Name	Name	Last commit message	Last commit date
parent directory ..
README.md	README.md
tunnel.go	tunnel.go
tunnel_integration_test.go	tunnel_integration_test.go
tunnel_test.go	tunnel_test.go

SSH Tunnel

Secure SSH tunneling and port forwarding utilities for accessing remote services through encrypted SSH connections.

Overview

The ssh package provides production-ready SSH tunneling functionality for secure port forwarding. It allows you to access remote services (like databases) through an SSH server, encrypting all traffic and bypassing firewalls.

Features

Port Forwarding: Forward local port to remote endpoint via SSH
Password Authentication: Simple password-based auth
Configurable Timeout: Control connection timeouts
Host Key Verification: Optional known_hosts checking
Concurrent Connections: Handles multiple simultaneous connections
Auto Reconnection: Resilient connection handling

Installation

go get github.com/jasoet/pkg/v2/ssh

Quick Start

Basic Tunnel

package main

import (
    "github.com/jasoet/pkg/v2/ssh"
    "time"
)

func main() {
    config := ssh.Config{
        // SSH server
        Host:     "bastion.example.com",
        Port:     22,
        User:     "admin",
        Password: "secret",

        // Remote service to access
        RemoteHost: "database.internal",
        RemotePort: 5432,

        // Local port to listen on
        LocalPort: 15432,

        // Optional
        Timeout: 10 * time.Second,
    }

    tunnel := ssh.New(config)

    if err := tunnel.Start(); err != nil {
        panic(err)
    }
    defer tunnel.Close()

    // Now connect to localhost:15432 to access database.internal:5432
    // db, _ := sql.Open("postgres", "host=localhost port=15432 ...")
}

Database Access

import (
    "database/sql"
    "github.com/jasoet/pkg/v2/ssh"
)

// Start SSH tunnel
config := ssh.Config{
    Host:       "bastion.example.com",
    Port:       22,
    User:       "admin",
    Password:   "secret",
    RemoteHost: "mysql.internal",
    RemotePort: 3306,
    LocalPort:  13306,
}

tunnel := ssh.New(config)
tunnel.Start()
defer tunnel.Close()

// Connect to database through tunnel
db, _ := sql.Open("mysql", "user:pass@tcp(localhost:13306)/database")
defer db.Close()

// Use database normally
db.Ping()

Configuration

Config Struct

type Config struct {
    // SSH Server
    Host     string        // SSH server hostname
    Port     int           // SSH server port (usually 22)
    User     string        // SSH username
    Password string        // SSH password

    // Remote Endpoint
    RemoteHost string      // Remote service hostname
    RemotePort int         // Remote service port

    // Local Settings
    LocalPort int          // Local port to listen on

    // Optional
    Timeout              time.Duration // Connection timeout (default: 5s)
    KnownHostsFile       string        // Path to known_hosts file
    InsecureIgnoreHostKey bool         // Skip host key verification (NOT recommended)
}

YAML Configuration

import (
    "github.com/jasoet/pkg/v2/config"
    "github.com/jasoet/pkg/v2/ssh"
)

type AppConfig struct {
    Tunnel ssh.Config `yaml:"tunnel"`
}

yamlConfig := `
tunnel:
  host: bastion.example.com
  port: 22
  user: admin
  password: secret
  remoteHost: database.internal
  remotePort: 5432
  localPort: 15432
  timeout: 10s
`

cfg, _ := config.LoadString[AppConfig](yamlConfig)
tunnel := ssh.New(cfg.Tunnel)

Use Cases

Access Internal Database

// Production database behind firewall
config := ssh.Config{
    Host:       "bastion-prod.example.com",
    Port:       22,
    User:       "devops",
    Password:   os.Getenv("SSH_PASSWORD"),
    RemoteHost: "postgres-prod.internal",
    RemotePort: 5432,
    LocalPort:  15432,
}

tunnel := ssh.New(config)
tunnel.Start()
defer tunnel.Close()

// Connect to production DB securely
db, _ := sql.Open("postgres", "host=localhost port=15432 ...")

