Quick Start

Get Sentinel up and running in under 5 minutes.

1. Install Sentinel

Run the install script:

curl -fsSL https://getsentinel.raskell.io | sh

Add to your PATH if needed:

export PATH="$HOME/.local/bin:$PATH"

Verify it works:

sentinel --version

2. Create a Configuration File

Create sentinel.kdl in your current directory:

server {
    worker-threads 0
}

listeners {
    listener "http" {
        address "0.0.0.0:8080"
        protocol "http"
    }
}

routes {
    route "api" {
        matches {
            path-prefix "/api/"
        }
        upstream "api-backend"
    }

    route "default" {
        priority "low"
        matches {
            path-prefix "/"
        }
        upstream "web-backend"
    }
}

upstreams {
    upstream "api-backend" {
        targets {
            target { address "127.0.0.1:3000" }
        }
    }

    upstream "web-backend" {
        targets {
            target { address "127.0.0.1:3001" }
        }
    }
}

observability {
    metrics {
        enabled true
        address "0.0.0.0:9090"
    }
    logging {
        level "info"
        format "json"
    }
}

3. Start a Test Backend

For testing, start a simple backend server:

# Using Python (port 3000)
python3 -m http.server 3000 &

# Or using Node.js
npx http-server -p 3000 &

4. Run Sentinel

sentinel -c sentinel.kdl

You should see:

INFO sentinel starting up
INFO listener http listening on 0.0.0.0:8080
INFO metrics server listening on 0.0.0.0:9090

5. Test It

In a new terminal:

# Test the proxy
curl http://localhost:8080/

# Check metrics
curl http://localhost:9090/metrics

What’s Happening

  1. Listener accepts HTTP connections on port 8080
  2. Router matches requests against route rules:
    • /api/* requests go to api-backend (port 3000)
    • All other requests go to web-backend (port 3001)
  3. Upstream forwards requests to your backend servers
  4. Metrics are exposed on port 9090 for monitoring

Add Health Checks

Update your config to add health checks:

upstreams {
    upstream "api-backend" {
        targets {
            target { address "127.0.0.1:3000" }
        }
        health-check {
            type "http" {
                path "/health"
            }
            interval-secs 10
            unhealthy-threshold 3
        }
    }
}

Reload the configuration:

# Send SIGHUP to reload
kill -HUP $(pgrep sentinel)

Add TLS

For HTTPS, generate certificates and update the config:

# Generate self-signed cert for testing
openssl req -x509 -newkey rsa:4096 -keyout key.pem -out cert.pem -days 365 -nodes \
  -subj "/CN=localhost"

listeners {
    listener "https" {
        address "0.0.0.0:8443"
        protocol "https"
        tls {
            cert-file "cert.pem"
            key-file "key.pem"
        }
    }
}

Test with:

curl -k https://localhost:8443/

Troubleshooting

“command not found: sentinel”

The install directory isn’t in your PATH. Add it:

# Check where it was installed
ls ~/.local/bin/sentinel || ls /usr/local/bin/sentinel

# Add to PATH (add this to your ~/.bashrc or ~/.zshrc)
export PATH="$HOME/.local/bin:$PATH"

# Reload your shell
source ~/.bashrc  # or source ~/.zshrc

“Permission denied” when installing

The installer needs write access to /usr/local/bin:

# Option 1: Use sudo (will prompt for password)
curl -fsSL https://getsentinel.raskell.io | sudo sh

# Option 2: Install to user directory (no sudo needed)
# The script will automatically fall back to ~/.local/bin

“Address already in use” when starting

Another process is using port 8080:

# Find what's using the port
lsof -i :8080

# Either stop that process, or change Sentinel's port
# In sentinel.kdl, change:
#   address "0.0.0.0:8080"
# to:
#   address "0.0.0.0:9000"

“Connection refused” when testing

Your backend server isn’t running or is on a different port:

# Check if backend is running
curl http://localhost:3000/

# If not, start one for testing
python3 -m http.server 3000

Configuration errors

Validate your config file:

sentinel --config sentinel.kdl --check

Common issues:

  • Missing closing braces }
  • Typos in property names (e.g., adress instead of address)
  • Invalid port numbers (must be 1-65535)

Next Steps