Render Web Services

This skill covers Web Service behavior on Render: how traffic reaches your process, how deploys go live, and how optional features (domains, disks, auto-deploy) interact. Use it alongside Blueprint and networking skills when wiring render.yaml or Dashboard settings.

When to Use

• Configuring or debugging port binding, PORT, or multi-port web services
• TLS/HTTPS expectations at the edge vs inside the container
• Health checks blocking or rolling back deploys
• Custom domains, DNS, and certificate provisioning
• Auto-deploy, CI-gated deploys, and PR preview generation
• Persistent disks and their impact on scaling and zero-downtime
• Deploy lifecycle: build, pre-deploy, swap, drain, rollback, shutdown delay

Deeper patterns live under references/ (health checks, domains, deploy phases).

Before configuring or troubleshooting deploys and health checks, read references/deployments.md. Before attaching or changing a persistent disk, read references/persistent-disks.md. Before configuring or troubleshooting private connectivity or additional ports, read references/private-networking.md.

Port Binding

• Listen on 0.0.0.0 (all interfaces). Binding only to localhost or 127.0.0.1 prevents Render’s proxy from reaching your app.
• Use the PORT environment variable for the HTTP listen port. Render sets it for you; the default is often 10000 and you can change the configured value in the service Settings in the Dashboard.
• Reserved ports (do not bind your application to these for normal traffic): 18012, 18013, 19099.

Multi-port Web Services

• Only one port receives public HTTP traffic: the port aligned with PORT.
• Additional open ports are reachable on Render’s private network only (not from the public internet through the same public URL pattern).

TLS and HTTPS

• TLS terminates at Render’s edge. The edge speaks HTTPS to clients; your process typically receives plain HTTP on PORT.
• HTTPS redirect for clients is handled by the platform; users hitting HTTP are redirected appropriately at the edge.
• Do not terminate TLS inside the app for the primary public listener unless you have a rare, explicit need—standard Web Services assume HTTP behind the proxy.

Health Checks

Follow references/deployments.md for current platform behavior. For endpoint implementations and common failure patterns, see references/health-check-patterns.md.

Custom Domains

• Point DNS with a CNAME to [service-name].onrender.com (use your service’s hostname from the Dashboard).
• Render automatically provisions and renews TLS certificates for verified domains.
• Apex (root) domains need provider-specific CNAME-like or flattened records where plain CNAME at @ is unsupported.
• Wildcard domains (e.g. *.example.com) are supported when configured and verified.
• Multiple custom domains per service are supported; Blueprints can list them under the domains field.

See references/custom-domains.md for Dashboard steps, verification, and troubleshooting.

Auto-Deploy and PR Previews

• Follow references/deployments.md for auto-deploy behavior and manual triggers.
• PR previews are configured under Blueprint previews.generation (and related preview settings); generation behavior depends on repo integration and plan.

Persistent Disks

• A disk-backed web service stays single-instance and cannot scale horizontally.
• Attaching a disk disables zero-downtime deploys.
• The disk is available only to the running service, not during builds or pre-deploy commands.
• If the workload needs horizontal scaling or uninterrupted deploys, use shared external storage instead of a service-attached disk.
• Follow references/persistent-disks.md for current support, configuration, mount-path, runtime-access, sizing, and snapshot behavior.

Deploy Lifecycle

For paid web services, use preDeployCommand for database migrations and other release tasks that must succeed before the new version receives traffic. It runs after the build on separate compute; if it fails, the deploy is canceled and the previous live version continues serving. Follow references/deployments.md for the full build, readiness, traffic-switching, draining, rollback, restart, and deploy-hook behavior.

Free Tier Notes

Free Web Services have separate limits: services spin down after inactivity (cold starts on the next request), and they do not support scaling beyond a single instance or persistent disks. Treat free-tier behavior as distinct from paid Web Service defaults when advising on uptime and scaling.

References

Topic	File
Health check design, timeouts, pitfalls	references/health-check-patterns.md
Domains, DNS, TLS verification	references/custom-domains.md
Deploy lifecycle, health checks, rollback, triggers	references/deployments.md
Persistent disk constraints and configuration	references/persistent-disks.md
Private-network addressing, ports, discovery, and troubleshooting	references/private-networking.md

Related Skills

• render-deploy — Blueprints, first-time deploy, render.yaml structure
• render-docker — Docker-based Web Services and image/runtime details
• render-networking — Private network, internal URLs, multi-port private listeners
• render-scaling — Instance counts, plans, and scaling constraints (including disk interactions)

Current documentation retrieval

Whenever this skill directs you to consult current Render documentation:

1. Retrieve the linked Markdown document directly with an available URL-fetching tool or HTTP client, such as curl. Do not substitute web-search summaries for the document.
2. Confirm that retrieval succeeded and returned the expected document, then read its contents. Saving a file or printing its path is not sufficient.
3. If the request fails or your tool cannot read the Markdown response, open and read the linked HTML version instead.
4. If neither version can be retrieved, disclose that the current reference is unavailable and follow any topic-specific fallback in the skill. Use bundled guidance only for stable constraints, and do not guess at changeable platform details.

When a task requires multiple references, apply this workflow to each one and distinguish the documents you verified from those that remain unavailable.