# Proxyless Service Mesh Based on Sermant and Istio

This article primarily introduces the concepts, deployment patterns, and specific capabilities of the Sermant + Istio proxyless service mesh. These capabilities are implemented based on the xDS Core Service (opens new window) of the Sermant framework layer.

# Service Governance of Sermant in Istio Environment

A service mesh is an infrastructure layer that handles service-to-service communication. It reliably delivers requests through the complex service topology that constitutes modern cloud-native applications. In practice, service mesh is usually implemented as a lightweight array of network proxies, which are deployed alongside application code, without the application being aware of the presence of these proxies.

Istio is currently the most widely used Service Mesh product, consisting of a control plane and a data plane. The data plane in Istio typically deploys separate sidecar containers to proxy microservices, resulting in additional performance overhead, including increased CPU usage and significant growth in service call latency. Additionally, this setup increases system complexity and the difficulty of operations and maintenance.

The Sermant xDS service allows microservices to integrate with Istio in a Kubernetes environment. Sermant communicates directly with Istio's control plane based on the xDS protocol to obtain configuration information such as service discovery and routing, thereby replacing Envoy as Istio's data plane for service governance.

Sermant is a cloud-native, proxyless service mesh based on a Java Agent. Microservices run Sermant in the same process, eliminating the need to start additional sidecar containers for network proxying. This significantly reduces application performance overhead and call latency between services.

# Istio+Sermant Sidecar Proxyless Mode Deployment

Mixed Deployment Mode: Coexistence of Sidecar Proxy Mode and Sidecar Proxyless Mode. Microservices connect to Istio and achieve service governance through a mixed deployment mode. This mode avoids modifying the existing deployment architecture, allowing only new services to use the Sidecar Proxyless Mode.
Proxyless Deployment Mode: All microservices use Sermant as Istio's data plane to achieve capabilities such as service discovery、routing and load balancing. Sermant can replace the capabilities provided by Envoy, currently supporting service discovery, with more features to be developed in the future.

# Advantages of using Sermant in Istio Environment

Sermant runs in the same process as microservices, eliminating the need to start additional sidecar containers, significantly reducing network call latency and CPU overhead.
Developing plugins based on the Sermant framework can achieve richer governance capabilities than Envoy, offering greater extensibility.
Lower architectural complexity leads to reduced deployment costs.

# Service Discovery based on xDS Service

In a Kubernetes environment, users can create Pods and Services through custom resource files using Deployment (opens new window) and Service (opens new window). The Sermant framework implements service discovery capabilities based on the xDS protocol. Plugins can call the xDS service discovery interface to obtain instances of Kubernetes Service . For detailed development guidance, please refer to Service Discovery Development Guide Based on xDS Services.

# Template for Creating Pod and Service in Kubernetes

Deployment:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: spring-test
  labels:
    app: spring-test
spec:
  replicas: 1
  selector:
    matchLabels:
      app: spring-test
  template:
    metadata:
      labels:
        app: spring-test
    spec:
      containers:
      - name: spring-test
        image: spring-test:1.0.0
        ports:
        - containerPort: 8003

Service:

apiVersion: v1
kind: Service
metadata:
  name: spring-test
spec:
  type: ClusterIP
  ports:
  - name: test
    port: 8003
    targetPort: 8003
    protocol: TCP
  selector:
    app: spring-test

Note: Sermant uses the metadata.name of the Service resource file as the service name for service discovery.

# Sermant Plugins Supportting xDS Service Discovery

Router Plugin

# Routing based on xDS Service

The Sermant framework implements the ability to retrieve routing configurations based on the xDS protocol. Plugins can call the xDS routing configuration service interface to obtain routing configurations for Kubernetes Services. For specific development guidance, please refer to Development Guide for Routing Configuration Service Based on xDS.

# Supported Istio Routing Configuration Fields

Istio delivers routing configurations via custom resource files such as DestinationRule and VirtualService. Sermant communicates with Istio's control plane via the xDS protocol to obtain routing configurations. The following are the supported routing configuration fields:

VirtualService:

Supported Fields	Description
spec.hosts	The service domain of the route
spec.hosts.http	HTTP route configuration
spec.hosts.http.match	HTTP route matching rules
spec.hosts.http.match.headers	HTTP header matching rules, supporting exact, prefix, and regex matches
spec.hosts.http.match.uri	HTTP URI matching rules, supporting exact, prefix, and regex matches
spec.hosts.http.match.ignoreUriCase	HTTP URI case-insensitive matching
spec.hosts.http.route	HTTP route
spec.hosts.http.route.destination	HTTP route destination service
spec.hosts.http.route.destination.host	Domain name of the destination service
spec.hosts.http.route.destination.subset	Subset of the destination service
spec.hosts.http.route.destination.port.number	Port of the destination service
spec.hosts.http.route.weight	Weight of the destination service

