Variables

# Variables Reference Variables in Railway support references to other services, shared variables, and Railway-provided values. ## Template Syntax ``` ${{NAMESPACE.VAR}} ``` | Namespace | Description | |-----------|-------------| | `shared` | Shared variables (project-wide) | | `` | Variables from another service (case-sensitive) | ## Examples **Reference shared variable:** ```json { "value": "${{shared.DOMAIN}}" } ``` **Reference another service's variable:** ```json { "value": "${{api.API_KEY}}" } ``` **Combine with text:** ```json { "value": "https://${{shared.DOMAIN}}/api" } ``` ## Railway-Provided Variables Railway injects these into every service automatically. ### Networking | Variable | Description | Example | Availability | |----------|-------------|---------|--------------| | `RAILWAY_PUBLIC_DOMAIN` | Public domain | `myapp.up.railway.app` | Only if service has a domain | | `RAILWAY_PRIVATE_DOMAIN` | Private DNS (internal only) | `myapp.railway.internal` | Always | | `RAILWAY_TCP_PROXY_DOMAIN` | TCP proxy domain | `roundhouse.proxy.rlwy.net` | Only if TCP proxy enabled | | `RAILWAY_TCP_PROXY_PORT` | TCP proxy port | `11105` | Only if TCP proxy enabled | **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 | Variable | Description | |----------|-------------| | `RAILWAY_PROJECT_ID` | Project ID | | `RAILWAY_PROJECT_NAME` | Project name | | `RAILWAY_ENVIRONMENT_ID` | Environment ID | | `RAILWAY_ENVIRONMENT_NAME` | Environment name | | `RAILWAY_SERVICE_ID` | Service ID | | `RAILWAY_SERVICE_NAME` | Service name | | `RAILWAY_DEPLOYMENT_ID` | Deployment ID | | `RAILWAY_REPLICA_ID` | Replica ID | | `RAILWAY_REPLICA_REGION` | Region (e.g., `us-west2`) | ### Volume (if attached) | Variable | Description | |----------|-------------| | `RAILWAY_VOLUME_NAME` | Volume name | | `RAILWAY_VOLUME_MOUNT_PATH` | Mount path | ### Git (if deployed from GitHub) | Variable | Description | |----------|-------------| | `RAILWAY_GIT_COMMIT_SHA` | Commit SHA | | `RAILWAY_GIT_BRANCH` | Branch name | | `RAILWAY_GIT_REPO_NAME` | Repository name | | `RAILWAY_GIT_REPO_OWNER` | Repository owner | | `RAILWAY_GIT_AUTHOR` | Commit author | | `RAILWAY_GIT_COMMIT_MESSAGE` | Commit message | ## Wiring Services Together ### Frontend → Backend (public network) Use when: Browser makes requests to API (browser can't access private network) ```json { "services": { "": { "variables": { "API_URL": { "value": "https://${{backend.RAILWAY_PUBLIC_DOMAIN}}" } } } } } ``` ### Service → Database (private network) Use when: Backend connects to database (faster, no egress cost, more secure) Railway databases auto-generate connection URL variables. Use the private versions: | Database | Variable Reference | |----------|-------------------| | Postgres | `${{Postgres.DATABASE_URL}}` | | MySQL | `${{MySQL.DATABASE_URL}}` | | Redis | `${{Redis.REDIS_URL}}` | | Mongo | `${{Mongo.MONGO_URL}}` | **Postgres/MySQL example:** ```json { "services": { "": { "variables": { "DATABASE_URL": { "value": "${{Postgres.DATABASE_URL}}" } } } } } ``` **Redis example:** ```json { "services": { "": { "variables": { "REDIS_URL": { "value": "${{Redis.REDIS_URL}}" } } } } } ``` **Mongo example:** ```json { "services": { "": { "variables": { "MONGO_URL": { "value": "${{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 ```json { "services": { "": { "variables": { "API_INTERNAL_URL": { "value": "http://${{api.RAILWAY_PRIVATE_DOMAIN}}:${{api.PORT}}" } } } } } ``` ## When to Use Public vs Private | Use Case | Domain | Reason | |----------|--------|--------| | Browser → API | Public | Browser can't access private network | | Service → Service | Private | Faster, no egress, more secure | | Service → Database | Private | Databases should never be public | | External webhook → Service | Public | External services need public access | | Cron job → API | Private | Internal communication |