Derailer is a tool that helps test for how services handle random dependency failures, on Railway. Inspired by Netflix's Chaos Monkey. Derailer randomly removes instances of running services. Allowing you to build more resilient services by finding missed opportunities to handle failures gracefully.

[CAUTION] You should avoid deploying this onto your customer facing environment, as it may have visible impact, we suggest sticking to staging!

If you've read the above disclaimer and understand it, click to deploy

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▶️ Derailment Process

Every so often (defined in FREQUENCY_CRON), the Derailer lists your Railway services and filters them to ones that aren't in the configured blacklist.

Using this list, it chooses to 'Derail' a number of your services (using BLAST_RADIUS), this is done by Aborting Deployments, it will remove the currently active deployment of your service.

After the defined DURATION_MINUTES, it will re-deploy any effected services.

The derailed services are stored in a persistent volume (on MongoDB), meaning re-deploying this service will restore any effected services when it comes online!

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👀 User Interface

[WARNING] This user interface is not password protected, we suggest using a cloudflare tunnel, or implementing your own authentication in a forked version.

Derailer comes with a (very primitive) user interface for controlling how the derailer behaves.

Features:

• Viewing an active derailment and what services it's impacting
• Rollback an active derailment if it's causing a headache
• Viewing when the next derailment will occur
• Viewing a history of which services were impacted for each past derailment
• Pausing derailments for a certain time period (to allow for some rest!)

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🤖 Rest API

[WARNING] This API is not password protected, we suggest using a cloudflare tunnel, or implementing your own authentication in a forked version.

For ease of use, all the features mentioned in our user interface are supported within a REST API, check out the API documentation.

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🧩 Configuration Options

Environment Variables

Variable	Description	Default Value
RAILWAY_API_KEY	Your Railway API key, required to list your services and fetch your running deployments
FREQUENCY_CRON	A chron expression defining how often to run the derailer	0 0 * * * ?
DURATION_MINUTES	How long (in minutes) to keep deployments aborted	60
BLAST_RADIUS	How many services to impact in each run of the Derailer	2

Blacklisting services

By default, the only service automatically blacklisted is the Derailer application. However, you may want to blacklist some UIs, monitoring systems, or essential services (think carefully about how reliable they are!) to avoid everything falling on its face.

This can be configured in src/main/resources/application.properties (derailment.blacklist)

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💻 Running Locally

Running locally allows you to quickly test your changes, using the Quarkus framework we can

Copy .env-example into a file called .env and fill in all the environment vars Run ./gradlew quarkusDev from the gradle quarkus menu to run in dev mode