# Sermant Agent User Manual

Sermant Agent is the core component providing bytecode enhancement capabilities and various service governance functionalities. The content under the sermant-agent-x.x.x/agent directory described in the Sermant Introduction outlines the modules of the Sermant Agent component. The main body of Sermant Agent offers foundational bytecode enhancement capabilities and a development framework, while also supporting essential features such as heartbeat functionality, dynamic configuration, logging, and event reporting. It currently supports both premain and agentmainstartup methods.

The Sermant Agent plugin directory includes plugins that provide service governance capabilities such as tag routing, rate limiting and degradation, and dual registration. It now supports the dynamic installation and uninstallation of service governance plugins while the host service is running, provided the plugins support dynamic installation and uninstallation.

# Supported Version

Sermant Agent supports Linux and Windows, and is developed based on JDK 1.8. It is recommended to use JDK 1.8 or higher versions.

HuaweiJDK 1.8 (opens new window) / OpenJDK 1.8 (opens new window) / OracleJDK 1.8 (opens new window)

# Premain Startup: Static Attachment

To start Sermant Agent using the premain method via static attachment, configure the host service with the -javaagentoption. Based on the environment set up in the Quick Start Guide, execute the following command to launch Sermant Agent:

# linux mac
java -javaagent:${path}/sermant-agent-x.x.x/agent/sermant-agent.jar -jar spring-provider.jar

# windows
java -javaagent:${path}\sermant-agent-x.x.x\agent\sermant-agent.jar -jar spring-provider.jar

Check the beginning of the spring-provider.jar log to see if it contains the following content:

[xxxx-xx-xxTxx:xx:xx.xxx] [INFO] Loading god library into BootstrapClassLoader.
[xxxx-xx-xxTxx:xx:xx.xxx] [INFO] Building argument map by agent arguments.
[xxxx-xx-xxTxx:xx:xx.xxx] [INFO] Loading core library into SermantClassLoader.
[xxxx-xx-xxTxx:xx:xx.xxx] [INFO] Loading sermant agent, artifact is: default
[xxxx-xx-xxTxx:xx:xx.xxx] [INFO] Load sermant done, artifact is: default

If the log outputs as shown above, it indicates that Sermant Agent has started successfully. Open your browser and navigate to http://localhost:8900, where you should see a Sermant Agent instance. The expected result is shown in the image below:

# Agentmain Startup：Dynamic Attachment

# Agent Installation

Based on the environment set up in the Quick Start Guide, first start the host service spring-provider.jar.

java -jar spring-provider.jar

To start by agentmain, you need to use the Attach API. First, create a Java file using the AgentLoader.java and compile it with javac:

# Linux、MacOS
javac -cp ./:$JAVA_HOME/lib/tools.jar AgentLoader.java

# Windows has correctly configured the environment variables required for JAVA.
javac -cp "%JAVA_HOME%\lib\tools.jar" AgentLoader.java -encoding utf-8

After compilation, an AgentLoader.class file will be generated in the directory. Run AgentLoader using the following command:

# Linux、MacOS
java -cp ./:$JAVA_HOME/lib/tools.jar AgentLoader

# Windows has correctly configured the environment variables required for JAVA.
java AgentLoader

# Choose the command to run based on the operating system you are using. Below are the commands for Linux and MacOS:
$ java -cp ./:$JAVA_HOME/lib/tools.jar AgentLoader
Please select the Java process you wish to use with Sermant Agent:
0: xxxxx AgentLoader # xxxxx represents the process ID, which is obscured here.
1: xxxxx spring-provider.jar # xxxxx represents the process ID, which is obscured here.
2: xxxxx sermant-backend-1.2.0.jar # xxxxx represents the process ID, which is obscured here.
Please enter the Java process number you wish to use with Sermant Agent: 1 # Select the process number of spring-provider.
The process ID you selected: xxxxx # xxxxx represents the process ID, which is obscured here.
Please enter the directory where Sermant Agent is located (by default, it uses sermant-agent.jar in this directory as the entry point): ${path}/sermant-agent-x.x.x/agent # Enter the directory where Sermant Agent is located.
Please enter the parameters to pass to Sermant Agent (can be empty, default configuration parameter is agentPath): # Configure Sermant Agent parameters (can be empty)

