# Ruby on Rails

> Monitor a Rails app: a Rack middleware writing one JSON line per request with status, Devise and Warden hooks for sign-ins, and beam monitor with the Rails rules.

Source: https://docs.agentbeam.com/cookbooks/frameworks/rails

## How Beam reads a Rails app

There's no in-process SDK for this stack, so the app writes what Beam needs to its logs and [`beam monitor`](https://docs.agentbeam.com/agent-cli/app-monitoring#install-and-start) reads them on the same server or container. Only redacted findings leave it. Two kinds of line:

- **One JSON line per request**, with `method`, `path` (with the query string), `status`, `ip`, `user_agent`, `host` and `duration_ms`. The status is what lets Beam tell an attack your app refused from one it answered.
- **Security events as plain lines**, worded like this (Beam matches the wording and reads `user=` and `ip=`):

```text
login failed user=42 ip=203.0.113.7
login succeeded user=42 ip=203.0.113.7
granted admin role to user=99 by user=12
API key created user=12
{"event":"llm_usage","user":"42","model":"gpt-5","total_tokens":1834}
```

Use an opaque user id, never an email. New outbound hosts are only reported by the Node.js SDK; for this stack, restrict outbound traffic at the network instead.

## Before you start

Do steps 1 and 2 of the [general cookbook](https://docs.agentbeam.com/cookbooks/app-monitoring#step-1-turn-it-on-and-create-the-apps-token) first: App monitoring is on, the app is added, and its `beam_app_` token is in your secret store as `BEAM_APP_TOKEN`. Everything below needs `@agent-beam/beam` 0.2.32 or newer.

## Log each request with its status

```ruby
# lib/beam_request_log.rb
require "json"
require "logger"

class BeamRequestLog
  LOG = Logger.new("/var/log/app/requests.log", formatter: ->(*, msg) { "#{msg}\n" })

  def initialize(app) = @app = app

  def call(env)
    started = Process.clock_gettime(Process::CLOCK_MONOTONIC)
    status, headers, body = @app.call(env)
    request = ActionDispatch::Request.new(env)
    LOG.info(JSON.generate(
      method: request.request_method,
      path: request.fullpath,
      status: status,
      ip: request.remote_ip,
      user_agent: request.user_agent.to_s,
      host: request.host,
      duration_ms: ((Process.clock_gettime(Process::CLOCK_MONOTONIC) - started) * 1000).round,
    ))
    [status, headers, body]
  end
end
```

```ruby
# config/application.rb
require_relative "../lib/beam_request_log"
config.middleware.insert_before 0, BeamRequestLog
```

`request.remote_ip` honors your trusted proxies (`config.action_dispatch.trusted_proxies`).

## Log sign-ins, admins and keys

With Devise (Warden):

```ruby
# config/initializers/beam_security.rb
BEAM_SECURITY = Logger.new("/var/log/app/security.log", formatter: ->(*, msg) { "#{msg}\n" })

Warden::Manager.after_authentication do |user, auth, _opts|
  BEAM_SECURITY.info("login succeeded user=#{user.id} ip=#{auth.request.remote_ip}")
end

Warden::Manager.before_failure do |env, _opts|
  request = ActionDispatch::Request.new(env)
  user_id = User.find_by(email: request.params.dig("user", "email"))&.id
  BEAM_SECURITY.warn("login failed user=#{user_id} ip=#{request.remote_ip}")
end
```

Where you grant admin rights or issue keys:

```ruby
BEAM_SECURITY.info("granted admin role to user=#{target.id} by user=#{current_user.id}")
BEAM_SECURITY.info("API key created user=#{current_user.id}")
BEAM_SECURITY.info({ event: "llm_usage", user: current_user.id.to_s, model: model, total_tokens: usage["total_tokens"] }.to_json)
```

## Run `beam monitor` next to the app

```sh
npm install -g @agent-beam/beam
beam monitor --stack rails --file /var/log/app/requests.log --file /var/log/app/security.log --app /srv/app
```

`--stack rails` turns on this framework's rules and rolls up attacks on frameworks you don't run; `--app` also checks the app's lockfiles daily (and would detect the stack on its own). Keep it running with systemd:

```ini
# /etc/systemd/system/beam-monitor.service
[Unit]
Description=AgentBeam App monitoring
After=network-online.target

[Service]
EnvironmentFile=/etc/beam/app.env
ExecStart=/usr/bin/env beam monitor --stack rails --file /var/log/app/requests.log --file /var/log/app/security.log --app /srv/app
Restart=always
User=beam

[Install]
WantedBy=multi-user.target
```

```sh
sudo install -m 600 /dev/null /etc/beam/app.env && echo "BEAM_APP_TOKEN=beam_app_..." | sudo tee /etc/beam/app.env >/dev/null
sudo systemctl daemon-reload && sudo systemctl enable --now beam-monitor
```

In Docker or Kubernetes, run the same command in a sidecar that mounts the log directory read-only, with `BEAM_APP_TOKEN` from a secret.
## Prove it works

```sh
beam monitor status   # app, level, stack, usage
beam monitor test     # a test finding through your alert workflows
curl -s "https://your-app.example.com/?id=1%20UNION%20SELECT%201" -o /dev/null
```

Within a minute, the SQL injection test shows on **App monitoring**: under **Needs action** if the app answered 2xx, or counted under "needed nothing from you" if it refused it. Then sign in to a test account with a wrong password ten times and the right one once: **Sign-in succeeded after 10 failed attempts** appears as critical.
## Check dependencies on every pull request

```yaml
# .github/workflows/beam-cve.yml
name: Dependency check
on: [pull_request]
jobs:
  cve:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - run: npx -y @agent-beam/beam cve check . --fail-on high
        env:
          BEAM_APP_TOKEN: ${{ secrets.BEAM_APP_TOKEN }}
```

`Gemfile.lock` is checked.
## What Beam watches for on this stack

Besides every [built-in rule](https://docs.agentbeam.com/agent-cli/app-monitoring#levels-and-detection) and the [attack-in-progress signals](https://docs.agentbeam.com/agent-cli/app-monitoring#signs-an-attack-is-underway):

| Rule | Means | Severity |
| --- | --- | --- |
| Rails info pages served publicly | `/rails/info/properties` or `/rails/info/routes` answered 2xx (development-only pages) | High |
| Template injection | ERB-style `<%= 7*7 %>` payloads | High |

Attacks on other frameworks (WordPress probes, Laravel or Spring exploits, and so on) are rolled up as **Not your stack** when there's no status to say otherwise, and never alert.
## Close what Beam would catch

Beam raises these when they're found; better that there's nothing to find:

- Run production with `RAILS_ENV=production`; `/rails/info` must never answer there.
- Keep `config.consider_all_requests_local = false` in production.
- Rate-limit sign-ins (Rack::Attack) and enable Devise's `lockable`.
## Coverage checklist

| Feature | Done when |
| --- | --- |
| Request log with status | Findings show **Answered**, **Refused** or **Errored** |
| Stack declared | `beam monitor` prints the stack at start |
| Sign-in events | `login failed` and `login succeeded` lines are written |
| Admin and key events | Role grants and new keys are logged |
| LLM spend | An `llm_usage` line follows each model call |
| Dependency checks | The CI job runs on pull requests |
| Alerts | Critical pages someone, high reaches a channel ([step 8](https://docs.agentbeam.com/cookbooks/app-monitoring#step-8-send-alerts-to-the-right-place)) |
| Routine | Someone reads **Needs action** daily and **Attack analytics** weekly |