website/docs/simulate-jvm-application-chaos.md

title
Simulate JVM Application Faults

Chaos Mesh simulates the faults of JVM application through Byteman. The supported fault types are as follows:

• Throw custom exceptions
• Trigger garbage collection
• Increase method latency
• Modify return values of a method
• Trigger faults by setting Byteman configuration files
• Increase JVM pressure

This document describes how to use Chaos Mesh to create the above fault types of JVM experiments.

:::note

Your Linux kernel must be v4.1 or later.

:::

Create experiments using Chaos Dashboard

1. Open Chaos Dashboard, and click NEW EXPERIMENT on the page to create a new experiment.

   

2. In the Choose a Target area, choose JVM FAULT, and select a specific behavior, such as RETURN. Then, fill out the detailed configurations.

   

   For information about how to fill out the configurations, refer to [Field Description] (#field-description).

3. Fill out the experiment information, and specify the experiment scope and the scheduled experiment duration.

   

4. Submit the experiment information.

Create experiments using YAML files

The following example shows the usage and effects of JVMChaos. The example specifies the return values of a method. The YAML files referred to in the following steps can be found in examples/jvm. The default work directory for the following steps is also examples/jvm. The default namespace where Chaos Mesh is installed is chaos-mesh.

Step 1. Create the target application

Helloworld is a simple Java application. In this section, this application is used as the target application that is to be tested. The target application is defined in example/jvm/app.yaml as follows:

apiVersion: v1
kind: Pod
metadata:
  name: helloworld
  namespace: helloworld
spec:
  containers:
    - name: helloworld
      # source code: https://github.com/WangXiangUSTC/byteman-example/tree/main/example.helloworld
      # this application will print log like this below:
      # 0. Hello World
      # 1. Hello World
      # ...
      image: xiang13225080/helloworld:v1.0
      imagePullPolicy: IfNotPresent

1. Create the namespace for the target application:

   kubectl create namespace helloworld
   

2. Build the application Pod:

   kubectl apply -f app.yaml
   

3. Execute kubectl -n helloworld get pods, and you are expected to find a pod named helloworld in the helloworld namespace.

   kubectl -n helloworld get pods
   

   The result is as follows:

   kubectl get pods -n helloworld
   NAME         READY   STATUS    RESTARTS   AGE
   helloworld   1/1     Running   0          2m
   

   After the READY column turns to 1/1, you can proceed to the next step.

Step 2. Observe application behaviors before injecting faults​

You can observe the behavior of helloworld application before injecting faults, for example:

kubectl -n helloworld logs -f helloworld

The result is as follows:

0. Hello World
1. Hello World
2. Hello World
3. Hello World
4. Hello World
5. Hello World

You can see that helloworld outputs a line of Hello World every second, and the number of each line increases in turn.

Step 3. Inject JVMChaos and check

1. The JVMChaos with a specified return value is as follows:

   apiVersion: chaos-mesh.org/v1alpha1
   kind: JVMChaos
   metadata:
     name: return
     namespace: helloworld
   spec:
     action: return
     class: Main
     method: getnum
     value: '9999'
     mode: all
     selector:
       namespaces:
         - helloworld
   

   JVMChaos changes the return value of the getnum method to the number 9999, which means that the number of each line in the helloworld output is set to 9999.

2. Inject JVMChaos with a specified value:

   kubectl apply -f ./jvm-return-example.yaml
   

3. Check the latest log of helloworld:

   kubectl -n helloworld logs -f helloworld
   

   The log is as follows:

   Rule.execute called for return_0:0
   return execute
   caught ReturnException
   9999. Hello World
   

Field description

Parameter	Type	Description	Default value	Required	Example
action	string	Indicates the specific fault type. The available fault types include latency, return, exception, stress, gc, and ruleData.	None	Yes	return
mode	string	Indicates how to select Pod. The supported modes include one, all, fixed, fixed-percent, and random-max-percent.	None	Yes	one

The meanings of the different action values are as follows:

Value	Meaning
latency	Increase method latency
return	Modify return values of a method
exception	Throw custom exceptions
stress	Increase CPU usage of Java process, or cause memory overflow (support heap overflow and stack overflow)
gc	Trigger garbage collection
ruleData	Trigger faults by setting Byteman configuration files

For different action values, there are different configuration items that can be filled in.

Parameters for latency

Parameter	Type	Description	Required
class	string	The name of the Java class	Yes
method	string	The name of the method	Yes
latency	int	The duration of increasing method latency. The unit is millisecond.	Yes
port	int	The port ID attached to the Java process agent. The faults are injected into the Java process through this ID.	No

Parameters for return

Parameter	Type	Description	Required
class	string	The name of the Java class	Yes
method	string	The name of the method	Yes
value	string	Specifies the return value of the method. Currently, the item can be numeric and string types. If the item (return value) is string, double quotes are required, like "chaos".	Yes
port	int	The port ID attached to the Java process agent. The faults are injected into the Java process through this ID.	No

Parameters for exception

Parameter	Type	Description	Required
class	string	The name of the Java class	Yes
method	string	The name of the method	Yes
exception	string	The thrown custom exception, such as 'java.io.IOException("BOOM")'.	Yes
port	int	The port ID attached to the Java process agent. The faults are injected into the Java process through this ID.	No

Parameters for stress

Parameter	Type	Description	Required
cpuCount	int	The number of CPU cores used for increasing CPU stress. You must configure one item between cpu-count and mem-type.	No
memType	string	The type of OOM. Currently, both 'stack' and 'heap' OOM types are supported. You must configure one item between cpu-count and mem-type.	No
port	int	The port ID attached to the Java process agent. The faults are injected into the Java process through this ID.	No

Parameters for gc

Parameter	Type	Description	Required
port	int	The port ID attached to the Java process agent. The faults are injected into the Java process through this ID.	No

Parameters for ruleData

Parameter	Type	Description	Required
ruleData	string	Specifies the Byteman configuration data	Yes
port	int	The port ID attached to the Java process agent. The faults are injected into the Java process through this ID.	No

When you write the rule configuration file, take into account the specific Java program and the byteman-rule-language. For example:

RULE modify return value
CLASS Main
METHOD getnum
AT ENTRY
IF true
DO
    return 9999
ENDRULE

You need to escape the line breaks in the configuration file to the newline character "\n", and use the escaped text as the value of "rule-data" as follows:

\nRULE modify return value\nCLASS Main\nMETHOD getnum\nAT ENTRY\nIF true\nDO return 9999\nENDRULE\n"