After completing the input according to the instructions, you can see the following content in the spring-provider.jarlog:

[xxxx-xx-xxTxx:xx:xx.xxx] [INFO] Loading god library into BootstrapClassLoader.
[xxxx-xx-xxTxx:xx:xx.xxx] [INFO] Building argument map by agent arguments.
[xxxx-xx-xxTxx:xx:xx.xxx] [INFO] Loading core library into SermantClassLoader.
[xxxx-xx-xxTxx:xx:xx.xxx] [INFO] Loading sermant agent, artifact is: default
[xxxx-xx-xxTxx:xx:xx.xxx] [INFO] Load sermant done, artifact is: default

If the log outputs as shown above, it indicates that Sermant Agent successfully read the startup command and began the installation. Open your browser and navigate to http://localhost:8900, where you should see a Sermant Agent instance. The expected result is shown in the image below:

# Agent Uninstallation

Note: To avoid potential unpredictable exceptions when uninstalling service governance capabilities developed based on the premain startup method, Sermant Agent imposes restrictions on uninstallation. Only Sermant Agents started via the agentmain method support uninstallation; those started via the premain method do not support uninstallation.

After dynamically attaching the Agent, you can uninstall Agent. Run AgentLoader again and pass the parameter to issue the uninstall command for Sermant Agent using command=UNINSTALL-AGENT:

# Choose the command to run based on the operating system you are using. Below are the commands for Linux and MacOS:
$ java -cp ./:$JAVA_HOME/lib/tools.jar AgentLoader
Please select the Java process you wish to use with Sermant Agent:
0: xxxxx AgentLoader # xxxxx represents the process ID, which is obscured here.
1: xxxxx spring-provider.jar # xxxxx represents the process ID, which is obscured here.
2: xxxxx sermant-backend-1.2.0.jar # xxxxx represents the process ID, which is obscured here.
Please enter the Java process number you wish to use with Sermant Agent: 1 # Select the process number of spring-provider.
The process ID you selected: xxxxx # xxxxx represents the process ID, which is obscured here.
Please enter the directory where Sermant Agent is located (by default, it uses sermant-agent.jar in this directory as the entry point): ${path}/sermant-agent-x.x.x/agent # Enter the directory where Sermant Agent is located.
Please enter the parameters to pass to Sermant Agent (can be empty, default configuration parameter is agentPath):command=UNINSTALL-AGENT # Pass the parameter here to issue the uninstall command.

After completing the input according to the instructions, you can see the following content in the spring-provider.jarlog:

[xxxx-xx-xxTxx:xx:xx.xxx] [INFO] Building argument map by agent arguments.
[xxxx-xx-xxTxx:xx:xx.xxx] [INFO] Sermant for artifact is running, artifact is: default
[xxxx-xx-xxTxx:xx:xx.xxx] [INFO] Execute command: UNINSTALL-AGENT

If the log outputs as shown above, open your browser and navigate to http://localhost:8900. You should see that the Sermant Agent instance has been shut down (status is gray), indicating that Sermant Agent has been successfully uninstalled. The expected result is shown in the image below:

Note: This capability can be implemented in the development mode by calling the uninstall interface provided by AgentCoreEntrance (opens new window) in the sermant-agentcore-core module.

# Dynamic Plugin Installation

After dynamically attaching the Agent, you can dynamically install service governance plugins (provided the plugins support dynamic installation and uninstallation). Run AgentLoader again and pass the parameter to issue the dynamic plugin installation command using command=INSTALL-PLUGINS:pluginA/pluginB:

Note: Multiple plugins can be installed at once, separated by '/'. pluginA and pluginB are placeholders for actual plugin names. In this example, we use the monitor plugin.

