Fly.io CLI

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name: flyio-cli description: "Use the Fly.io flyctl CLI for deploying and operating apps on Fly.io. Default to read-only diagnostics (status/logs/config/releases). Only perform state-changing operations (deploys, SSH exec, secrets, scaling, machines, volumes, Postgres changes) with explicit user approval. Use when asked to deploy to Fly.io, debug fly deploy/build/runtime failures, set up GitHub Actions deploys/previews, or safely manage Fly apps and Postgres."

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Fly.io (flyctl) CLI

Operate Fly.io apps safely and repeatably with flyctl.

Defaults / safety

Prefer read-only commands first: fly status, fly logs, fly config show, fly releases, fly secrets list.

Do not edit/modify Fly.io apps, machines, secrets, volumes, or databases without your human’s explicit approval.

- Read-only actions are OK without approval. - Destructive actions (destroy/drop) always require explicit approval.

When debugging builds, capture the exact error output and determine whether it’s a:

- build/packaging issue (Dockerfile, Gemfile.lock platforms, assets precompile) - runtime issue (secrets, DB, migrations) - platform issue (regions, machines, health checks)

Quick start (typical deploy)

From the app repo directory:

1) Confirm which app you’re targeting

fly app list

fly status -a

Check fly.toml for app = "..."

2) Validate / inspect (read-only)

fly status -a

fly logs -a

fly config show -a

(Deploys are in High-risk operations below and require explicit user approval.)

Debugging deploy/build failures

Common checks

fly deploy --verbose (more build logs)

If using Dockerfile builds: verify Dockerfile Ruby/version and Gemfile.lock platforms match your builder OS/arch.

Rails + Docker + native gems (nokogiri, pg, etc.)

Symptoms: Bundler can’t find a platform gem like nokogiri-…-x86_64-linux during build.

Fix pattern:

Ensure Gemfile.lock includes the Linux platform used by Fly’s builder (usually x86_64-linux).

- Example: bundle lock --add-platform x86_64-linux

Ensure Dockerfile’s Ruby version matches .ruby-version.

(See references/rails-docker-builds.md.)

Logs & config (read-only)

Stream logs:

- fly logs -a

Show config:

- fly config show -a

List secrets (names only):

- fly secrets list -a

High-risk operations (ask first)

These commands can execute arbitrary code on servers or mutate production state. Only run them when the user explicitly asks you to.

Deploy:

- fly deploy / fly deploy --remote-only

SSH exec / console:

- fly ssh console -a -C ""

Secrets changes:

- fly secrets set -a KEY=value

See references/safety.md.

Fly Postgres basics

Identify the Postgres app

fly postgres list

Attach Postgres to an app

fly postgres attach -a

Create a database inside the cluster

fly postgres db create -a

fly postgres db list -a

Connect (psql)

fly postgres connect -a

GitHub Actions deploys / previews

For production CD: use Fly’s GitHub Action (superfly/flyctl-actions/setup-flyctl) and run flyctl deploy.

For PR previews:

- Prefer one preview app per PR and one database per PR inside a shared Fly Postgres cluster. - Automate create/deploy/comment on PR; destroy on close.

(See references/github-actions.md.)

Bundled resources

references/safety.md: safety rules (read-only by default; ask before mutating state).

references/rails-docker-builds.md: Rails/Docker/Fly build failure patterns + fixes.

references/github-actions.md: Fly deploy + preview workflows.

scripts/fly_app_from_toml.sh: tiny helper to print the Fly app name from fly.toml (shell-only; no ruby).