DestinationRule:

Supported Fields	Description
spec.trafficPolicy	Traffic policy
spec.trafficPolicy.loadBalancer	Load balancing policy
spec.trafficPolicy.loadBalancer.localityLbSetting.enabled	Same AZ routing configuration

# Istio Routing Configuration Template

VirtualService:

apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: spring-test-virtualservice
spec:
  hosts:
  - spring-test
  http:
  - name: "v1-routes"
    match:
    - headers:
        version:
          exact: v1
      uri:
        exact: /test
      ignoreUriCase: false
    route:
    - destination:
        host: spring-test
        subset: v1
        port:
          number: 8003
      weight: 100
  - name: "base-route"
    route:
    - destination:
        host: spring-test
        subset: base
        port:
          number: 8003

Description: For the upstream service with the name spring-test, the following routing rules apply:

HTTP requests with the version:v1 header and the path /test will be routed to the v1 subset of spring-test on port 8003.

Other HTTP requests will be routed to the base subset of spring-test on port 8003.

DestinationRule:

apiVersion: networking.istio.io/v1alpha3
kind: DestinationRule
metadata:
  name: spring-test-destinationrule
spec:
  host: spring-test.default.svc.cluster.local
  subsets:
  - name: v1
    labels:
      version: v1
    trafficPolicy:
      loadBalancer:
        localityLbSetting:
          enabled: true
  subsets:
  - name: base
    labels:
      version: base
    trafficPolicy:
      loadBalancer:
        localityLbSetting:
          enabled: false

Description: The spring-test service is divided into two subsets based on the version label, representing two service clusters. The v1 cluster uses a same AZ routing strategy, while the base cluster does not.

In the future, the Sermant framework will implement routing configuration retrieval capabilities based on the xDS protocol, which will be used for service governance at the plugin layer.

# Sermant Plugins Supportting xDS Routing Service

Router Plugin

# Load Balancing based on xDS Service

The Sermant framework implements the ability to retrieve load balancing configurations based on the xDS protocol. Plugins can call the xDS load balancing configuration service interface to obtain load balancing configurations for Kubernetes Services. For specific development guidance, please refer to Development Guide for Load Balancing Configuration Service Basedon xDS.

# Supported Istio Load Balancing Configuration Fields

Istio delivers load balancing configurations via custom resource files such as DestinationRule. Sermant communicates with Istio's control plane using the xDS protocol to retrieve load balancing configurations. The following table lists the supported load balancing configuration fields and rules:

Supported Fields	Description
spec.trafficPolicy	Traffic policy
spec.trafficPolicy.loadBalancer	Load balancing strategy
spec.trafficPolicy.loadBalancer.simple	Simple load balancing strategies: supports ROUND_ROBIN, RANDOM, LEAST_REQUEST

# Istio Load Balancing Configuration Template

DestinationRule:

apiVersion: networking.istio.io/v1alpha3
kind: DestinationRule
metadata:
  name: spring-test-destinationrule
spec:
  host: spring-test.default.svc.cluster.local
  trafficPolicy:
    loadBalancer:
      simple: ROUND_ROBIN
  subsets:
  - name: v1
    labels:
      version: v1
    trafficPolicy:
      loadBalancer:
        simple: RANDOM
  subsets:
  - name: base
    labels:
      version: base

Description: The spring-test service is divided into two subsets based on the version label, representing two service clusters. The v1 cluster uses a RANDOM load balancing strategy, while the base cluster uses a ROUND-ROBIN load balancing strategy.

# Sermant Plugins Supporting xDS Load Balancing Service

Routing Plugin

# Startup and Result Verification

# Service Discovery Example Based on xDS Service

This tutorial demonstrates the xDS service discovery capabilities of Sermant using the Sermant-examples (opens new window) repository's xds-service-discovery-demo.

This demo includes a spring-client microservice, a spring-server microservice, and a Sermant example plugin. The plugin intercepts the hello method of the spring-client and uses Sermant's xDS service discovery capabilities to get specific instance information of the spring-server service before executing the hello method, replacing the input parameter with the correct spring-server address.

# 1 Preparations

Download (opens new window) the binary package of the demo.
Prepare the Kubernetes environment.
Install Istio and start it.

# 2 Obtaining the Demo Binary Package

Extract the binary package to get the product/ directory files.