# Choose the command to run based on the operating system you are using. Below are the commands for Linux and MacOS:
$ java -cp ./:$JAVA_HOME/lib/tools.jar AgentLoader
Please select the Java process you wish to use with Sermant Agent:
0: xxxxx AgentLoader # xxxxx represents the process ID, which is obscured here.
1: xxxxx spring-provider.jar # xxxxx represents the process ID, which is obscured here.
2: xxxxx sermant-backend-1.2.0.jar # xxxxx represents the process ID, which is obscured here.
Please enter the Java process number you wish to use with Sermant Agent: 1 # Select the process number of spring-provider.
The process ID you selected: xxxxx # xxxxx represents the process ID, which is obscured here.
Please enter the directory where Sermant Agent is located (by default, it uses sermant-agent.jar in this directory as the entry point): ${path}/sermant-agent-x.x.x/agent # Enter the directory where Sermant Agent is located.
Please enter the parameters to pass to Sermant Agent (can be empty, default configuration parameter is agentPath):command=INSTALL-PLUGINS:monitor # Pass the parameter here to issue the install plugin command. This example demonstrates using the monitor plugin.

After completing the input according to the instructions, you can see the following content in the spring-provider.jarlog:

[xxxx-xx-xxTxx:xx:xx.xxx] [INFO] Building argument map by agent arguments.
[xxxx-xx-xxTxx:xx:xx.xxx] [INFO] Sermant for artifact is running, artifact is: default
[xxxx-xx-xxTxx:xx:xx.xxx] [INFO] Execute command: INSTALL-PLUGINS:monitor # This example demonstrates using the monitor plugin.

If the log outputs as shown above, it indicates that the plugin was installed successfully. Open your browser and navigate to http://localhost:8900, where you should see that the plugin has been successfully installed. The plugins list will display the currently installed plugins, as shown in the image below:

Before dynamically installing plugin

After dynamically installing plugin

Note: This capability can be implemented in the development mode by calling the install(Set pluginNames) method provided by PluginManager (opens new window) in the sermant-agentcore-core module.

# Repeated Plugin Installation

The introduction of this capability is mainly due to the need for dynamically extending the effective scope of plugins in certain scenarios, primarily expanding the enhanced classes and methods, while ensuring that the already effective parts remain unaffected. In such cases, uninstalling and reinstalling plugins after adjusting configurations cannot address the issue.For example, in fault injection scenarios, different faults may require bytecode enhancement for different classes, and various fault scenarios need to be gradually injected according to the test plan's orchestration. In such cases, we cannot complete this task by uninstalling and reinstalling the plugin. Instead, we must install the fault injection plugin multiple times to solve this problem. This requires the capability of repeated plugin installation. Repeated plugin installation will reuse static resources, and Sermant internally isolates the repeatedly installed plugins through plugin management.

# How to Implement Repeated Plugin Installation?

To install plugins repeatedly, you need to add a unique identifier to the plugin name using the # symbol when performing dynamic plugin installation. For example:

command=INSTALL-PLUGINS:pluginA#FIRST

In this way, the plugin can be installed repeatedly.

Note: When uninstalling a plugin, if you want to uninstall a plugin that was installed with an identifier, you need to specify the plugin name with the identifier in the uninstall command as well.

# Dynamic Plugin Uninstallation

After dynamically attaching the Agent and dynamically installing the plugin, you can dynamically uninstall service governance plugins (provided the plugins support dynamic installation and uninstallation). Run AgentLoader again and pass the parameter to issue the dynamic plugin uninstallation command using command=UNINSTALL-PLUGINS:pluginA/pluginB:

Note: Multiple plugins can be uninstalled at once, separated by '/'. pluginA and pluginB are placeholders for actual plugin names. In this example, we use the monitor plugin.

# Choose the command to run based on the operating system you are using. Below are the commands for Linux and MacOS:
$ java -cp ./:$JAVA_HOME/lib/tools.jar AgentLoader
Please select the Java process you wish to use with Sermant Agent:
0: xxxxx AgentLoader # xxxxx represents the process ID, which is obscured here.
1: xxxxx spring-provider.jar # xxxxx represents the process ID, which is obscured here.
2: xxxxx sermant-backend-1.2.0.jar # xxxxx represents the process ID, which is obscured here.
Please enter the Java process number you wish to use with Sermant Agent: 1 # Select the process number of spring-provider.
The process ID you selected: xxxxx # xxxxx represents the process ID, which is obscured here.
Please enter the directory where Sermant Agent is located (by default, it uses sermant-agent.jar in this directory as the entry point): ${path}/sermant-agent-x.x.x/agent # Enter the directory where Sermant Agent is located.
Please enter the parameters to pass to Sermant Agent (can be empty, default configuration parameter is agentPath):command=UNINSTALL-PLUGINS:monitor # Pass the parameter here to issue the uninstall plugin command.

