Leader Election

An easy-to-use C# implementation of the distributed leader election pattern, leveraging common infrastructure tools like Azure Blob Storage, Redis, and others.

Features

• Async/Await Support: Full async/await pattern support for better performance and scalability
• Comprehensive Error Handling: Robust error handling with retry logic and exponential backoff
• Structured Logging: Integration with Microsoft.Extensions.Logging for observability
• Configuration Options: Flexible configuration through options pattern
• Event-Driven: Leadership change and error events for reactive programming
• Graceful Shutdown: Proper cleanup and resource disposal
• Thread Safety: Thread-safe operations with proper synchronization

Currently Supported Stores

• Redis → LeaderElection.Redis
• FusionCache → LeaderElection.FusionCache
• DistributedCache → LeaderElection.DistributedCache
• Azure Blob Storage (blob leases) → LeaderElection.BlobStorage
• S3 (minio) → LeaderElection.S3
• Postgres → LeaderElection.Postgres

Quick Start

1. Install the Package

dotnet add package LeaderElection
dotnet add package LeaderElection.Redis

2. Configure Services

Look in LeaderElectionTester for a full example.

using LeaderElection.Redis;

var builder = WebApplication.CreateBuilder(args);

// Add Redis connection
builder.Services.AddSingleton<IConnectionMultiplexer>(sp =>
{
    return ConnectionMultiplexer.Connect("localhost:6379");
});

// Add leader election with configuration
builder.Services.AddRedisLeaderElection(settings =>
{
    settings.LockKey = "leader_election_tester";
    settings.LockExpiry = TimeSpan.FromSeconds(30);
    settings.RenewInterval = TimeSpan.FromSeconds(10);
    settings.RetryInterval = TimeSpan.FromSeconds(5);
    settings.MaxRetryAttempts = 3;
    settings.EnableGracefulShutdown = true;
});

3. Use in Your Service

If you execute this program below, you will notice that leadership is automatically transfered across instances once the current leader is killed!

public class MyService : BackgroundService
{
    private readonly ILeaderElection _leaderElection;
    private readonly ILogger<MyService> _logger;

    public MyService(ILeaderElection leaderElection, ILogger<MyService> logger)
    {
        _leaderElection = leaderElection;
        _logger = logger;
    }

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        // Subscribe to events
        _leaderElection.LeadershipChanged += OnLeadershipChanged;
        _leaderElection.ErrorOccurred += OnErrorOccurred;

        try
        {
            // Start leader election
            await _leaderElection.StartAsync(stoppingToken);

            // Run leader tasks
            while (!stoppingToken.IsCancellationRequested)
            {
                await _leaderElection.RunTaskIfLeaderAsync(async () =>
                {
                    _logger.LogInformation("Executing leader task");
                    await DoLeaderWorkAsync();
                }, stoppingToken);

                _logger.LogInformation("Executing normal task");

                await Task.Delay(TimeSpan.FromSeconds(5), stoppingToken);
            }
        }
        finally
        {
            // Cleanup
            _leaderElection.LeadershipChanged -= OnLeadershipChanged;
            _leaderElection.ErrorOccurred -= OnErrorOccurred;
            await _leaderElection.StopAsync(stoppingToken);
        }
    }

    private void OnLeadershipChanged(object? sender, bool isLeader)
    {
        _logger.LogInformation("Leadership changed: {IsLeader}", isLeader);
    }

    private void OnErrorOccurred(object? sender, Exception exception)
    {
        _logger.LogError(exception, "Leader election error");
    }
}

API Reference

Methods

• StartAsync(CancellationToken) - Start the leader election process
• StopAsync(CancellationToken) - Stop the leader election process
• TryAcquireLeadershipAsync(CancellationToken) - Manually attempt to acquire leadership
• RunTaskIfLeaderAsync(Func<Task>, CancellationToken) - Execute a task only if this instance is the leader
• RunTaskIfLeaderAsync(Action, CancellationToken) - Execute a synchronous task only if this instance is the leader

Properties

• IsLeader - Returns true if this instance is currently the leader
• LastLeadershipRenewal - Date/Time of the last accquisition of leadership

Events

• LeadershipChanged - Fired when leadership status changes
• ErrorOccurred - Fired when an error occurs during leader election

Contributing

1. Fork the repository
2. Create a feature branch
3. Make your changes
4. Add tests
5. Submit a pull request

License

MIT License

Copyright (c) 2025 Greg James

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Icon

"Business icon pack leader icon" by mr icons is licensed under CC BY 4.0