Documentation updates as per review [skip ci]
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Andrew Newdigate
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# Generating Chaos in a test GitLab instance
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# Generating chaos in a test GitLab instance
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As [Werner Vogels](https://twitter.com/Werner), the CTO at Amazon Web Services, famously put it, **Everything fails, all the time**.
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As a developer, it's as important to consider the failure modes in which your software will operate as much as normal operation. Doing so can mean the difference between a minor hiccup leading to a scattering of 500 errors experienced by a tiny fraction of users and a full site outage affect all users for an extended period.
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As a developer, it's as important to consider the failure modes in which your software will operate as much as normal operation. Doing so can mean the difference between a minor hiccup leading to a scattering of `500` errors experienced by a tiny fraction of users and a full site outage that affects all users for an extended period.
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To paraphrase [Tolstoy](https://en.wikipedia.org/wiki/Anna_Karenina_principle), _all happy servers are alike, but all failing servers are failing in their own way_. Luckily, there are ways we can attempt to simulate these failure modes, and the chaos endpoints are tools for assisting in this process.
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Currently, there are four endpoints for simulating the following conditions: slow requests, cpu-bound requests, memory leaks and unexpected process crashes.
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Currently, there are four endpoints for simulating the following conditions:
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## Enabling Chaos Endpoints
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- Slow requests.
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- CPU-bound requests.
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- Memory leaks.
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- Unexpected process crashes.
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For obvious reasons, these endpoints are not enabled by default. They can be enabled by setting the `GITLAB_ENABLE_CHAOS_ENDPOINTS` environment variable.
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## Enabling chaos endpoints
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For obvious reasons, these endpoints are not enabled by default. They can be enabled by setting the `GITLAB_ENABLE_CHAOS_ENDPOINTS` environment variable to `1`.
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For example, if you're using the [GDK](https://gitlab.com/gitlab-org/gitlab-development-kit) this can be done with the following command:
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```shell
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```bash
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GITLAB_ENABLE_CHAOS_ENDPOINTS=1 gdk run
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```
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### Securing the Chaos Endpoints
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## Securing the chaos endpoints
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**It is highly recommended that you secure access to the Chaos endpoints using a secret token**. This is recommended when enabling these endpoints locally, and essential when running in a staging or other shared environment. _It goes without saying that you should not enable them in production unless you absolutely know what you're doing._
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DANGER: **Danger:**
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It is highly recommended that you secure access to the chaos endpoints using a secret token. This is recommended when enabling these endpoints locally and essential when running in a staging or other shared environment. You should not enable them in production unless you absolutely know what you're doing.
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A secret can be set through the `GITLAB_CHAOS_SECRET` environment variable. For example, when using the [GDK](https://gitlab.com/gitlab-org/gitlab-development-kit) this can be done with the following command line:
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A secret token can be set through the `GITLAB_CHAOS_SECRET` environment variable. For example, when using the [GDK](https://gitlab.com/gitlab-org/gitlab-development-kit) this can be done with the following command:
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```shell
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```bash
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GITLAB_ENABLE_CHAOS_ENDPOINTS=1 GITLAB_CHAOS_SECRET=secret gdk run
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```
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Replace `secret` with your own secret token.
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## Invoking Chaos
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## Invoking chaos
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Once you have enabled the chaos endpoints and restarted the application you can start testing using the endpoints.
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Once you have enabled the chaos endpoints and restarted the application, you can start testing using the endpoints.
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### Memory Leaks
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## Memory leaks
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To simulate a memory leak in your application, use the `/-/chaos/leakmem` endpoint.
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For example, if your GitLab instance is listening at `localhost:3000`, you could `curl` the endpoint as follows:
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NOTE: **Note:**
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The memory is not retained after the request finishes. Once the request has completed, the Ruby garbage collector will attempt to recover the memory.