After completing the input according to the instructions, you can see the following content in the spring-provider.jarlog:

[xxxx-xx-xxTxx:xx:xx.xxx] [INFO] Building argument map by agent arguments.
[xxxx-xx-xxTxx:xx:xx.xxx] [INFO] Sermant for artifact is running, artifact is: default
[xxxx-xx-xxTxx:xx:xx.xxx] [INFO] Execute command: UNINSTALL-PLUGINS:monitor #This example demonstrates using "monitor" plugin.
# The log will show how many bytecode-enhanced classes were restored during the uninstallation.
[Byte Buddy] REDEFINE BATCH #0 [1 of 1 type(s)]
[Byte Buddy] REDEFINE COMPLETE 1 batch(es) containing 1 types [0 failed batch(es)]
[Byte Buddy] REDEFINE COMPLETE 1 batch(es) containing 0 types [0 failed batch(es)]

If the log outputs as shown above, open your browser and navigate to http://localhost:8900. You should see that the plugin has been successfully uninstalled. The plugins list will display the currently installed plugins, as shown in the image below:

Before dynamically installing plugin

After dynamically installing plugin

Note: This capability can be implemented in development mode by calling the uninstall(Set pluginNames) method provided by PluginManager (opens new window) in the sermant-agentcore-core module.

# One-Click Agent and Plugin Attachment

The Sermant Dynamic Installation and Uninstallation Script (opens new window) is a C language script based on the Java Attach API. It can attach Sermant Agent to JVM processes on either virtual machines or containers.

Note: This script is only for use on Linux systems.

# Parameter Configuration

-path=：required parameter, followed by the absolute path of sermant-agent.jar.
-pid=：required parameter, followed by the PID of the host microservice, which can be found using commands like ps -ef.
-command=：required parameter, followed by the command to attach Sermant Agent. Supported commands can be found in the Sermant Command Instructions.
-nspid=：when the host microservice is running in a container, this parameter is required and should be followed by the host microservice's nspid, which can be found using the cat /proc/{pid}/status command. If the host microservice is not running in a container, do not include this parameter.

# Script Usage Steps

# Step 1. Compile `jvm_attach.c`

gcc attach.c -o attach

Note: Please ensure that gcc is already installed.

# Step 2. Execute the Attach Script

./attach -path={sermant-path}/sermant-agent.jar -pid={pid} -command={COMMAND}

The script execution will display as follows:

[root@b6b9af8e5610 root]# ./attach -path=/home/sermant-agent-1.0.0/agent/sermant-agent.jar -pid=494 -command=INSTALL-PLUGINS:database-write-prohibition
[INFO]: PATH: /home/sermant-agent-1.0.0/agent/sermant-agent.jar
[INFO]: PID: 494
[INFO]: COMMAND: INSTALL-PLUGINS:database-write-prohibition
[INFO]: Connected to remote JVM of pid 494
[INFO]: ret code is 0, Attach success!

# Enhancement Information Query

After Sermant has been successfully started by any method, you can run AgentLoader and pass the parameter to issue the query enhancement information command using command=CHECK_ENHANCEMENT:

Note: The enhancement information query will be printed to the log at the INFO level. If you use this feature, please configure the log level in advance. For modification instructions, see Log Configuration

