Consul 1.15 Health Checking — 20 Questions

Question 1

Which of the following parameters are used in a service health check configuration? (Select THREE)

Accepted Answer

interval. Interval, timeout, and script/http are standard parameters in check definitions.

Answer

weight

Answer

service_id

Question 2

An operator observes that a service is failing its HTTP health check because the application takes 15 seconds to start up, exceeding the default timeout. Which parameter should be adjusted in the service definition to prevent premature failure?

Accepted Answer

Timeout. The 'timeout' parameter defines how long the agent waits for a response; increasing it allows the service time to initialize.

Answer

InitialStatus

Answer

Interval

Answer

DeregisterCriticalServiceAfter

Question 3

You are monitoring service health using Consul and want to ensure that a service is automatically removed from the catalog if it remains in a 'critical' state for more than 24 hours. Which configuration key supports this?

Accepted Answer

deregister_critical_service_after. The 'deregister_critical_service_after' parameter specifies the threshold after which a service in a critical state is automatically deregistered.

Answer

cleanup_interval

Answer

critical_timeout

Answer

remove_service_after

Question 4

Which agent configuration allows you to specify the local address that the Consul agent binds to for performing health checks?

Accepted Answer

bind_addr. The 'bind_addr' configuration defines the address the agent binds to, which is used for health check traffic initiated by that agent.

Answer

advertise_addr

Answer

client_addr

Answer

check_addr

Question 5

A service has a TTL check configured with a 30-second TTL. If the application crashes and stops sending heartbeats, when will the service status change to 'critical'?

Accepted Answer

After 30 seconds. Consul marks a TTL check as critical if the heartbeat is not received within the specified TTL duration.

Answer

After 60 seconds

Answer

Once the agent restarts

Answer

Immediately

Question 6

When defining a TCP health check, what is the primary indicator that the check is 'passing'?

Accepted Answer

The agent receives a successful TCP handshake. A TCP check is considered passing if the Consul agent can successfully establish a TCP connection to the specified port.

Answer

The port is listed in netstat

Answer

The service responds with a specific string

Answer

The service returns a 200 OK

Question 7

You have configured a Script health check that executes a shell command. For security reasons, you want to restrict which scripts the Consul agent can run. What configuration setting must be set to 'false' in the agent configuration to disable script checks entirely?

Accepted Answer

enable_script_checks. The 'enable_script_checks' configuration parameter must be set to false to prevent the agent from executing scripts defined in configuration files.

Answer

allow_unprivileged_scripts

Answer

disable_remote_exec

Answer

enable_local_script_execution

Question 8

Which HTTP status code range does Consul interpret as a passing state for an HTTP health check?

Accepted Answer

2xx. Consul considers any 2xx status code as a passing health check. Codes 4xx and 5xx result in a critical state.

Answer

3xx

Answer

Any code less than 500

Answer

1xx

Question 9

You are deploying a legacy application that does not support HTTP or TCP health checks. Which Consul health check type should you configure to allow the application to signal its own health via a heartbeat API call?

Accepted Answer

TTL check. The TTL (Time-To-Live) check requires the application to actively report its health status to the Consul agent, making it the correct choice for applications that cannot be polled externally.

Answer

HTTP check

Answer

TCP check

Answer

Script check

Question 10

Which configuration file format is preferred by Consul for defining service health checks?

Accepted Answer

JSON. Consul supports both JSON and HCL, but JSON is the most common format for service definitions.

Answer

XML

Answer

INI

Answer

YAML

Question 11

Which command line tool can you use to manually trigger a TTL check update for a specific service?

Accepted Answer

curl -X PUT http://localhost:8500/v1/agent/check/pass/checkID. The 'consul monitor' is for logs, but to update a check via CLI, one typically interacts with the HTTP API or uses the 'consul kv' command if applicable, but specifically for TTL, the HTTP API endpoint '/v1/agent/check/pass' is the standard method.

Answer

consul kv put

Answer

consul agent -check-update

Answer

consul health update

Question 12

What is the recommended approach for running health checks on a service that is part of a non-containerized, multi-process architecture?

Accepted Answer

Run one check per service definition. Defining separate health checks for each process or a single composite check that monitors the aggregate health is the standard practice.

Answer

Only check the parent process

Answer

Use only TCP checks

Answer

Use a single script check that kills the service

Question 13

You are using Consul Template to observe health status. What happens to a service's health check status if the network segment between the agent and the server is partitioned and the server cannot contact the agent?

Accepted Answer

It enters a critical state. If a server cannot reach the agent performing the check, the health status becomes unknown or unreachable, often reflected as a critical status for the service until connectivity is restored.

Answer

It is automatically removed from the catalog

Answer

It remains passing

Answer

It stays in the last known state

Question 14

When configuring a Service-specific health check, what is the impact of setting the 'expose' field to true?

Accepted Answer

The check status is exposed on the HTTP interface. Setting 'expose' to true allows the service to expose its health checks via the local agent's HTTP interface, enabling external access to the health check status.

Answer

The service is automatically registered with a Load Balancer

Answer

The check is bypassed

Answer

The agent automatically upgrades the check to HTTP

Question 15

Which status indicates that a health check is successfully passing according to Consul?

Accepted Answer

passing. The status 'passing' represents a healthy check in Consul.

Answer

unknown

Answer

critical

Answer

warning

Question 16

What is the purpose of the 'check' field inside a 'service' object in a Consul configuration file?

Accepted Answer

To define the health status requirements. The 'check' field is used to define health checks specifically associated with the service instance, ensuring the service is marked critical if the check fails.

Answer

To provide credentials for the service

Answer

To enable service discovery

Answer

To set the service weight

Question 17

When a health check is failing, which Consul API endpoint would you call to investigate the specific error message provided by the check?

Accepted Answer

/v1/health/checks/. The '/v1/health/checks/' endpoint provides detailed information about the status and output of checks for a given service.

Answer

/v1/agent/services

Answer

/v1/agent/self

Answer

/v1/catalog/nodes

Question 18

Which of the following is a valid method to update a TTL health check?

Accepted Answer

HTTP PUT to the /agent/check/pass endpoint. The agent exposes an HTTP API endpoint to update the status of a TTL check manually.

Answer

Using the 'consul kv' update

Answer

Consul CLI 'health' command

Answer

Editing the service definition file

Question 19

In a Consul health check, what does the 'notes' field provide?

Accepted Answer

A human-readable description. The 'notes' field allows operators to add human-readable descriptions of what the health check monitors.

Answer

The trigger time

Answer

The expected result

Answer

The logic for the check

Question 20

You want to run a shell command as a health check. Which field in the service definition specifies the command to execute?

Accepted Answer

script. The 'args' or 'script' field is used to define the command the Consul agent executes to perform a script check.

Answer

check_exec

Answer

command

Answer

action