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```shell
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```
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GET /-/chaos/leakmem
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GET /-/chaos/leakmem?memory_mb=1024
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GET /-/chaos/leakmem?memory_mb=1024&duration_s=50
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```
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| Attribute | Type | Required | Description |
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| ------------ | ------- | -------- | ---------------------------------------------------------------------------------- |
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| `memory_mb` | integer | no | How much memory, in MB, should be leaked. Defaults to 100MB. |
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| `duration_s` | integer | no | Minimum duration, in seconds, that the memory should be retained. Defaults to 30s. |
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```bash
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curl http://localhost:3000/-/chaos/leakmem?memory_mb=1024&duration_s=10 --header 'X-Chaos-Secret: secret'
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```
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The `memory_mb` parameter tells the application how much memory it should leak. The `duration_s` parameter will ensure the request retains
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the memory for this duration at a minimum (default 30s).
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Note: the memory is not retained after the request finishes. Once the request has completed, the Ruby garbage collector will attempt to recover the memory.
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### CPU Spin
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## CPU spin
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This endpoint attempts to fully utilise a single core, at 100%, for the given period.
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```shell
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Depending on your rack server setup, your request may timeout after a predermined period (normally 60 seconds).
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If you're using Unicorn, this is done by killing the worker process.
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```
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GET /-/chaos/cpuspin
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GET /-/chaos/cpuspin?duration_s=50
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```
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| Attribute | Type | Required | Description |
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| ------------ | ------- | -------- | --------------------------------------------------------------------- |
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| `duration_s` | integer | no | Duration, in seconds, that the core will be utilised. Defaults to 30s |
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```bash
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curl http://localhost:3000/-/chaos/cpuspin?duration_s=60 --header 'X-Chaos-Secret: secret'
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```
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The `duration_s` parameter will configure how long the core is utilised.
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## Sleep
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Depending on your rack server setup, your request may timeout after a predermined period (normally 60 seconds). If you're using Unicorn, this is done by killing the worker process.
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### Sleep
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This endpoint is similar to the CPU Spin endpoint but simulates off-processor activity, such backend services of IO. It will sleep for a given duration.
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```shell
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curl http://localhost:3000/-/chaos/sleep?duration_s=60 --header 'X-Chaos-Secret: secret'
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```
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The `duration_s` parameter will configure how long the request will sleep for.
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This endpoint is similar to the CPU Spin endpoint but simulates off-processor activity, such as network calls to backend services. It will sleep for a given duration.
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As with the CPU Spin endpoint, this may lead to your request timing out if duration exceeds the configured limit.
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### Kill
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```
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GET /-/chaos/sleep
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GET /-/chaos/sleep?duration_s=50
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```
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| Attribute | Type | Required | Description |
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| ------------ | ------- | -------- | ---------------------------------------------------------------------- |
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| `duration_s` | integer | no | Duration, in seconds, that the request will sleep for. Defaults to 30s |
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```bash
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curl http://localhost:3000/-/chaos/sleep?duration_s=60 --header 'X-Chaos-Secret: secret'
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```
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## Kill
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This endpoint will simulate the unexpected death of a worker process using a `kill` signal.
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```shell
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curl http://localhost:3000/-/chaos/kill --header 'X-Chaos-Secret: secret'
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NOTE: **Note:**
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Since this endpoint uses the `KILL` signal, the worker is not given a chance to cleanup or shutdown.
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```
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GET /-/chaos/kill
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```
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Note: since this endpoint uses the `KILL` signal, the worker is not given a chance to cleanup or shutdown.
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```bash
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curl http://localhost:3000/-/chaos/kill --header 'X-Chaos-Secret: secret'
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```
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@ -34,14 +34,14 @@ graphs/dashboards.
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## Tooling
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GitLab provides built-in tools to aid the process of improving performance:
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GitLab provides built-in tools to help improve performance and availability:
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* [Profiling](profiling.md)
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* [Sherlock](profiling.md#sherlock)
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* [GitLab Performance Monitoring](../administration/monitoring/performance/index.md)
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* [Request Profiling](../administration/monitoring/performance/request_profiling.md)
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* [QueryRecoder](query_recorder.md) for preventing `N+1` regressions
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* [Chaos Endpoints](chaos_endpoints.md) less for performance, more for availability: tools for testing failure scenarios
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* [Chaos endpoints](chaos_endpoints.md) for testing failure scenarios. Intended mainly for testing availability.
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GitLab employees can use GitLab.com's performance monitoring systems located at
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<https://dashboards.gitlab.net>, this requires you to log in using your
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