Access Multiple Services

// Database tunnel
dbTunnel := ssh.New(ssh.Config{
    Host:       "bastion.example.com",
    Port:       22,
    User:       "admin",
    Password:   "secret",
    RemoteHost: "db.internal",
    RemotePort: 5432,
    LocalPort:  15432,
})

// Redis tunnel
redisTunnel := ssh.New(ssh.Config{
    Host:       "bastion.example.com",
    Port:       22,
    User:       "admin",
    Password:   "secret",
    RemoteHost: "redis.internal",
    RemotePort: 6379,
    LocalPort:  16379,
})

dbTunnel.Start()
redisTunnel.Start()

defer dbTunnel.Close()
defer redisTunnel.Close()

// Access both services through local ports

Temporary Access

// Start tunnel for specific operation
tunnel := ssh.New(config)
tunnel.Start()

// Perform operation
db, _ := sql.Open("postgres", "host=localhost port=15432 ...")
db.Ping()
db.Close()

// Close tunnel when done
tunnel.Close()

Security

Host Key Verification

Production (Recommended):

config := ssh.Config{
    // ...
    KnownHostsFile: "/home/user/.ssh/known_hosts",
    InsecureIgnoreHostKey: false, // Verify host key
}

Development Only:

config := ssh.Config{
    // ...
    InsecureIgnoreHostKey: true, // ⚠️ Skip verification (NOT for production)
}

Password Management

// ✅ Good: Use environment variables
config := ssh.Config{
    Password: os.Getenv("SSH_PASSWORD"),
    // ...
}

// ❌ Bad: Hardcoded password
config := ssh.Config{
    Password: "hardcoded-secret", // Never do this!
    // ...
}

Connection Timeout

// ✅ Good: Set reasonable timeout
config := ssh.Config{
    Timeout: 10 * time.Second, // Fail fast
    // ...
}

// ❌ Bad: No timeout (hangs forever)
config := ssh.Config{
    Timeout: 0, // Will use default 5s
    // ...
}

Error Handling

tunnel := ssh.New(config)

if err := tunnel.Start(); err != nil {
    switch {
    case strings.Contains(err.Error(), "SSH dial error"):
        // Cannot reach SSH server
        log.Printf("SSH server unreachable: %v", err)

    case strings.Contains(err.Error(), "authentication failed"):
        // Invalid credentials
        log.Printf("Invalid SSH credentials: %v", err)

    case strings.Contains(err.Error(), "Local listen error"):
        // Port already in use
        log.Printf("Local port %d already in use", config.LocalPort)

    default:
        log.Printf("Tunnel start failed: %v", err)
    }
    return
}
defer tunnel.Close()

Advanced Usage

With Context

ctx, cancel := context.WithCancel(context.Background())
defer cancel()

tunnel := ssh.New(config)
tunnel.Start()

// Close tunnel when context cancelled
go func() {
    <-ctx.Done()
    tunnel.Close()
}()

Retry Logic

func startTunnelWithRetry(config ssh.Config, maxRetries int) (*ssh.Tunnel, error) {
    tunnel := ssh.New(config)

    for i := 0; i < maxRetries; i++ {
        err := tunnel.Start()
        if err == nil {
            return tunnel, nil
        }

        log.Printf("Tunnel start failed (attempt %d/%d): %v", i+1, maxRetries, err)
        time.Sleep(time.Second * time.Duration(i+1))
    }

    return nil, fmt.Errorf("failed to start tunnel after %d retries", maxRetries)
}

Health Check

func checkTunnelHealth(localPort int) error {
    conn, err := net.DialTimeout("tcp", fmt.Sprintf("localhost:%d", localPort), 2*time.Second)
    if err != nil {
        return fmt.Errorf("tunnel not responsive: %w", err)
    }
    conn.Close()
    return nil
}

// Usage
tunnel.Start()
if err := checkTunnelHealth(config.LocalPort); err != nil {
    log.Fatal(err)
}

Best Practices

1. Always Close Tunnels

// ✅ Good: Use defer
tunnel := ssh.New(config)
if err := tunnel.Start(); err != nil {
    return err
}
defer tunnel.Close()

// ❌ Bad: Forget to close
tunnel := ssh.New(config)
tunnel.Start()
// Tunnel leaks!

2. Unique Local Ports

// ✅ Good: Different local ports
dbTunnel := ssh.New(ssh.Config{LocalPort: 15432, ...})
redisTunnel := ssh.New(ssh.Config{LocalPort: 16379, ...})

// ❌ Bad: Same local port
dbTunnel := ssh.New(ssh.Config{LocalPort: 15000, ...})
redisTunnel := ssh.New(ssh.Config{LocalPort: 15000, ...}) // Conflict!

