4-health-checks.md

Consul Health Checks

You can't really have useful service discovery without health checking. Consul gives you two ways to register healthchecks:

1. check definition (config) files, and
2. the HTTP API (see the python applications used in this course)

There are a bunch of different kinds of checks types that you can register, depending on what you're checking and how you want to do it:

1. Script
2. HTTP
3. TCP
4. TTL
5. Docker
6. gRPC
7. Alias

Docs: https://www.consul.io/docs/agent/checks.html

Ensure that enable_local_script_checks is turned on in the consul agent config

Check your config!

Register a check with a config file

mkdir -p /etc/consul.d/checks

cat <<EOF > '/etc/consul.d/checks/nginx.json'
{
  "service": {
    "name": "nginx",
    "tags": [
      "web"
    ],
    "port": 80,
    "check": {
      "args": ["curl", "localhost"],
      "interval": "10s"
    }
  }
}
EOF

systemctl reload consul

Test service health

curl 'http://localhost:8500/v1/health/service/web?passing'

dig nginx.service.consul

Make the service unhealthy

Turn off nginx:

systemctl stop nginx

Consul will mark it as unhealthy:

curl 'http://localhost:8500/v1/health/service/web?passing'

dig nginx.service.consul