140 lines
6 KiB
Markdown
140 lines
6 KiB
Markdown
# 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 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:
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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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## Enabling chaos endpoints
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For obvious reasons, these endpoints are not enabled by default on `production`.
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They are enabled by default on **development** environments.
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DANGER: **Danger:**
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It is required that you secure access to the chaos endpoints using a secret token.
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You should not enable them in production unless you absolutely know what you're doing.
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A secret token can be set through the `GITLAB_CHAOS_SECRET` environment variable.
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For example, when using the [GDK](https://gitlab.com/gitlab-org/gitlab-development-kit)
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this can be done with the following command:
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```bash
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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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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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To simulate a memory leak in your application, use the `/-/chaos/leakmem` endpoint.
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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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```
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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_s, 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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curl http://localhost:3000/-/chaos/leakmem?memory_mb=1024&duration_s=10&token=secret
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```
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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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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/cpu_spin
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GET /-/chaos/cpu_spin?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/cpu_spin?duration_s=60 --header 'X-Chaos-Secret: secret'
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curl http://localhost:3000/-/chaos/cpu_spin?duration_s=60&token=secret
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```
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## DB spin
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This endpoint attempts to fully utilise a single core, and interleave it with DB request, for the given period.
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This endpoint can be used to model yielding execution to another threads when running concurrently.
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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/db_spin
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GET /-/chaos/db_spin?duration_s=50
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```
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| Attribute | Type | Required | Description |
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| ------------ | ------- | -------- | --------------------------------------------------------------------- |
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| `interval_s` | float | no | Interval, in seconds, for every DB request. Defaults to 1s |
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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/db_spin?interval_s=1&duration_s=60 --header 'X-Chaos-Secret: secret'
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curl http://localhost:3000/-/chaos/db_spin?interval_s=1&duration_s=60&token=secret
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```
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## Sleep
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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_s.
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As with the CPU Spin endpoint, this may lead to your request timing out if duration_s exceeds the configured limit.
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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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curl http://localhost:3000/-/chaos/sleep?duration_s=60&token=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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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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```bash
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curl http://localhost:3000/-/chaos/kill --header 'X-Chaos-Secret: secret'
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curl http://localhost:3000/-/chaos/kill?token=secret
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```
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