# Choose the command to run based on the operating system you are using. Below are the commands for Linux and MacOS:
$ java -cp ./:$JAVA_HOME/lib/tools.jar AgentLoader
Please select the Java process you wish to use with Sermant Agent:
0: xxxxx AgentLoader # xxxxx represents the process ID, which is obscured here.
1: xxxxx spring-provider.jar # xxxxx represents the process ID, which is obscured here.
2: xxxxx sermant-backend-1.2.0.jar # xxxxx represents the process ID, which is obscured here.
Please enter the Java process number you wish to use with Sermant Agent: 1 # Select the process number of spring-provider.
The process ID you selected: xxxxx # xxxxx represents the process ID, which is obscured here.
Please enter the directory where Sermant Agent is located (by default, it uses sermant-agent.jar in this directory as the entry point): ${path}/sermant-agent-x.x.x/agent # Enter the directory where Sermant Agent is located.
Please enter the parameters to pass to Sermant Agent (can be empty, default configuration parameter is agentPath):command=CHECK_ENHANCEMENT # Pass the parameter here to issue the query enhancement information command.

After completing the input according to the instructions, you can see the following content in the Sermant log:

xxxx-xx-xx xx:xx:xx.xxx [INFO] [io.sermant.core.command.CheckEnhancementsCommandExecutor] [execute:42] [Attach Listener] ---------- PLUGINS ----------
xxxx-xx-xx xx:xx:xx.xxx [INFO] [io.sermant.core.command.CheckEnhancementsCommandExecutor] [execute:44] [Attach Listener] test-plugin-A:1.0.0
xxxx-xx-xx xx:xx:xx.xxx [INFO] [io.sermant.core.command.CheckEnhancementsCommandExecutor] [execute:44] [Attach Listener] test-plugin-B:1.0.0
xxxx-xx-xx xx:xx:xx.xxx [INFO] [io.sermant.core.command.CheckEnhancementsCommandExecutor] [execute:46] [Attach Listener] ---------- ENHANCEMENT ----------
xxxx-xx-xx xx:xx:xx.xxx [INFO] [io.sermant.core.command.CheckEnhancementsCommandExecutor] [execute:58] [Attach Listener] test-plugin-A:1.0.0
xxxx-xx-xx xx:xx:xx.xxx [INFO] [io.sermant.core.command.CheckEnhancementsCommandExecutor] [execute:65] [Attach Listener] xxxxx.xxxx.TestClassA#testFunctionA(boolean,java.lang.String,java.lang.String,java.lang.String)@sun.misc.Launcher$AppClassLoader@5c647e05 [xxxx.xxxx.TestInterceptorA]
xxxx-xx-xx xx:xx:xx.xxx [INFO] [io.sermant.core.command.CheckEnhancementsCommandExecutor] [execute:65] [Attach Listener] xxxxx.xxxx.TestClassB#testFunctionB(boolean,java.lang.String,java.lang.String,java.lang.String)@sun.misc.Launcher$AppClassLoader@5c647e05 [xxxx.xxxx.TestInterceptorB,xxxx.xxxx.TestInterceptorC]

The format of the printed content is as follows:

---------- PLUGINS ----------
\\ List of installed plugins, formatted as: PluginName: PluginVersion
test-plugin-A:1.0.0
test-plugin-B:1.0.0
---------- ENHANCEMENT ----------
\\ Plugins that successfully completed enhancement processing, formatted as: PluginName: PluginVersion
test-plugin-A:1.0.0
\\ Information on plugins that successfully completed enhancement processing:
\\ Formatted as: EnhancedFullQualifiedClassName#EnhancedMethodName(ParameterType)@ClassLoaderInformation [InterceptorList]
xxxxx.xxxx.TestClassA#testFunctionA(boolean,java.lang.String,java.lang.String,java.lang.String)@sun.misc.Launcher$AppClassLoader@5c647e05 [xxxx.xxxx.TestInterceptorA]
xxxxx.xxxx.TestClassB#testFunctionB(boolean,java.lang.String,java.lang.String,java.lang.String)@sun.misc.Launcher$AppClassLoader@5c647e05 [xxxx.xxxx.TestInterceptorB,xxxx.xxxx.TestInterceptorC]

# Sermant Command Instructions

Sermant can achieve hot-plugging capabilities by running AgentLoader and passing in the following commands. Additionally, after Sermant Agent has been successfully started by any method, you can run AgentLoader and pass in commands to query enhancement information. The specific commands are as follows:

