Diagnose Deployment Failures for FastAPI

Summary

Deployment diagnostics for a FastAPI app on Ample. Verified on FastAPI: the same app deployed with a deliberate boot failure (CANARY_FAIL=boot): ample deploy exited 1 with a coded failure (health_check_failed when the process dies at boot, public_ingress_failed when the framework boots but every request answers 500) and the app's own error line was readable with ample logs --kind runtime, so the cause is read from the framework's output rather than guessed. Build and start: pip install into .ample/python from requirements.txt, then uvicorn from run.py reading PORT on the python-3.12 template.

Prerequisites

• A FastAPI project (pip install into .ample/python from requirements.txt, then uvicorn from run.py reading PORT on the python-3.12 template)
• An Ample account token with servers:write

Workflow Steps

1. Read the failure code
   Deploy is synchronous. Exit 1 with build_failed means the isolated build failed; health_check_failed means the app built but never answered on PORT (it crashed at boot or bound the wrong port); public_ingress_failed means it answered on PORT but the public URL returned an error status (a request handler or bootstrap failed); exit 2 means a required preflight action is blocking.

2. Read the build log
   The last lines name the failing command and its output.
   Command: ample logs --kind build

3. Read the runtime log
   For health_check_failed the runtime log carries the FastAPI process output: in the verified run the deliberate boot failure's own error line was there, followed by the platform's health-check verdict and the start command it ran.
   Command: ample logs --kind runtime

4. Fix and redeploy once
   Change the source, the environment or the command override, then run ample deploy again. Do not loop deploys to poll status; an unchanged redeploy is a no-op.

5. Verify
   Fetch the live URL on the example; on failure read the build and runtime logs.
   Command: ample logs --kind build

Success Checks

• failed deploy reports health_check_failed synchronously
  expect: ample deploy exits 1 with error.code health_check_failed
• runtime log carries the app's own error line
  expect: ample logs --kind runtime shows the framework's error output before the health-check verdict

Limitations

• Verified on the python-3.12 template at s-1vcpu-1gb; other sizes and FastAPI major versions are not verified.
• Region, compliance attestations and request-duration limits are unknown and not claimed.

Cost Estimate

• Currency: USD
• Monthly Amount: 5.0
• Basis: size prices from pricing.toml (loaded by the API) at build revision 1ac5595375130d45290090e82ed0f554ccd45405-dirty
• Components:
  • app server, size: s-1vcpu-1gb, quantity: 1.0, monthlyAmount: 5.0
• Note: Always-on monthly price of the tested sizes; apps auto-pause when idle. Buckets are allocation-priced per quota and not included.

Evidence Summary

• Kind: canary_run
• Summary: FastAPI pattern fixture deployed on Ample with CANARY_FAIL=boot (pip install into .ample/python from requirements.txt, then uvicorn from run.py reading PORT on the python-3.12 template); the same app deployed with a deliberate boot failure (CANARY_FAIL=boot): ample deploy exited 1 with a coded failure (health_check_failed when the process dies at boot, public_ingress_failed when the framework boots but every request answers 500) and the app's own error line was readable with ample logs --kind runtime, so the cause is read from the framework's output rather than guessed.
• Observed At: 2026-09-21T02:23:07Z
• Implementation Revision: 50dbac567d2c5cc8e55e6c748a646be0025d9cfb-dirty (CLI 0.1.21)
• Expires At: 2027-03-20T02:23:07Z