [
        {
          "datasource": {
            "type": "prometheus",
            "uid": "${datasource}"
          },
          "editorMode": "code",
          "expr": "(sum by (policy_name) (rate(concurrency_limiter_counter_total{component_id=\"root.0\",decision_type=\"DECISION_TYPE_ACCEPTED\"}[30s])) / sum by (policy_name) (rate(concurrency_limiter_counter_total{component_id=\"root.0\"}[30s]))) * 10",
          "intervalFactor": 1,
          "legendFormat": "accepted percentage",
          "range": true,
          "refId": "A"
        }
      ],
      "title": "Accept Percentage",
      "type": "timeseries"
    },
    {
      "datasource": {
        "type": "prometheus",
        "uid": "${datasource}"
      },
      "fieldConfig": {
        "defaults": {
          "color": {
            "mode": "thresholds"
          },
          "mappings": [],
          "noValue": "No data",
          "thresholds": {
            "mode": "absolute",
            "steps": [
              {
                "color": "blue",
                "value": null
              }
            ]
          },
          "unit": "short"
        },
        "overrides": []
      },
      "gridPos": {
        "h": 10,
        "w": 8,
        "x": 0,
        "y": 10
      },
      "id": 2,
      "options": {
        "colorMode": "value",
        "graphMode": "area",
        "justifyMode": "center",
        "orientation": "horizontal",
        "reduceOptions": {
          "calcs": [
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          "fields": "",
          "values": false
        },
        "textMode": "auto"
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      "pluginVersion": "10.0.9",
      "targets": [
        {
          "datasource": {
            "type": "prometheus",
            "uid": "${datasource}"
          },
          "editorMode": "code",
          "expr": "sum by (policy_name) (increase(concurrency_limiter_counter_total{component_id=\"root.0\"}[$__range]))",
          "instant": false,
          "intervalFactor": 1,
          "legendFormat": "{{ policy_name }}",
          "range": true,
          "refId": "A"
        }
      ],
      "title": "Total Requests",
      "type": "stat"
    },
    {
      "datasource": {
        "type": "prometheus",
        "uid": "${datasource}"
      },
      "fieldConfig": {
        "defaults": {
          "color": {
            "mode": "thresholds"
          },
          "mappings": [],
          "noValue": "No data",
          "thresholds": {
            "mode": "absolute",
            "steps": [
              {
                "color": "green",
                "value": null
              }
            ]
          },
          "unit": "short"
        },
        "overrides": []
      },
      "gridPos": {
        "h": 10,
        "w": 8,
        "x": 8,
        "y": 10
      },
      "id": 3,
      "options": {
        "colorMode": "value",
        "graphMode": "area",
        "justifyMode": "center",
        "orientation": "horizontal",
        "reduceOptions": {
          "calcs": [
            "lastNotNull"
          ],
          "fields": "",
          "values": false
        },
        "textMode": "auto"
      },
      "pluginVersion": "10.0.9",
      "targets": [
        {
          "datasource": {
            "type": "prometheus",
            "uid": "${datasource}"
          },
          "editorMode": "code",
          "expr": "sum by (policy_name)(increase(concurrency_limiter_counter_total{component_id=\"root.0\", decision_type=\"DECISION_TYPE_ACCEPTED\"}[$__range]))",
          "instant": false,
          "intervalFactor": 1,
          "legendFormat": "{{ policy_name }}",
          "range": true,
          "refId": "A"
        }
      ],
      "title": "Total Accepted Requests",
      "type": "stat"
    },
    {
      "datasource": {
        "type": "prometheus",
        "uid": "${datasource}"
      },
      "fieldConfig": {
        "defaults": {
          "color": {
            "mode": "thresholds"
          },
          "mappings": [],
          "noValue": "No rejected requests",
          "thresholds": {
            "mode": "absolute",
            "steps": [
              {
                "color": "red",
                "value": null