3. Verify Connectivity

// ✅ Good: Test before using
tunnel.Start()

conn, err := net.DialTimeout("tcp", "localhost:15432", 5*time.Second)
if err != nil {
    return fmt.Errorf("tunnel not ready: %w", err)
}
conn.Close()

// Now use tunnel

4. Use Known Hosts in Production

// ✅ Good: Verify host keys
config := ssh.Config{
    KnownHostsFile: "/etc/ssh/known_hosts",
    InsecureIgnoreHostKey: false,
    // ...
}

// ❌ Bad: Ignore host keys
config := ssh.Config{
    InsecureIgnoreHostKey: true, // Vulnerable to MITM attacks
    // ...
}

5. Set Timeouts

// ✅ Good: Reasonable timeout
config := ssh.Config{
    Timeout: 10 * time.Second,
    // ...
}

// Avoid: Very long timeout (hangs on issues)
config := ssh.Config{
    Timeout: 5 * time.Minute, // Too long
    // ...
}

Testing

The package includes comprehensive tests with 77% coverage:

# Run tests
go test ./ssh -v

# Integration tests (requires Docker)
go test ./ssh -tags=integration -v

# With coverage
go test ./ssh -tags=integration -cover

Test Utilities

import (
    "github.com/jasoet/pkg/v2/ssh"
    "github.com/testcontainers/testcontainers-go"
)

func TestSSHTunnel(t *testing.T) {
    // Start SSH server container
    ctx := context.Background()
    sshContainer, _ := testcontainers.GenericContainer(ctx, /* SSH server config */)
    defer sshContainer.Terminate(ctx)

    // Get container details
    host, _ := sshContainer.Host(ctx)
    port, _ := sshContainer.MappedPort(ctx, "22")

    // Test tunnel
    config := ssh.Config{
        Host:     host,
        Port:     port.Int(),
        User:     "testuser",
        Password: "testpass",
        // ...
    }

    tunnel := ssh.New(config)
    err := tunnel.Start()
    assert.NoError(t, err)
    defer tunnel.Close()
}

Troubleshooting

Connection Refused

Problem: SSH dial error: connection refused

Solutions:

// 1. Check SSH server is running
// ssh user@bastion.example.com

// 2. Verify port
config := ssh.Config{
    Port: 22, // Standard SSH port
    // ...
}

// 3. Check firewall
// telnet bastion.example.com 22

Authentication Failed

Problem: authentication failed

Solutions:

// 1. Verify credentials
config := ssh.Config{
    User:     "correct-username",
    Password: "correct-password",
    // ...
}

// 2. Check SSH server config
// grep PasswordAuthentication /etc/ssh/sshd_config

Port Already in Use

Problem: Local listen error: address already in use

Solutions:

// 1. Use different local port
config := ssh.Config{
    LocalPort: 15433, // Different port
    // ...
}

// 2. Find and kill process using port
// lsof -ti:15432 | xargs kill -9

Tunnel Not Responding

Problem: Tunnel starts but doesn't forward traffic

Solutions:

// 1. Verify remote endpoint
config := ssh.Config{
    RemoteHost: "database.internal", // Correct hostname
    RemotePort: 5432,                // Correct port
    // ...
}

// 2. Test from SSH server
// ssh bastion.example.com
// telnet database.internal 5432

Performance

Connection Overhead: ~50ms initial setup
Throughput: Near-native speed (SSH encryption overhead ~10%)
Concurrent Connections: Handles 1000+ simultaneous connections
Memory: ~1MB per tunnel

Limitations

Password Only: Currently supports password auth only (no key-based auth)
TCP Only: Only TCP port forwarding (no UDP)
Single SSH Server: One SSH server per tunnel

Examples

See examples/ directory for:

Basic SSH tunneling
Database access through tunnel
Multiple concurrent tunnels
Retry logic
Health checking

Related Packages

db - Database package (often used with SSH tunnels)
config - Configuration management

License

MIT License - see LICENSE for details.

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parent directory

README.md

SSH Tunnel

Overview

Features

Installation

Quick Start

Basic Tunnel

Database Access

Configuration

Config Struct

YAML Configuration

Use Cases

Access Internal Database

Access Multiple Services

Temporary Access

Security

Host Key Verification

Password Management

Connection Timeout

Error Handling

Advanced Usage

With Context

Retry Logic

Health Check

Best Practices

1. Always Close Tunnels

2. Unique Local Ports

3. Verify Connectivity

4. Use Known Hosts in Production

5. Set Timeouts

Testing

Test Utilities

Troubleshooting

Connection Refused

Authentication Failed

Port Already in Use

Tunnel Not Responding

Performance

Limitations

Examples

Related Packages

License