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:

Confirm which app you’re targeting

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

Validate / inspect (read-only)

```
fly status -a <app>
```
```
fly logs -a <app>
```
```
fly config show -a <app>
```

(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 <app>
```
Show config:
- ```
fly config show -a <app>
```
List secrets (names only):
- ```
fly secrets list -a <app>
```

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 <app> -C "<command>"
```
Secrets changes:
- ```
fly secrets set -a <app> KEY=value
```

See

references/safety.md

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
```
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).

Fly.io CLI

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Fly.io (flyctl) CLI

Defaults / safety

Quick start (typical deploy)

Debugging deploy/build failures

Common checks

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

Logs & config (read-only)

High-risk operations (ask first)

Fly Postgres basics

Identify the Postgres app

Attach Postgres to an app

Create a database inside the cluster

Connect (psql)

GitHub Actions deploys / previews

Bundled resources

Quick Start

Manual Installation

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