              }
            ]
          },
          "unit": "short"
        },
        "overrides": []
      },
      "gridPos": {
        "h": 10,
        "w": 8,
        "x": 16,
        "y": 10
      },
      "id": 4,
      "options": {
        "colorMode": "value",
        "graphMode": "area",
        "justifyMode": "center",
        "orientation": "horizontal",
        "reduceOptions": {
          "calcs": [
            "lastNotNull"
          ],
          "fields": "",
          "values": false
        },
        "textMode": "auto"
      },
      "pluginVersion": "10.0.9",
      "targets": [
        {
          "datasource": {
            "type": "prometheus",
            "uid": "${datasource}"
          },
          "editorMode": "code",
          "expr": "sum by (policy_name)(increase(concurrency_limiter_counter_total{component_id=\"root.0\", decision_type=\"DECISION_TYPE_REJECTED\"}[$__range]))",
          "instant": false,
          "intervalFactor": 1,
          "legendFormat": "{{ instance }} - {{ policy_name }}",
          "range": true,
          "refId": "A"
        }
      ],
      "title": "Total Rejected Requests",
      "type": "stat"
    },
    {
      "datasource": {
        "type": "prometheus",
        "uid": "${datasource}"
      },
      "description": "",
      "fieldConfig": {
        "defaults": {
          "color": {
            "mode": "palette-classic"
          },
          "custom": {
            "axisCenteredZero": false,
            "axisColorMode": "text",
            "axisLabel": "Decisions",
            "axisPlacement": "auto",
            "barAlignment": 0,
            "drawStyle": "line",
            "fillOpacity": 10,
            "gradientMode": "none",
            "hideFrom": {
              "legend": false,
              "tooltip": false,
              "viz": false
            },
            "lineInterpolation": "linear",
            "lineWidth": 1,
            "pointSize": 5,
            "scaleDistribution": {
              "type": "linear"
            },
            "showPoints": "auto",
            "spanNulls": false,
            "stacking": {
              "group": "A",
              "mode": "none"
            },
            "thresholdsStyle": {
              "mode": "off"
            }
          },
          "mappings": [],
          "thresholds": {
            "mode": "absolute",
            "steps": [
              {
                "color": "green",
                "value": null
              },
              {
                "color": "red",
                "value": 80
              }
            ]
          },
          "unit": "reqps"
        },
        "overrides": []
      },
      "gridPos": {
        "h": 10,
        "w": 24,
        "x": 0,
        "y": 20
      },
      "id": 5,
      "interval": "10s",
      "options": {
        "legend": {
          "calcs": [],
          "displayMode": "list",
          "placement": "bottom",
          "showLegend": true
        },
        "tooltip": {
          "mode": "single",
          "sort": "none"
        }
      },
      "pluginVersion": "v10.1.0",
      "targets": [
        {
          "datasource": {
            "type": "prometheus",
            "uid": "${datasource}"
          },
          "editorMode": "code",
          "expr": "sum by(decision_type, policy_name) (rate(concurrency_limiter_counter_total{component_id=\"root.0\"}[$__rate_interval]))",
          "intervalFactor": 1,
          "range": true,
          "refId": "A"
        }
      ],
      "title": "Concurrency Limiter Decision Overview",
      "type": "timeseries"
    }
  ],
  "refresh": "",
  "schemaVersion": 38,
  "style": "dark",
  "tags": [],
  "templating": {
    "list": [
      {
        "hide": 0,
        "includeAll": false,
        "label": "Data Source",
        "multi": false,
        "name": "datasource",
        "options": [],
        "query": "prometheus",
        "refresh": 1,
        "regex": "",
        "skipUrlSync": false,
        "type": "datasource"
      }
    ]
  },
  "time": {
    "from": "now-5m",
    "to": "now"
  },
  "timepicker": {},
  "timezone": "browser",
  "title": "Policy Summary - concurrencylimit",
  "version": 1,
  "weekStart": ""
}

The following figure shows the dashboard.