Consul vs SkyDNS vs etcd: What are the differences?

<Consul, SkyDNS, and etcd are popular tools used for service discovery and configuration management in distributed systems. Each tool has its own unique features and use cases. Below are the key differences between Consul, SkyDNS, and etcd.>

1. **Data Store**: Consul uses a gossip protocol for clustering and uses a key-value store for service registration and discovery, while etcd is a consistent key-value store that uses Raft consensus algorithm. SkyDNS, on the other hand, is a DNS-based service discovery tool that stores service information in DNS records.

2. **Health Checking**: Consul provides built-in health checking capabilities where services can periodically report their health status. In contrast, etcd does not have native health checking functionalities. SkyDNS also lacks built-in health checking but relies on DNS-based service discovery for routing traffic to healthy instances.

3. **Secure Communication**: Consul supports out-of-the-box encryption for securing communication between nodes and clients using TLS. Etcd also offers TLS encryption as an option but requires additional configuration. SkyDNS does not inherently provide security features for communication between services.

4. **Multi-Datacenter Support**: Consul has robust support for multi-datacenter setups, allowing services to be discovered across multiple geographical locations. Etcd, although not designed specifically for multi-datacenter use, can be configured to work across different regions. SkyDNS is more limited in its multi-datacenter capabilities compared to Consul and etcd.

5. **Integration with Other Tools**: Consul provides a rich set of APIs and integrations with popular tools like Prometheus, Grafana, and Kubernetes. Etcd, on the other hand, is often used as a highly available data store for Kubernetes clusters due to its compatibility with Kubernetes API server. SkyDNS, being a DNS-based service discovery tool, can integrate seamlessly with DNS servers and clients.

6. **Consistency Model**: Consul uses eventual consistency for its key-value store, meaning that changes may take some time to propagate across all nodes in the cluster. Etcd, on the other hand, provides strong consistency guarantees due to its Raft consensus algorithm. SkyDNS provides eventual consistency for service discovery records stored in DNS.

In Summary, the key differences between Consul, SkyDNS, and etcd lie in their data store mechanisms, health checking capabilities, secure communication features, multi-datacenter support, integration options, and consistency models.