Command Type	Command Example
Agent Installation	If the command is empty, it defaults to Agent installation.
Agent Uninstallation	command=UNINSTALL-AGENT
Plugin Installation	command=INSTALL-PLUGINS:${PluginName}
Plugin Uninstallation	command=UNINSTALL-PLUGINS:${PluginName}
Repeated Plugin Installation	command=INSTALL-PLUGINS:${PluginName}#${CustomPluginIdentifier}
Enhancement Information Query	command=CHECK_ENHANCEMENT

# Sermant Core Services

# Dynamic Configuration Service

The Sermant Dynamic Configuration Service allows Sermant to pull configurations from the dynamic configuration center, enabling rich service governance capabilities. For a detailed introduction and usage of the Sermant Dynamic Configuration Service, please refer to the Dynamic Configuration Center User Manual.

# xDS Service

The Sermant xDS Service enables microservices to connect to Istio in Kubernetes scenarios. Sermant communicates directly with the Istio control plane based on the xDS protocol to retrieve configuration information for service discovery, routing, load balancing, and more, thereby replacing Envoy as the data plane for service governance capabilities in Istio. For a detailed introduction and usage of the Sermant xDS Service, please refer to Proxyless Service Mesh Based onSermant + Istio.

# Metric Service

The Sermant Metric Service allows users to collect and display core metrics and custom metrics from Sermant using monitoring tools like Prometheus. Through these metrics, users can gain real-time insights into the health of services and promptly identify potential issues.

# Prerequisites

Before using the Sermant Metric Service, ensure that the following conditions are met:

Sermant is correctly integrated into the application.
The Prometheus monitoring tool is installed and running.

# Configuring the Sermant Metric Service

# Enabling the Metric Service

Open the Sermant configuration file located at agent/config/config.properties.

Set the following configuration items to enable the Metric Service:

# Enable HTTP service
agent.service.httpserver.enable=true
# Enable Metric service
agent.service.metric.enable=true

# Configuring Prometheus

Open the Prometheus configuration file prometheus.yml.

Add the following configuration to scrape the metrics endpoint exposed by Sermant:

scrape_configs:
- job_name: 'sermant-metrics'
    metrics_path: '/sermant/metrics'
    static_configs:
    - targets: ['<Sermant-Host>:47128']

Replace <Sermant-Host> with the actual host address where Sermant is running.

# Using the Sermant Metric Service

# Creating Custom Metrics

If you need to create custom metrics in your plugin, please refer to: Metric Function.

# Viewing Metrics

Start the Prometheus service.
Access the Prometheus web interface, typically at http://<Prometheus-Host>:9090.
In the Prometheus query interface, enter the metric name, such as custom_counter_total, to view the corresponding metric data.

# Configuration Specifications

The properties configuration files of the Sermant project and the YAML configuration files of each plugin support the following parameter configuration methods. For example, in the configuration file, gateway.nettyIp=127.0.0.1:

Directly modify the configuration file by changing gateway.nettyIp=127.0.0.1 in the file.
Configure it via the -D parameter when starting the microservice, i.e., -Dgateway.nettyIp=127.0.0.1.
Configure it via an environment variable by adding gateway.nettyIp=127.0.0.1 to the environment variables.
Configure it via Sermant Agent startup parameters, i.e., -javaagent:sermant-agent.jar=gateway.nettyIp=127.0.0.1.

The four methods listed above, arranged in order of priority from highest to lowest, are: 4 > 3 > 2 > 1.

Among these, the values for the last three parameter configuration methods support multiple formats. For example, for gateway.nettyIp=127.0.0.1 in the configuration file, the following formats are all recognizable:

gateway.nettyIp=127.0.0.1
gateway_nettyIp=127.0.0.1
gateway-nettyIp=127.0.0.1
GATEWAY.NETTYIP=127.0.0.1
GATEWAY_NETTYIP=127.0.0.1
GATEWAY-NETTYIP=127.0.0.1
gateway.nettyip=127.0.0.1
gateway_nettyip=127.0.0.1
gateway-nettyip=127.0.0.1
gateway.netty.ip=127.0.0.1
gateway_netty_ip=127.0.0.1
gateway-netty-ip=127.0.0.1
GATEWAY.NETTY.IP=127.0.0.1
GATEWAY_NETTY_IP=127.0.0.1
GATEWAY-NETTY-IP=127.0.0.1

The Sermant Agent will sequentially check each configuration value from top to bottom to see if it is configured via startup parameters, environment variables, or -D parameters.

