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Cthulhu

Cthulhu is a Chaos Engineering tool that helps evaluating the resiliency of microservice systems. It does that by simulating various disaster scenarios against a target infrastructure in a data-driven manner.

Chaos Engineering

An ideal platform should be able to automatically detect failures and heal itself back to a normal state without any interruption of service. Running chaos scenarios expose gaps in the self-healing ability of a platform. Knowing about the short comings of the infrastruvcture allows engineering teams to become more efficient at recovering the system in the event of a disaster (either manually or by perfecting the self-healing features of the platform).

System Requirements

System Requirements will differ depending on the method you wish to use Cthulhu.

If running from docker you will need >Docker 17.05 If running from gradle you will need Java8

Running from Gradle

The following command will run a given chaos scenario and output the log to the console. See the module-specific instructions (below) on how to configure the container for them. To specify re-usable configurations for Cthulhu, copy ./src/main/resources/application-overrides-template.properties as ./src/main/resources/application-overrides.properties

./gradlew bootRun < <path-to-scenario>

Running from Docker

The following command will run a given chaos scenario in a docker container, output the log to the console, and clean-up the container once the process has completed. See the module-specific instructions (below) on how to configure the container for them.

   docker run -it --rm \
   -v <path-to-scenario>:/etc/cthulhu/scenario.yaml \
   xmattersinc/cthulhu

Environment variable mapping

Environment variables can be used to define/overwrite configuration values using the following pattern ABC_DEF --> abc.def.

Chaos Scenarios

Cthulhu executes Scenario files that contain a list of Chaos Events. The Scenario files are in YAML format. The following show the usage of all shared fields. Refer to module-specific instructions for Chaos Events.

Scenario

name — Name of the Scenario (used for logging).
chaosevents — One or more Chaos Event entry:

Chaos Event

description — Describes what this Chaos Event does (used for logging).
engine — The target infrastructure engine (see module-specific instructions).
operation — Operation to run (see module-specific instructions).
quantity — Subset of the matched instances to affect. The subset is taken randomly from the targets. If missing, all matches are affected.
schedule — Define delays and repetitions for the event (See the Schedule section). If missing, the event will be executed once immediately.
skip — Number of targets that will not be affected. This can be used in conjunction with schedule to ensure a service is kept below its normal availability level, while ensuring it is not completely disabled.
target — Expressions used by the Chaos Engine to identify instances to target.

Schedule

delay — Delay before executing each occurrence of an event (e.g. 30s).
delayjitter — Random amount of time added or removed from the delay (e.g. delay: 30s + delayjitter: 5s = 30s±5s).
initialdelay — Delay before executing the first occurrence of an event (e.g. 10m). If missing, delay is used.
repeat — Number of repetition of this event. If missing, the event will execute once.

Global Configuration

cthulhu.event.timeout.default — Default delay before cancelling Chaos Events.

Amazon Web Services Configuration

There is no configuration specific to AWS in Cthulhu. Configure the AWS console with the account that will run chaos events.

AWS Chaos Events

engine — Set to aws-ec2.
target — Follows this pattern: <zone>/<vm-name-tag>. Both Zone and VM Name supports regular expressions. Only VMs in the running state are considered for targets.

Delete VMs

operation — Set to delete.

Reset VMs

operation — Set to reset.

Stop Vms

operation — Set to stop.

Google Cloud Configuration

gcp.account.json — Path to a Google Cloud credential file.
- How to create a Google Cloud Service Account.
- To interact with VM instances, your service account must have the Compute Admin role.
gcp.project — The name of the Google Cloud project which to connect.

Docker Configurations for GCP

Passing-in a Google Cloud credential file: -v ~/.ssh/sa_dev_chaostest.json:/etc/secrets/gcp-account.json
Specifying a GCP project: -e GCP_PROJECT=<project-id>

GCP Chaos Events

engine — Set to gcp-compute.
target — Follows this pattern: <zone>/<vm-name>. Both Zone and VM Name supports regular expressions.

Delete VMs

operation — Set to delete.

Reset VMs

operation — Set to reset.

Stop Vms

operation — Set to stop.

Kubernetes Configuration

kube.config — Path to a Kubernetes config. By default, Cthulhu looks for the config file of the the current user ~/.kube/config and uses the current context.
- How get a K8s context for the Google Cloud Kubernetes Engine.
- To interact with containers, your service account must have the Kubernetes Engine Admin role.

Docker Configurations for K8s

Passing-in a Kube config file: -v ~/.kube/config:/etc/secrets/kube.config

K8s Chaos Events

engine — Set to kubernetes.
target — Follows this pattern: <namespace>/<pod-name>. Both Namespace and Pod Name supports regular expressions.

Delete Pods

operation — Set to delete.

Slack Notifications

slack.audit.filter — List of audit types to include in the Slack notifications (see the auditing section).
slack.audit.<audit-type>.message — Customize notifications per audit type. The placeholder %s can be used to indicate where to put the original notification message.
slack.channels — Override the default webhook channel. Supports multiple values, using the syntax #channelA #channelB.
slack.icon_emoji — Override the webhook avatar using an emoji (eg. :smiling_imp:).
slack.username — Override the webhook's display name.
slack.webhook.url — URL of a Slack incoming webhook.

Docker Configurations for Slack Notifications

Specifying a webhook URL: -e SLACK_WEBHOOK_URL=https://hooks.slack.com/services/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

Building Additional Chaos Engines

Each Chaos Engine has its own sub-project, which has a dependency on the api project. The main class must extends from com.xmatters.testing.cthulhu.api.eventrunner.ChaosEngine and be marked with the annotation com.xmatters.testing.cthulhu.api.annotations.EngineName. The value of EngineName will match the engine field in Chaos Events.

Once a new Chaos Engine is created, a reference must be added in the main build.gradle file.

Operation methods are public methods declared in the ChaosEngine, and marked with the annotation com.xmatters.testing.cthulhu.api.annotations.OperationName. The value of OperationName will match the operation field in Chaos Events. Operation methods must take an array parameter of the same type that is returned by the getTargets method.

The T[] getTargets(ChaosEvent ev) method must return an array of a concrete type. All possible matches of a target must be returned. skip and quantity are applied by the ChaosEventHandler before the final selection is then given to an operation method as parameter.

Building Additional Chaos Auditors

Each Chaos Auditor has its own sub-project, which has a dependency on the api project. The main class must implements com.xmatters.testing.cthulhu.api.auditing.ChaosAuditor. Additionally the same class can extend from com.xmatters.testing.cthulhu.api.configuration.ModuleConfiguration if it needs to configure itself.

Once a new Chaos Auditor is created, a reference must be added in the main build.gradle file.

Disclaimer

Cthulhu is not an officially supported xMatters product.

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