Consul is a distributed service discovery and configuration management system developed by HashiCorp. It provides service registration and discovery, health checking, key-value storage, multi-datacenter support, and other features.
Core Architecture
Consul adopts a decentralized architecture where each node runs a Consul agent. Agents can run in two modes:
- Server Mode: Participates in Raft consensus algorithm, maintains cluster state, handles write requests
- Client Mode: Lightweight proxy that forwards requests to servers and executes health checks
Main Components
- Agent: Process running on each node, responsible for service registration, health checks, etc.
- Server: Server nodes participating in Raft consensus, typically 3-5 nodes form a cluster
- Client: Client proxy that doesn't participate in consensus, only forwards requests
- Datacenter: Datacenter concept supporting cross-datacenter communication
Service Discovery Mechanism
Consul uses DNS or HTTP API for service discovery:
- DNS Interface: Query service addresses via DNS, such as
service.service.consul - HTTP API: Provides RESTful API for service queries
- Health Check: Periodically checks health status of service instances
Consensus Protocol
Consul uses Raft protocol to ensure data consistency:
- Leader election mechanism
- Log replication
- Guarantees strong consistency for read and write operations
Key-Value Storage
Provides distributed key-value storage functionality, supporting:
- Dynamic configuration management
- Service coordination
- Leader election
- Distributed locks
Multi-Datacenter Support
Consul natively supports multi-datacenter deployment:
- WAN gossip protocol connects datacenters
- Cross-datacenter service discovery
- Failover and disaster recovery
Security Features
- TLS encrypted communication
- ACL access control lists
- Gossip protocol encryption
- Secure service-to-service communication
Consul is widely used in microservice architectures, particularly suitable for scenarios requiring service discovery, configuration management, and health checking.