Skip to main content

AZ blackhole

Last updated on

AZ blackhole is an AWS fault that causes network blackhole by isolating traffic in specific availability zones across an entire region. You can control the blast radius by providing targeted VPC IDs for the AZ failure. This fault helps evaluates how well your applications and services handle the loss of network connectivity across the availability zone ensuring that failover mechanisms and redundancy strategies function as expected.

AZ Blackhole

Use cases​

AZ blackhole:

  • Checks how the applications and services handle the loss of network connectivity in specific zones.
  • Determines the effects of network isolation on critical business processes by simulating major network disruptions, helping teams to identify weak links and improve overall system robustness.
  • Tests and refine disaster recovery plans by simulating AZ-level blackholes, ensuring that your infrastructure can efficiently reroute traffic and maintain operational continuity during large-scale outages.

Prerequisites​

  • Kubernetes >= 1.17
  • Ensure you have the required AWS permissions to induce a network blackhole in the specified availability zone within the region..
  • Ensure that the specified VPC (if provided) includes the target availability zone.
  • The Kubernetes secret should have AWS access configuration (key) in the CHAOS_NAMESPACE. Below is a sample secret file. 
    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 = XXXXXXXXXXXXXXX
tip

Harness CE 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": [
        "ec2:DescribeVpcs",
        "ec2:DescribeSubnets",
        "ec2:DescribeNetworkAcls",
        "ec2:CreateNetworkAcl",
        "ec2:ReplaceNetworkAclAssociation",
        "ec2:DeleteNetworkAcl",
        "ec2:CreateNetworkAclEntry",
        "ec2:ModifyNetworkAclEntry"
      ],
      "Resource": "*"
    },
    {
      "Effect": "Allow",
      "Action": [
        "ec2:DescribeInstances",
        "ec2:DescribeSecurityGroups",
        "ec2:DescribeNetworkInterfaces",
        "ec2:DescribeAvailabilityZones"
      ],
      "Resource": "*"
    }
  ]
}

note

Mandatory Tunables​

Tunable Description Notes
REGION Region name for the target volumes. For example, us-east-1.

Optional Tunables​

Tunable Description Notes
TOTAL_CHAOS_DURATION Duration to insert chaos (in seconds). Default: 30 s. For more information, go to duration of the chaos.
AVAILABILITY_ZONES Provide the target availability zones to cause the network blackhole. For example, us-east-1a. For more information, go to availability zones.
VPC_IDS Provide the VPC IDs to limit the impact, ensuring the AZ blackhole targets only those specific networks. For example: "vpc-89765,vpc-78687". For more information, go to vpc ids.
SUBNET_IDS Provide the subnet IDs to further limit the blast radius to specific subnets within the target VPCs. For example: "subnet-0a1b2c3d,subnet-9z8y7x6w". For more information, go to subnet ids.
SUBNET_TAGS Provide the subnet tags to target specific subnets by their tag key-value pairs. For example: "env:production,team:backend". For more information, go to subnet tags.
AWS_SHARED_CREDENTIALS_FILE Path to the AWS secret credentials. Default: /tmp/cloud_config.yml.
CHAOS_INTERVAL Duration between the attachment and detachment of the volumes (in seconds). Default: 30 s. For more information, go to chaos interval.
SEQUENCE Sequence of chaos execution for multiple volumes. Default: parallel. Supports serial and parallel. For more information, go to sequence of chaos execution.
RAMP_TIME Period to wait before and after injecting chaos (in seconds). For example, 30 s. For more information, go to ramp time.

Use Case Description​

  1. If a user provides only the region parameter, then by default Harness selects all the VPCs in that region and the blast radius is maximum.
  2. If a user wants to control the blast radius, the options are:
    • Region with VPC ID: Targets specific VPCs within the region.
    • Region with VPC ID and Availability Zone: Targets specific availability zones within the specified VPCs.
    • Region with VPC ID, AZ, and Subnet Tag: Targets subnets matching the specified tags within the given VPCs and availability zones.
    • Region with VPC ID, AZ, and Subnet ID: Targets specific subnets by their IDs within the given VPCs and availability zones.

Availability Zones​

Comma-separated list of the target availability zones under blackhole attach. Tune it by using the AVAILABILITY_ZONES environment variable.

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

# contains az blackhole for given az
apiVersion: litmuschaos.io/v1alpha1
kind: ChaosEngine
metadata:
  name: engine-nginx
spec:
  engineState: "active"
  chaosServiceAccount: litmus-admin
  experiments:
  - name: az-blackhole
    spec:
      components:
        env:
        # target availability zones for the chaos
        - name: AVAILABILITY_ZONES
          value: 'us-east-1a,us-east-1b'
        # region for chaos
        - name: REGION
          value: 'us-east-1'

VPC IDS​

Comma-separated list of the VPC IDs to limit the impact. Tune it by using the VPC_IDS environment variable.

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

# contains vpc ids for given az
apiVersion: litmuschaos.io/v1alpha1
kind: ChaosEngine
metadata:
  name: engine-nginx
spec:
  engineState: "active"
  chaosServiceAccount: litmus-admin
  experiments:
  - name: az-blackhole
    spec:
      components:
        env:
        # target vpc ids for the chaos
        - name: VPC_IDS
          value: 'vpc-21312481928410,vpc-78926378028471'
        # target availability zones for the chaos
        - name: AVAILABILITY_ZONES
          value: 'us-east-1a,us-east-1b'
        # region for chaos
        - name: REGION
          value: 'us-east-1'

Subnet IDs​

Comma-separated list of the subnet IDs to further limit the blast radius to specific subnets. Tune it by using the SUBNET_IDS environment variable.

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

# contains subnet ids for given az
apiVersion: litmuschaos.io/v1alpha1
kind: ChaosEngine
metadata:
  name: engine-nginx
spec:
  engineState: "active"
  chaosServiceAccount: litmus-admin
  experiments:
  - name: az-blackhole
    spec:
      components:
        env:
        # target subnet ids for the chaos
        - name: SUBNET_IDS
          value: 'subnet-0a1b2c3d4e5f,subnet-9z8y7x6w5v4u'
        # target availability zones for the chaos
        - name: AVAILABILITY_ZONES
          value: 'us-east-1a,us-east-1b'
        # target vpc ids for the chaos
        - name: VPC_IDS
          value: 'vpc-21312481928410'
        # region for chaos
        - name: REGION
          value: 'us-east-1'

Subnet Tags​

Comma-separated list of the subnet tags (in key:value format) to target specific subnets. Tune it by using the SUBNET_TAGS environment variable.

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

# contains subnet tags for given az
apiVersion: litmuschaos.io/v1alpha1
kind: ChaosEngine
metadata:
  name: engine-nginx
spec:
  engineState: "active"
  chaosServiceAccount: litmus-admin
  experiments:
  - name: az-blackhole
    spec:
      components:
        env:
        # target subnet tags for the chaos
        - name: SUBNET_TAGS
          value: 'env:production,team:backend'
        # target availability zones for the chaos
        - name: AVAILABILITY_ZONES
          value: 'us-east-1a,us-east-1b'
        # target vpc ids for the chaos
        - name: VPC_IDS
          value: 'vpc-21312481928410'
        # region for chaos
        - name: REGION
          value: 'us-east-1'