Consul 1.15 Health Checking Practice Test 3 — 15 Questions

Question 1

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. A TTL check in Consul marks the service as critical when the TTL interval elapses without a heartbeat update. Since the TTL is set to 30 seconds, the check will transition to critical exactly 30 seconds after the last successful heartbeat. The application crashing means no further heartbeats are sent, so the timer expires and Consul updates the service status to critical.

Answer

After 60 seconds

Answer

Once the agent restarts

Answer

Immediately

Question 2

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. For a TCP health check, Consul considers the check passing if it can successfully establish a TCP connection to the specified port. This is indicated by a successful TCP handshake (SYN, SYN-ACK, ACK). No application-level response is required.

Answer

The port is listed in netstat

Answer

The service responds with a specific string

Answer

The service returns a 200 OK

Question 3

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

Accepted Answer

2xx. Consul's HTTP health check considers the check passing only when the endpoint returns an HTTP status code in the 2xx range (200-299). Any other status — including 3xx redirects — is treated as critical/failing. This strict interpretation ensures the monitored service is actually serving content, not redirecting or erroring.

Answer

3xx

Answer

Any code less than 500

Answer

1xx

Question 4

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. A TTL check is designed exactly for this scenario: the service (or an external script) must periodically call Consul's HTTP API to mark itself healthy, and if the TTL elapses without an update, Consul marks the check critical. This lets a legacy application that cannot expose HTTP/TCP endpoints signal its own health via a heartbeat.

Answer

HTTP check

Answer

TCP check

Answer

Script check

Question 5

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 HTTP API exposes agent check endpoints that allow external systems to push health status updates. A TTL check registered with the local agent can be manually marked passing by sending an HTTP PUT to /v1/agent/check/pass/<checkID> on port 8500. This is the documented mechanism for scripts and external monitors to report liveness without waiting for the TTL to expire.

Answer

consul kv put

Answer

consul agent -check-update

Answer

consul health update

Question 6

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. For a non-containerized, multi-process service, Consul's recommended approach is to define one health check per service definition so each process or component can be independently verified. This gives accurate per-process health visibility and avoids the false 'passing' state that a single coarse check can produce when one subprocess dies while another stays up.

Answer

Only check the parent process

Answer

Use only TCP checks

Answer

Use a single script check that kills the service

Question 7

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 8

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

Accepted Answer

passing. In Consul, a health check status of 'passing' means the check is succeeding — the service is healthy according to that check. This is the positive status that indicates the check's success condition is met, whether it's an HTTP 200, a script exit code 0, or a TTL being renewed.

Answer

unknown

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critical

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warning

Question 9

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. In a Consul service definition, the check field (or checks array) declares one or more health checks associated with that service, such as HTTP, TCP, script, TTL, or gRPC checks. Consul uses these checks to determine whether the service instance is healthy and should be returned by DNS or the catalog API. The correct answer is that it defines the health status requirements for the service.

Answer

To provide credentials for the service

Answer

To enable service discovery

Answer

To set the service weight

Question 10

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 returns the health checks for a given service, including the status and output of each check. This output often contains the specific error message from the check, making it the correct endpoint to investigate a failing health check.

Answer

/v1/agent/services

Answer

/v1/agent/self

Answer

/v1/catalog/nodes

Question 11

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

Accepted Answer

HTTP PUT to the /agent/check/pass endpoint. TTL checks are updated by calling the Consul HTTP API's agent check endpoints — specifically an HTTP PUT to /v1/agent/check/pass/<check_id> (or /warn and /fail) — which resets the TTL timer and marks the check healthy. This is the canonical heartbeat mechanism for TTL checks.

Answer

Using the 'consul kv' update

Answer

Consul CLI 'health' command

Answer

Editing the service definition file

Question 12

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

Accepted Answer

A human-readable description. The 'notes' field in a Consul health check is a free-form, human-readable string that operators use to document the purpose, ownership, or remediation guidance for the check. It is displayed in the Consul UI and API responses but has no effect on the check's pass/fail evaluation. This makes it purely informational metadata for operators and dashboards.

Answer

The trigger time

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The expected result

Answer

The logic for the check

Question 13

What is the primary difference between a 'script' check and an 'http' check in terms of how they are processed by the Consul agent?

Accepted Answer

Script checks require executing a local process. Script checks execute a local command or script on the Consul agent's host, while HTTP checks make an HTTP request to a specified URL. The key processing difference is that script checks spawn a subprocess, which can be resource-intensive and requires the script to be present on the node. HTTP checks are handled internally by the agent's HTTP client without executing external code.

Answer

HTTP checks are more secure

Answer

Only HTTP checks support intervals

Answer

Script checks are faster

Question 14

If a service has multiple health checks associated with it, when is the service itself considered 'critical'?

Accepted Answer

When any check is critical. In Consul, a service is considered 'critical' if any of its associated health checks are in a critical state. This is because the service's overall health is an aggregation where the worst status among all checks determines the service status. Therefore, a single critical check makes the entire service critical.

Answer

When a majority of checks are critical

Answer

When all checks are critical

Answer

Only if the primary check is critical

Question 15

When using the HTTP health check type, how can you verify that a specific header is included in the health check request?

Accepted Answer

By adding the 'header' object to the check definition. In Consul's HTTP health check definition, you can specify custom headers using the 'header' object, which is a map of header names to arrays of values. This allows the health check request to include specific headers required by the application.

Answer

By appending it to the URL string

Answer

It is not possible

Answer

By setting the environment variable