# 3 Starting the spring-server

Enter the product/spring-server directory:

Execute the following command to package the spring-server image:
```
sh build-server.sh
```
Execute the following command to run the spring-server pod and service:
```
kubectl apply -f spring-server.yaml
```

# 4 Starting the spring-client

Enter the product/spring-client directory:

Execute the following command to package the spring-client image:
```
sh build-client.sh
```
Execute the following command to run the spring-client instance and service:
```
kubectl apply -f spring-client.yaml
```

# 5 Verification

Access the spring-client microservice via a web page, set the input parameter address to empty, and verify whether Sermant can successfully call the upstream service spring-server:

http://127.0.0.1:30110/hello?address=

The webpage shows the following message, indicating that Sermant successfully discovered the instance of spring-server and modified the address parameter to the correct spring-server instance address:

Greetings from http://xxx.xxx.xxx.xxx:8080 : hello, the current time is 2050-01-01T02:08:08.369

# Routing Example Based on xDS Service

This tutorial demonstrates Sermant's routing capabilities based on xDS service using the xds-router-demo from the Sermant-examples (opens new window) repository. The demo includes two microservices: spring-client and spring-server. The spring-client microservice starts with the Sermant routing plugin and enables xDS-based routing capabilities. When the spring-client calls upstream services, the Sermant routing plugin routes the requests based on the upstream service’s routing rules, selecting the appropriate service instance that meets the rules.

# 1. Preparation

Download (opens new window) the demo binary artifact package.
Download (opens new window) the Sermant binary artifact package.
Prepare a Kubernetes environment.
Install and start Istio (opens new window).

# 2. Obtain the Demo Binary Artifacts

Unzip the demo binary artifact package to get the router-product/ directory.

# 3. Obtain and Move the Sermant Binary Artifacts

Unzip the Sermant binary artifact package to get the sermant-agent/ directory.

Run the following command to move the Sermant binary artifacts to the spring-client directory for packaging the spring-client image:

cp -r ${sermant-path}/sermant-agent/agent ${demo-path}/router-product/spring-client

Note: ${sermant-path} is the path to the Sermant binary artifacts, and ${demo-path} is the path to the demo binary artifacts.

# 4. Start `spring-server`

Navigate to the router-product/spring-server directory:

Run the following command to package the spring-server image:
```
sh build-server.sh
```
Run the following command to deploy the spring-server Pod and Service:
```
kubectl apply -f ../script/spring-server.yaml
```

# 5. Start `spring-client`

Navigate to the product/spring-client directory:

Run the following command to package the spring-client image:
```
sh build-client.sh
```
Run the following command to deploy the spring-client Pod and Service:
```
kubectl apply -f ../script/spring-client.yaml
```

# 6. Apply Routing Rules

Navigate to the product/script directory and apply the routing rules by running the following commands:

kubectl apply -f spring-server-destination.yaml
kubectl apply -f spring-server-virtureservice.yaml

Routing Rules Explanation:

DestinationRule: Divides the Pods into two subsets, v1 and v2, based on the version label of the Deployment. The spring-server cluster uses the ROUND_ROBIN load balancing strategy.

VirtualService: Routes HTTP requests to the spring-server service to the v1 subset if the request contains the version:v1 header and the request path is /router.

# 7. Verification

Access the spring-client microservice via a web browser, set the host parameter to spring-server, and set versionto v1. Verify that the spring-client successfully calls the v1 version of the upstream spring-server service:

http://127.0.0.1:30110/router/httpClient?host=spring-server&version=v1

If the web page displays the following output, it indicates that spring-client successfully called the v1 version of the spring-server service:

spring-server version: v1

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# Proxyless Service Mesh Based on Sermant and Istio

# Service Governance of Sermant in Istio Environment

# Istio+Sermant Sidecar Proxyless Mode Deployment

# Advantages of using Sermant in Istio Environment

# Service Discovery based on xDS Service

# Template for Creating Pod and Service in Kubernetes

# Sermant Plugins Supportting xDS Service Discovery

# Routing based on xDS Service

# Supported Istio Routing Configuration Fields

# Istio Routing Configuration Template

# Sermant Plugins Supportting xDS Routing Service

# Load Balancing based on xDS Service

# Supported Istio Load Balancing Configuration Fields

# Istio Load Balancing Configuration Template

# Sermant Plugins Supporting xDS Load Balancing Service

# Startup and Result Verification

# Service Discovery Example Based on xDS Service

# 1 Preparations

# 2 Obtaining the Demo Binary Package

# 3 Starting the spring-server

# 4 Starting the spring-client

# 5 Verification

# Routing Example Based on xDS Service

# 1. Preparation

# 2. Obtain the Demo Binary Artifacts

# 3. Obtain and Move the Sermant Binary Artifacts

# 4. Start spring-server

# 5. Start spring-client

# 6. Apply Routing Rules

# 7. Verification

# 4. Start `spring-server`

# 5. Start `spring-client`