KodeKloud Notes

In this section, we reviewed the essential steps to install, configure, and operate Consul agents in both server and client modes.

Key Takeaways

Task	Description	Example/Command
Agent Startup	Launch Consul from the CLI or via a JSON/HCL config file	`consul agent -dev -bind 192.168.1.10`
Configuration Formats	Define common settings, server/client roles, and register services	HCL or JSON snippets
Network Binding & Ports	Set `bind_addr`, and customize RPC, HTTP, and DNS port assignments	`bind_addr = "0.0.0.0"`
Cluster Join & Leave	Add nodes with `consul join` and gracefully remove them using `consul leave`	`consul join 10.0.0.1`

Note

Before restarting agents, validate your configuration:

consul validate /path/to/config.hcl

1. Starting and Managing the Consul Process

You can start a Consul agent directly from the command line:

consul agent \
  -dev \
  -bind 192.168.1.10 \
  -config-dir /etc/consul.d

Or use an HCL/JSON configuration file (consul.hcl):

datacenter       = "dc1"
node_name        = "consul-server-1"
server           = true
bootstrap_expect = 3
bind_addr        = "0.0.0.0"

ports {
  http = 8500
  rpc  = 8400
  dns  = 8600
}

2. Interpreting Consul Agent Configurations

Both HCL and JSON support the same agent options.
Example HCL for a client agent registering a web service:

service {
  name = "web"
  port = 80
  tags = ["nginx", "frontend"]
}

3. Configuring Network Addresses and Ports

Fine-tune Consul network settings to optimize performance and security:

bind_addr: IP/interface for RPC, HTTP, DNS
advertise_addr: Publicly advertised address
ports.rpc, ports.http, ports.dns

bind_addr = "10.0.0.5"
advertise_addr = "203.0.113.10"

ports {
  http = 8500
  rpc  = 8400
  dns  = 8600
}

4. Agent Join and Leave Behaviors

Joining a Cluster

Use the consul join command to add a new node:

consul join 10.0.0.1 10.0.0.2

Graceful Leave

For clients and especially servers, remove nodes gracefully to maintain cluster health:

consul leave

Warning

Always drain and remove server nodes gracefully to avoid quorum loss.
Use consul leave rather than killing the process.

Next Steps

Move on to Objective 3: Service Discovery & Health Checking to learn how Consul automatically tracks and verifies service health.

Links and References

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