Variables Reference

Variables Reference

Variables in Railway support references to other services, shared variables, and Railway-provided values.

Template Syntax

${{NAMESPACE.VAR}}

Examples

Reference shared variable:

{ "value": "${{shared.DOMAIN}}" }

Reference another service's variable:

{ "value": "${{api.API_KEY}}" }

Combine with text:

{ "value": "https://${{shared.DOMAIN}}/api" }

Railway-Provided Variables

Railway injects these into every service automatically.

Networking

Note: RAILWAY_PUBLIC_DOMAIN is only available if the service has a domain configured. Check the service's environment config to verify a domain exists before referencing it.

Context

Volume (if attached)

Git (if deployed from GitHub)

Wiring Services Together

Frontend → Backend (public network)

Use when: Browser makes requests to API (browser can't access private network)

{
  "services": {
    "<frontendId>": {
      "variables": {
        "API_URL": { "value": "https://${{backend.RAILWAY_PUBLIC_DOMAIN}}" }
      }
    }
  }
}

Service → Database (private network)

Use when: Backend connects to database (faster, no egress cost, more secure)

Railway databases auto-generate connection URL variables. Use the private versions:

Postgres/MySQL example:

{
  "services": {
    "<apiId>": {
      "variables": {
        "DATABASE_URL": { "value": "${{Postgres.DATABASE_URL}}" }
      }
    }
  }
}

Redis example:

{
  "services": {
    "<apiId>": {
      "variables": {
        "REDIS_URL": { "value": "${{Redis.REDIS_URL}}" }
      }
    }
  }
}

Mongo example:

{
  "services": {
    "<apiId>": {
      "variables": {
        "MONGO_URL": { "value": "${{Mongo.MONGO_URL}}" }
      }
    }
  }
}

Note: Service names are case-sensitive. Match the exact name from your project (e.g., "Postgres", "Redis").

Service → Service (private network)

Use when: Microservices communicate internally

{
  "services": {
    "<workerServiceId>": {
      "variables": {
        "API_INTERNAL_URL": { "value": "http://${{api.RAILWAY_PRIVATE_DOMAIN}}:${{api.PORT}}" }
      }
    }
  }
}

When to Use Public vs Private