fastly-compute-backend-production-setup

Fastly Compute Backend Production Setup

Problem

Backends defined in fastly.toml work during local development with fastly compute serve but return "Requested backend named 'X' does not exist" errors in production after deployment with fastly compute publish.

Context / Trigger Conditions

• Error: Requested backend named 'funnelcake' does not exist
• Error: TLS alert received (alert_id=0) when connecting to HTTPS backends
• Backend works with fastly compute serve locally
• fastly.toml has [[backends]] section properly configured
• Service was created before the backend was added to fastly.toml

Root Cause

The [[backends]] section in fastly.toml is only processed during initial service creation via the [setup] configuration. Once a service exists, changes to backends in fastly.toml are ignored - you must add/modify backends through the Fastly CLI or API.

From the Fastly CLI output:

INFO: Processing of the fastly.toml [setup] configuration happens only for a new service. Once a service is created, any further changes to the service or its resources must be made manually.

Solution

Step 1: Create the backend via CLI

fastly backend create \
  --service-id YOUR_SERVICE_ID \
  --version active \
  --autoclone \
  --name backend-name \
  --address api.example.com \
  --port 443 \
  --override-host api.example.com \
  --use-ssl \
  --ssl-cert-hostname api.example.com \
  --ssl-sni-hostname api.example.com

Key flags:

• --autoclone: Creates a new version automatically
• --ssl-cert-hostname: Required for SSL certificate validation
• --ssl-sni-hostname: Required for TLS SNI (fixes alert_id=0 errors)

Step 2: Activate the new version

fastly service-version activate --service-id YOUR_SERVICE_ID --version VERSION_NUMBER

Step 3: Verify backend exists

fastly backend list --service-id YOUR_SERVICE_ID --version active

Step 4: Redeploy your code

After adding the backend, redeploy to ensure the code and backend are in the same version: