EC2 HTTP modify header

EC2 HTTP modify header injects HTTP chaos which affects the request (or response) by modifying the status code (or the body or the headers) by starting the proxy server and redirecting the traffic through the proxy server. This fault modifies the headers of requests and responses of the service.

Use cases

EC2 HTTP modify header tests the resilience of the application to incorrect or incomplete headers.

Prerequisites

• Kubernetes >= 1.17
• You can pass the VM credentials as secrets or as a ChaosEngine environment variable.
• The EC2 instance should be in a healthy state.
• SSM agent is installed and running in the target EC2 instance.
• The Kubernetes secret should have the AWS Access Key ID and Secret Access Key credentials in the CHAOS_NAMESPACE. A secret file looks like:

  apiVersion: v1
  kind: Secret
  metadata:
    name: cloud-secret
  type: Opaque
  stringData:
    cloud_config.yml: |-
      # Add the cloud AWS credentials respectively
      [default]
      aws_access_key_id = XXXXXXXXXXXXXXXXXXX
      aws_secret_access_key = XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

tip

HCE recommends that you use the same secret name, that is, cloud-secret. Otherwise, you will need to update the AWS_SHARED_CREDENTIALS_FILE environment variable in the fault template with the new secret name and you won't be able to use the default health check probes.

Below is an example AWS policy to execute the fault.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "ssm:GetDocument",
                "ssm:DescribeDocument",
                "ssm:GetParameter",
                "ssm:GetParameters",
                "ssm:SendCommand",
                "ssm:CancelCommand",
                "ssm:CreateDocument",
                "ssm:DeleteDocument",
                "ssm:GetCommandInvocation",          
                "ssm:UpdateInstanceInformation",
                "ssm:DescribeInstanceInformation"
            ],
            "Resource": "*"
        },
        {
            "Effect": "Allow",
            "Action": [
                "ec2messages:AcknowledgeMessage",
                "ec2messages:DeleteMessage",
                "ec2messages:FailMessage",
                "ec2messages:GetEndpoint",
                "ec2messages:GetMessages",
                "ec2messages:SendReply"
            ],
            "Resource": "*"
        },
        {
            "Effect": "Allow",
            "Action": [
                "ec2:DescribeInstanceStatus",
                "ec2:DescribeInstances"
            ],
            "Resource": [
                "*"
            ]
        }
    ]
}

note

• Go to AWS named profile for chaos to use a different profile for AWS faults and superset permission or policy to execute all AWS faults.
• Go to the common attributes to tune the common tunables for all the faults.

Mandatory tunables

Tunable	Description	Notes
EC2_INSTANCE_ID	ID of the target EC2 instance.	For example, i-044d3cb4b03b8af1f. For more information, go to EC2 instance ID.
REGION	The AWS region ID where the EC2 instance has been created.	For example, us-east-1.
TARGET_SERVICE_PORT	Port of the service to target.	Default: port 80. For more information, go to target service port.
HEADERS_MAP	Map of headers to modify (or add).	For example, {"X-Litmus-Test-Header":"X-Litmus-Test-Value"}. To remove a header, just set the value to ""; For example, {"X-Litmus-Test-Header": ""}. For more information, go to headers map.
HEADER_MODE	Whether to modify response headers or request headers. Accepted values: request, response.	Default: response. For more information, go to header mode.

Optional tunables

Tunable	Description	Notes
TOTAL_CHAOS_DURATION	Duration that you specify, through which chaos is injected into the target resource (in seconds).	Default: 30 s. For more information, go to duration of the chaos.
CHAOS_INTERVAL	Time interval between two successive instance terminations (in seconds).	Default: 30 s. For more information, go to chaos interval.
AWS_SHARED_CREDENTIALS_FILE	Provide the path for aws secret credentials.	Default: /tmp/cloud_config.yml.
SEQUENCE	It defines the sequence of chaos execution for multiple instances.	Default: parallel. Supports serial and parallel. For more information, go to sequence of chaos execution.
RAMP_TIME	Period to wait before and after injection of chaos (in seconds).	For example, 30 s. For more information, go to ramp time.
INSTALL_DEPENDENCY	Select to install dependencies used to run the network chaos. It can be either True or False.	If the dependency already exists, you can turn it off. Defaults to True.
PROXY_PORT	Port where the proxy will be listening for requests.	Default: 20000. For more information, go to proxy port.
TOXICITY	Percentage of HTTP requests to be affected.	Default: 100. For more information, go to toxicity.
NETWORK_INTERFACE	Network interface to be used for the proxy.	Default: eth0. For more information, go to network interface.

Target service port

Port of the target service. Tune it by using the TARGET_SERVICE_PORT environment variable.

