Consul 1.15 Service Discovery — 10 Questions

Question 1

You are troubleshooting why a service registered via HTTP API is not showing up in the catalog. Which tool provides the most immediate insight into the registration status?

Accepted Answer

consul catalog services. The 'consul catalog' CLI command allows direct inspection of the catalog state.

Answer

consul kv get

Answer

consul reload

Answer

consul members

Question 2

Which Consul feature allows you to perform health checks against a service that does not have an exposed HTTP endpoint but resides on the same machine?

Accepted Answer

Script health check.. Script-based checks run locally on the agent node, allowing monitoring of processes or system resources.

Answer

TCP health check.

Answer

HTTP health check.

Answer

gRPC health check.

Question 3

An administrator wants to register a service using a JSON file. Where should this file be placed on a standard Consul agent installation to ensure automatic loading?

Accepted Answer

/etc/consul.d/. The Consul agent watches the directory defined by the '-config-dir' flag.

Answer

/var/lib/consul/

Answer

/etc/consul/

Answer

/usr/local/bin/

Question 4

You need to register a service that runs on a dynamic port. How should the service definition be configured to allow Consul to detect the port?

Accepted Answer

Set 'port' to 0 in the service definition.. Consul allows the use of 0 as a port, and the registration process typically involves discovering the port via an external process or environment variable.

Answer

Set 'port' to 'auto' in the service definition.

Answer

Omit the 'port' field entirely.

Answer

Use the 'address' field for the port.

Question 5

You have a service that requires specific routing logic based on the environment. How can you distinguish between 'production' and 'staging' instances of the same service name using metadata?

Accepted Answer

Apply 'production' or 'staging' tags to the service definition.. Service tags are the standard way to categorize and filter services within the Consul catalog.

Answer

Use different service names for every environment.

Answer

Modify the service's port number.

Answer

Assign different Consul datacenters.

Question 6

An administrator needs to query service information. Which DNS record type is commonly used by Consul to return service addresses?

Accepted Answer

SRV. Consul maps service names to SRV or A records for discovery.

Answer

TXT

Answer

MX

Answer

CNAME

Question 7

A service is intermittently failing to resolve via DNS because it has multiple health checks, some of which are 'warning'. How do you ensure it is only returned when all checks are 'passing'?

Accepted Answer

Use the 'passing' query parameter in the DNS request.. Consul DNS returns services if they are not in a 'critical' state by default; enforcing strict 'passing' requires query parameters.

Answer

Configure 'service_prefix' in DNS settings.

Answer

Use the 'stale' query parameter.

Answer

Set 'enable_tag_override' to true.

Question 8

You need to ensure that a service is only discoverable via DNS if it passes its health checks. Which configuration setting in the service definition achieves this?

Accepted Answer

Set the 'passing' parameter to true in the DNS query.. Consul allows filtering services based on health checks via the 'passing' parameter in the DNS interface or by defining the service with a health check.

Answer

Enable 'only_passing' in the DNS configuration.

Answer

Disable the agent's 'allow_stale' read setting.

Answer

Set 'deregister_critical_service_after' to 0.

Question 9

What is the purpose of the 'service-tag' in a Consul service definition?

Accepted Answer

To provide additional categorization or versioning for services.. Tags are used for filtering and identifying specific instances or versions of a service.

Answer

To define the physical location of the server.

Answer

To set the priority of the service in DNS.

Answer

To encrypt communication between services.

Question 10

When using Consul DNS for a service, what happens if no instances are healthy?

Accepted Answer

It returns an empty response (NXDOMAIN or empty set).. By default, if no healthy instances are found, the DNS query will return no results.

Answer

It returns a 500 error.

Answer

It redirects to a standby service.

Answer

It returns all instances regardless of health.