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diff --git a/doc/development/chaos_endpoints.md b/doc/development/chaos_endpoints.md new file mode 100644 index 00000000000..403a5b21827 --- /dev/null +++ b/doc/development/chaos_endpoints.md @@ -0,0 +1,117 @@ +# Generating chaos in a test GitLab instance + +As [Werner Vogels](https://twitter.com/Werner), the CTO at Amazon Web Services, famously put it, **Everything fails, all the time**. + +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. + +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. + +Currently, there are four endpoints for simulating the following conditions: + +- Slow requests. +- CPU-bound requests. +- Memory leaks. +- Unexpected process crashes. + +## Enabling chaos endpoints + +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`. + +For example, if you're using the [GDK](https://gitlab.com/gitlab-org/gitlab-development-kit) this can be done with the following command: + +```bash +GITLAB_ENABLE_CHAOS_ENDPOINTS=1 gdk run +``` + +## Securing the chaos endpoints + +DANGER: **Danger:** +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. + +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: + +```bash +GITLAB_ENABLE_CHAOS_ENDPOINTS=1 GITLAB_CHAOS_SECRET=secret gdk run +``` + +Replace `secret` with your own secret token. + +## Invoking chaos + +Once you have enabled the chaos endpoints and restarted the application, you can start testing using the endpoints. + +## Memory leaks + +To simulate a memory leak in your application, use the `/-/chaos/leakmem` endpoint. + +NOTE: **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. + +``` +GET /-/chaos/leakmem +GET /-/chaos/leakmem?memory_mb=1024 +GET /-/chaos/leakmem?memory_mb=1024&duration_s=50 +``` + +| Attribute | Type | Required | Description | +| ------------ | ------- | -------- | ---------------------------------------------------------------------------------- | +| `memory_mb` | integer | no | How much memory, in MB, should be leaked. Defaults to 100MB. | +| `duration_s` | integer | no | Minimum duration, in seconds, that the memory should be retained. Defaults to 30s. | + +```bash +curl http://localhost:3000/-/chaos/leakmem?memory_mb=1024&duration_s=10 --header 'X-Chaos-Secret: secret' +``` + +## CPU spin + +This endpoint attempts to fully utilise a single core, at 100%, for the given period. + +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. + +``` +GET /-/chaos/cpuspin +GET /-/chaos/cpuspin?duration_s=50 +``` + +| Attribute | Type | Required | Description | +| ------------ | ------- | -------- | --------------------------------------------------------------------- | +| `duration_s` | integer | no | Duration, in seconds, that the core will be utilised. Defaults to 30s | + +```bash +curl http://localhost:3000/-/chaos/cpuspin?duration_s=60 --header 'X-Chaos-Secret: secret' +``` + +## Sleep + +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. + +As with the CPU Spin endpoint, this may lead to your request timing out if duration exceeds the configured limit. + +``` +GET /-/chaos/sleep +GET /-/chaos/sleep?duration_s=50 +``` + +| Attribute | Type | Required | Description | +| ------------ | ------- | -------- | ---------------------------------------------------------------------- | +| `duration_s` | integer | no | Duration, in seconds, that the request will sleep for. Defaults to 30s | + +```bash +curl http://localhost:3000/-/chaos/sleep?duration_s=60 --header 'X-Chaos-Secret: secret' +``` + +## Kill + +This endpoint will simulate the unexpected death of a worker process using a `kill` signal. + +NOTE: **Note:** +Since this endpoint uses the `KILL` signal, the worker is not given a chance to cleanup or shutdown. + +``` +GET /-/chaos/kill +``` + +```bash +curl http://localhost:3000/-/chaos/kill --header 'X-Chaos-Secret: secret' +``` |