Manage destination rules - Alibaba Cloud Service Mesh

When multiple versions of a service run simultaneously, you need to control how traffic behaves after it reaches the service -- which version receives requests, how load is distributed, and what happens when instances become unhealthy. Destination rules in Service Mesh (ASM) define these post-routing traffic policies, including load balancing, connection pool size from the sidecar, and outlier detection.

Virtual services control where traffic goes. Destination rules control how traffic behaves once it arrives. ASM evaluates virtual service routing rules first, then applies destination rule policies to the resolved destination.

DestinationRule fields

A destination rule consists of three core fields:

Field	Type	Description
`host`	string (required)	The service name from the Kubernetes service registry. Use fully qualified domain names (for example, `reviews.default.svc.cluster.local`) to avoid namespace ambiguity.
`trafficPolicy`	TrafficPolicy	Policies applied to all traffic for the host, including load balancing, connection pool limits, and outlier detection.
`subsets`	Subset[]	Named groups of service instances, typically differentiated by version labels. Each subset can override the default `trafficPolicy`.

Subset-level policies only take effect when a virtual service routing rule explicitly directs traffic to that subset.

For the full DestinationRule spec, see Destination Rule in the Istio documentation.

Create a destination rule

Prerequisites

Before you begin, make sure that you have:

An ASM instance. For more information, see [Create an ASM instance]()
At least one service deployed in the data plane cluster managed by the ASM instance

Procedure

Log on to the ASM console. In the left-side navigation pane, choose Service Mesh > Mesh Management.
On the Mesh Management page, click the name of the ASM instance. In the left-side navigation pane, choose Traffic Management Center > DestinationRule.
Create the destination rule using one of the following methods: The new destination rule appears in the list on the DestinationRule page.
- Console form: Click Create, configure the parameters, and click Create.
- YAML editor: Click Create from YAML. Select a namespace from the Namespace drop-down list and optionally a template from the Template drop-down list. Edit the YAML in the code editor, then click Create.

YAML examples

Define subsets by version

Group service instances into named subsets based on Kubernetes pod labels. A virtual service can then route traffic to specific subsets.

apiVersion: networking.istio.io/v1
kind: DestinationRule
metadata:
  name: reviews-destination
  namespace: default
spec:
  host: reviews.default.svc.cluster.local
  subsets:
  - name: v1
    labels:
      version: v1
  - name: v2
    labels:
      version: v2
  - name: v3
    labels:
      version: v3

Configure load balancing

Set a default load balancing algorithm for the service and override it for a specific subset.

apiVersion: networking.istio.io/v1
kind: DestinationRule
metadata:
  name: reviews-lb-policy
  namespace: default
spec:
  host: reviews.default.svc.cluster.local
  trafficPolicy:
    loadBalancer:
      simple: LEAST_REQUEST    # Default for all subsets
  subsets:
  - name: v1
    labels:
      version: v1
  - name: v2
    labels:
      version: v2
    trafficPolicy:
      loadBalancer:
        simple: ROUND_ROBIN    # Override for v2 only

The following load balancing algorithms are available:

Algorithm	When to use
`LEAST_REQUEST`	Distributes load to endpoints with the fewest outstanding requests.
`ROUND_ROBIN`	Simple rotation across endpoints. Use only when all endpoints have equal capacity and no weighting is needed.
`RANDOM`	Randomly selects a healthy host.
`PASSTHROUGH`	Forwards directly to the address requested by the caller without any load balancing.

Configure connection pooling and outlier detection

Limit connections to prevent cascading failures and automatically eject unhealthy hosts.

apiVersion: networking.istio.io/v1
kind: DestinationRule
metadata:
  name: reviews-circuit-breaker
  namespace: default
spec:
  host: reviews.default.svc.cluster.local
  trafficPolicy:
    connectionPool:
      tcp:
        maxConnections: 100           # Max TCP connections to the service
      http:
        h2UpgradePolicy: DEFAULT
        http1MaxPendingRequests: 100   # Max pending HTTP/1.1 requests
        http2MaxRequests: 1000        # Max concurrent HTTP/2 requests
    outlierDetection:
      consecutive5xxErrors: 5         # Eject after 5 consecutive 5xx errors
      interval: 30s                   # Health check interval
      baseEjectionTime: 30s           # Minimum ejection duration
      maxEjectionPercent: 50          # Eject at most 50% of hosts

Edit, roll back, or delete a destination rule

After you create a destination rule, the DestinationRule page lists all rules. The Actions column provides the following operations:

View or edit the YAML configuration: Click YAML. In the Edit dialog box, modify the configuration and click OK.
Roll back to a previous version: Click Version. In the Version dialog box, select a version and click Rollback.
Delete the destination rule: Click Delete. In the Submit message, click OK.
Important
Deleting a destination rule removes the associated load balancing, circuit breaking, and throttling policies, and unexpected issues may occur. Exercise caution when you delete a destination rule.

Alibaba Cloud Service Mesh:Manage destination rules