consul

Consul provides service discovery, health checking, KV storage, and service mesh capabilities.

Installation

# Install Consul
wget -O- https://apt.releases.hashicorp.com/gpg | sudo gpg --dearmor -o /usr/share/keyrings/hashicorp-archive-keyring.gpg
echo "deb [signed-by=/usr/share/keyrings/hashicorp-archive-keyring.gpg] https://apt.releases.hashicorp.com $(lsb_release -cs) main" | sudo tee /etc/apt/sources.list.d/hashicorp.list
sudo apt update && sudo apt install consul

# Start dev agent
consul agent -dev

# Check cluster members
consul members

Server Configuration

# consul-server.hcl — Production Consul server config
datacenter = "dc1"
data_dir   = "/opt/consul/data"
log_level  = "INFO"

server           = true
bootstrap_expect = 3

bind_addr   = "{{ GetPrivateInterfaces | include \"network\" \"10.0.0.0/8\" | attr \"address\" }}"
client_addr = "0.0.0.0"

ui_config { enabled = true }

connect { enabled = true }

addresses {
  http  = "0.0.0.0"
  grpc  = "0.0.0.0"
}

ports {
  grpc = 8502
}

encrypt = "your-gossip-encryption-key"

acl {
  enabled                  = true
  default_policy           = "deny"
  enable_token_persistence = true
}

tls {
  defaults {
    ca_file   = "/opt/consul/tls/ca.pem"
    cert_file = "/opt/consul/tls/server.pem"
    key_file  = "/opt/consul/tls/server-key.pem"
    verify_incoming = true
    verify_outgoing = true
  }
}

autopilot {
  cleanup_dead_servers = true
  last_contact_threshold = "200ms"
  server_stabilization_time = "10s"
}

Service Registration

// services/web.json — Register web service with health check
{
  "service": {
    "name": "web",
    "port": 8080,
    "tags": ["production", "v2"],
    "meta": {
      "version": "2.0.0"
    },
    "check": {
      "http": "http://localhost:8080/health",
      "interval": "10s",
      "timeout": "5s",
      "deregister_critical_service_after": "30m"
    }
  }
}

# Register and query services via CLI
consul services register services/web.json
consul services deregister -id=web

# DNS-based service discovery
dig @127.0.0.1 -p 8600 web.service.consul SRV

# HTTP API service discovery
curl http://localhost:8500/v1/health/service/web?passing=true

# Catalog queries
consul catalog services
consul catalog nodes

KV Store

# Key-value operations
consul kv put config/app/db_host "db.example.com"
consul kv put config/app/db_port "5432"

consul kv get config/app/db_host
consul kv get -recurse config/app/

# Import/export
consul kv export config/ > backup.json
consul kv import @backup.json

# Delete keys
consul kv delete config/app/db_host
consul kv delete -recurse config/app/

# Watch for changes
consul watch -type=key -key=config/app/db_host /scripts/reload.sh

Service Mesh (Connect)

# connect-proxy.hcl — Service with sidecar proxy
service {
  name = "web"
  port = 8080

  connect {
    sidecar_service {
      proxy {
        upstreams {
          destination_name = "api"
          local_bind_port  = 9091
        }
        upstreams {
          destination_name = "database"
          local_bind_port  = 9092
        }
      }
    }
  }
}

# intentions.hcl — Service intentions for access control
Kind = "service-intentions"
Name = "api"
Sources = [
  {
    Name   = "web"
    Action = "allow"
  },
  {
    Name   = "*"
    Action = "deny"
  }
]

# Manage intentions
consul config write intentions.hcl
consul intention list
consul intention check web api

Prepared Queries

# Create prepared query for failover across datacenters
curl -X POST http://localhost:8500/v1/query -d '{
  "Name": "web-query",
  "Service": {
    "Service": "web",
    "Tags": ["production"],
    "Failover": {
      "Datacenters": ["dc2", "dc3"]
    },
    "OnlyPassing": true
  }
}'

ACL Configuration

# Bootstrap ACL system
consul acl bootstrap

# Create policy
consul acl policy create -name "app-read" \
  -rules='service_prefix "web" { policy = "read" } key_prefix "config/app" { policy = "read" }'

# Create token with policy
consul acl token create -description "App token" -policy-name "app-read"

Common Commands

# Cluster management
consul join 10.0.1.10
consul leave
consul operator raft list-peers
consul operator autopilot state

# Snapshots for backup
consul snapshot save backup.snap
consul snapshot restore backup.snap

# Monitor and debug
consul monitor -log-level=debug
consul debug -duration=30s -interval=5s