The following YAML snippet illustrates the use of this environment variable:

## provide the port of the targeted service
apiVersion: litmuschaos.io/v1alpha1
kind: ChaosEngine
metadata:
  name: engine-nginx
spec:
  engineState: "active"
  chaosServiceAccount: litmus-admin
  experiments:
  - name: ec2-http-modify-header
    spec:
      components:
        env:
        # provide the port of the targeted service
        - name: TARGET_SERVICE_PORT
          value: "80"

Modifying the response headers

Body string to modify the response header. Tune it by using the HEADER_MAP environment variable. HEADER_MODE environment variable is used to choose between modifying the request or response headers.

tip

HTTP_CHAOS_TYPE should be provided as header.

The following YAML snippet illustrates the use of this environment variable:

## provide the headers as a map
apiVersion: litmuschaos.io/v1alpha1
kind: ChaosEngine
metadata:
  name: engine-nginx
spec:
  engineState: "active"
  chaosServiceAccount: litmus-admin
  experiments:
  - name: ec2-http-modify-header
    spec:
      components:
        env:
        # map of headers to modify/add; For example, {"X-Litmus-Test-Header": "X-Litmus-Test-Value"}
        # to remove a header, just set the value to ""; For example, {"X-Litmus-Test-Header": ""}
        - name: HEADERS_MAP
          value: '{"X-Litmus-Test-Header": "X-Litmus-Test-Value"}'
        # whether to modify response headers or request headers. Accepted values: request, response
        - name: HEADER_MODE
          value: 'response'
        # provide the port of the targeted service
        - name: TARGET_SERVICE_PORT
          value: "80"

Modifying the request headers

Body string to modify the request header. Tune it by using the HEADERS_MAP environment variable. HEADER_MODE environment variable is used to choose between modifying the request or response headers.

tip

HTTP_CHAOS_TYPE should be provided as header.

The following YAML snippet illustrates the use of this environment variable:

## provide the headers as a map
apiVersion: litmuschaos.io/v1alpha1
kind: ChaosEngine
metadata:
  name: engine-nginx
spec:
  engineState: "active"
  chaosServiceAccount: litmus-admin
  experiments:
  - name: ec2-http-modify-header
    spec:
      components:
        env:
        # map of headers to modify/add; For example, {"X-Litmus-Test-Header": "X-Litmus-Test-Value"}
        # to remove a header, just set the value to ""; For example, {"X-Litmus-Test-Header": ""}
        - name: HEADERS_MAP
          value: '{"X-Litmus-Test-Header": "X-Litmus-Test-Value"}'
        # whether to modify response headers or request headers. Accepted values: request, response
        - name: HEADER_MODE
          value: 'response'
        # provide the port of the targeted service
        - name: TARGET_SERVICE_PORT
          value: "80"

Proxy port

Port where the proxy server listens for requests. Tune it by using the PROXY_PORT environment variable.

The following YAML snippet illustrates the use of this environment variable:

# provide the port for proxy server
apiVersion: litmuschaos.io/v1alpha1
kind: ChaosEngine
metadata:
  name: engine-nginx
spec:
  engineState: "active"
  chaosServiceAccount: litmus-admin
  experiments:
  - name: ec2-http-modify-header
    spec:
      components:
        env:
        # provide the port for proxy server
        - name: PROXY_PORT
          value: '8080'
        # provide the port of the targeted service
        - name: TARGET_SERVICE_PORT
          value: "80"

Toxicity

Percentage of the total number of HTTP requests that are affected. Tune it by using the TOXICITY environment variable.

The following YAML snippet illustrates the use of this environment variable:

## provide the toxicity
apiVersion: litmuschaos.io/v1alpha1
kind: ChaosEngine
metadata:
  name: engine-nginx
spec:
  engineState: "active"
  chaosServiceAccount: litmus-admin
  experiments:
  - name: ec2-http-modify-header
    spec:
      components:
        env:
        # toxicity is the probability of the request that is affected
        # provide the percentage value in the range of 0-100
        # 0 means no request will be affected and 100 means all requests will be affected
        - name: TOXICITY
          value: "100"
        # provide the port of the targeted service
        - name: TARGET_SERVICE_PORT
          value: "80"

Network interface

Network interface used for the proxy. Tune it by using the NETWORK_INTERFACE environment variable.

The following YAML snippet illustrates the use of this environment variable:

## provide the network interface for proxy
apiVersion: litmuschaos.io/v1alpha1
kind: ChaosEngine
metadata:
  name: engine-nginx
spec:
  engineState: "active"
  chaosServiceAccount: litmus-admin
  experiments:
  - name: ec2-http-modify-header
    spec:
      components:
        env:
        # provide the network interface for proxy
        - name: NETWORK_INTERFACE
          value: "eth0"
        # provide the port of the targeted service
        - name: TARGET_SERVICE_PORT
          value: '80'