Note: When modifying configurations through container scenarios using env, replace point (.) with underscore (_).

Reason: Some OS images cannot recognize env variables with point.

For example：To modify the configuration gateway.nettyIp=127.0.0.1 through the pod's env, use:

  env:
  - name: "gateway_nettyIp"
    value: "127.0.0.2"

# Attachments

# AgentLoader.java

import com.sun.tools.attach.AgentInitializationException;
import com.sun.tools.attach.AgentLoadException;
import com.sun.tools.attach.AttachNotSupportedException;
import com.sun.tools.attach.VirtualMachine;
import com.sun.tools.attach.VirtualMachineDescriptor;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.List;

public class AgentLoader {
    private AgentLoader() {
    }

    /**
     * AgentLoader main method
     */
    public static void main(String[] args)
        throws IOException, AttachNotSupportedException, AgentLoadException, AgentInitializationException {
        List<VirtualMachineDescriptor> vmDescriptors = VirtualMachine.list();

        if (vmDescriptors.isEmpty()) {
            System.out.println("not find Java process");
            return;
        }

        System.out.println("Please select the Java process you wish to use with Sermant Agent: ");
        for (int i = 0; i < vmDescriptors.size(); i++) {
            VirtualMachineDescriptor descriptor = vmDescriptors.get(i);
            System.out.println(i + ": " + descriptor.id() + " " + descriptor.displayName());
        }

        // Read the user-inputted number
        BufferedReader userInputReader = new BufferedReader(new InputStreamReader(System.in));
        System.out.print("Please enter the Java process number you wish to use with Sermant Agent: ");
        int selectedProcessIndex = Integer.parseInt(userInputReader.readLine());

        if (selectedProcessIndex < 0 || selectedProcessIndex >= vmDescriptors.size()) {
            System.out.println("Invalid process ID");
            return;
        }

        // Connect to the selected virtual machine
        VirtualMachineDescriptor selectedDescriptor = vmDescriptors.get(selectedProcessIndex);
        System.out.println("The process ID you selected: " + selectedDescriptor.id());

        VirtualMachine vm = VirtualMachine.attach(selectedDescriptor);

        // Get the Sermant Agent directory
        System.out.print("Please enter the directory where Sermant Agent is located (by default, it uses sermant-agent.jar in this directory as the entry point): ");
        String agentPath = userInputReader.readLine();

        // Get the parameters passed to the Sermant Agent
        System.out.print("Please enter the parameters to pass to Sermant Agent (can be empty, default configuration parameter is agentPath):");
        String agentArgs = "agentPath=" + agentPath + "," + userInputReader.readLine();

        // Close resource
        userInputReader.close();

        // Start Sermant Agent
        vm.loadAgent(agentPath + "/sermant-agent.jar", agentArgs);
        vm.detach();
    }
}

← Introduction to the use of Sermant Sermant Backend User Manual →

# Sermant Agent User Manual

# Supported Version

# Premain Startup: Static Attachment

# Agentmain Startup：Dynamic Attachment

# Agent Installation

# Agent Uninstallation

# Dynamic Plugin Installation

# Repeated Plugin Installation

# How to Implement Repeated Plugin Installation?

# Dynamic Plugin Uninstallation

# One-Click Agent and Plugin Attachment

# Parameter Configuration

# Script Usage Steps

# Step 1. Compile jvm_attach.c

# Step 2. Execute the Attach Script

# Enhancement Information Query

# Sermant Command Instructions

# Sermant Core Services

# Dynamic Configuration Service

# xDS Service

# Metric Service

# Prerequisites

# Configuring the Sermant Metric Service

# Enabling the Metric Service

# Configuring Prometheus

# Using the Sermant Metric Service

# Creating Custom Metrics

# Viewing Metrics

# Configuration Specifications

# Attachments

# AgentLoader.java

# Step 1. Compile `jvm_attach.c`