Fly.io (flyctl) CLI

Operate Fly.io apps safely and repeatably with flyctl.

Common tasks

• Deploy: fly deploy / fly deploy --remote-only
• Logs: fly logs -a <app>
• SSH / run commands: fly ssh console -a <app> -C "…"
• Secrets: fly secrets list/set -a <app>
• Postgres: fly postgres list/connect/db create/attach
• GitHub Actions deploys / PR previews

Defaults / safety

• Prefer read-only commands first: fly status, fly logs, fly config show, fly releases, fly secrets list.
• Do not run state-changing Fly.io commands without explicit user approval (deploy/scale, secrets set/unset, volume/db create/drop, app destroy, attach/detach).
  • Read-only actions are OK without approval.
  • Destructive actions (destroy/drop) always require explicit approval.
• When debugging, classify the failure as: build/packaging vs runtime vs platform.

Quick start (typical deploy)

From the app repo directory:

1. Confirm which app you’re targeting

• fly app list
• fly status -a <app>
• Check fly.toml for app = "..."

2. Deploy

• fly deploy (default)
• fly deploy --remote-only (common when local docker/build env is inconsistent)

3. Validate

• fly status -a <app>
• fly logs -a <app>
• fly open -a <app>

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, SSH, console

• Stream logs:
  • fly logs -a <app>
• SSH console:
  • fly ssh console -a <app>
• Run a one-off command:
  • fly ssh console -a <app> -C "bin/rails db:migrate"

Secrets / config

• List secrets:
  • fly secrets list -a <app>
• Set secrets:
  • fly secrets set -a <app> KEY=value OTHER=value
• Show config:
  • fly config show -a <app>

Fly Postgres basics

Identify the Postgres app

• fly postgres list

Attach Postgres to an app

• fly postgres attach <pg-app> -a <app>

Create a database inside the cluster

• fly postgres db create <db_name> -a <pg-app>
• fly postgres db list -a <pg-app>

Connect (psql)

• fly postgres connect -a <pg-app>

GitHub Actions deploys / previews

• For production CD: use Fly’s GitHub Action (superfly/flyctl-actions/setup-flyctl) and run fly deploy (often with --remote-only).
• 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/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.