Consul 1.15 Service Discovery Practice Test 4 — 15 Questions

Question 1

A service definition includes a 'meta' block. What is the intended use of this block?

Accepted Answer

To define arbitrary key/value metadata for the service.. The 'meta' block in a service definition is used to define arbitrary key/value metadata for the service. This metadata is not used by Consul for routing or health checks but can be used by external tools, for filtering in the UI, or for custom logic in service discovery. It is a flexible way to attach additional information to a service.

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To configure service discovery timeouts.

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To override the default health check interval.

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To store authentication credentials.

Question 2

Which command is used to check the status of a registered service?

Accepted Answer

consul health service. The 'consul health service' command queries the health of all instances of a named service, returning the nodes, their health check statuses, and associated metadata. It is the standard CLI way to inspect whether a registered service is passing its checks and is reachable through the catalog.

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consul check

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consul status

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consul list

Question 3

You need to register a health check that triggers an alert when memory usage is high. Which type of check is most appropriate?

Accepted Answer

Script Check. A Script check runs an arbitrary executable on the Consul client at a defined interval and interprets its exit code (0 = passing, 1 = warning, other = critical), making it the only check type that can inspect local system metrics like memory usage. HTTP, TCP, and gRPC checks only verify reachability or protocol-level responses and cannot read OS-level resource counters.

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gRPC Check

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HTTP Check

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TCP Check

Question 4

When multiple agents are in a cluster, how does Consul ensure that service discovery information is consistent across all nodes?

Accepted Answer

Via the Raft consensus protocol for catalog changes.. Consul uses the Raft consensus protocol to replicate catalog changes across server nodes, ensuring that service discovery information is consistent and fault-tolerant. Raft elects a leader that handles writes and replicates log entries to followers, guaranteeing that all servers converge on the same state. This is how Consul maintains a consistent service catalog across the cluster.

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Using a centralized database like PostgreSQL.

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By polling the leader every second.

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By broadcasting all service updates to every node.

Question 5

Which of the following best describes the 'consul agent -dev' mode in relation to service discovery?

Accepted Answer

It provides a single-node Consul environment for testing.. The 'consul agent -dev' flag starts a single-node Consul agent configured as a server and client in one process, with an in-memory datastore, no persistence, and no cluster join. It is explicitly designed for local development, testing, and demos — not for production — and it still exposes the DNS interface, HTTP API, and service catalog so you can exercise service discovery locally.

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It disables DNS interfaces.

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It forces the service catalog to be stored in Redis.

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It is suitable for production clusters.

Question 6

What is the impact of setting 'enable_tag_override' to true in a service definition?

Accepted Answer

It allows tags to be modified via the API without updating the config file.. Setting 'enable_tag_override' to true in a service definition allows tags to be modified via the API without updating the service's configuration file. This is useful for dynamic tag changes, such as adding a tag for maintenance mode. By default, this is false, meaning tags are managed by the config file and API changes are overwritten on restart.

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It ignores all tags in the catalog.

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It forces all nodes to update their tags.

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It prevents tags from being used in DNS lookups.

Question 7

Which interface would you use to register a service dynamically using standard tools like 'curl'?

Accepted Answer

HTTP API. The HTTP API is the primary programmatic interface for Consul and exposes RESTful endpoints such as PUT /v1/agent/service/register, which can be invoked with standard tools like curl. This makes it the correct choice for dynamically registering a service without using the CLI or configuration files. The DNS interface is read-only for service discovery, and gossip is an internal membership protocol, not a registration mechanism.

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DNS interface

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Gossip protocol

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CLI agent command

Question 8

What is the effect of changing the 'interval' parameter in a service health check?

Accepted Answer

It changes the frequency at which the check runs.. The `interval` parameter in a Consul health check definition controls how often the check is executed — for example, `interval = "10s"` runs the check every 10 seconds. It directly governs the polling frequency of the check script, HTTP endpoint, or TCP probe, and therefore how quickly Consul detects a state change.

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It changes the DNS TTL.

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It changes the weight of the service.

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It changes the timeout of the check.

Question 9

You need to verify if a node has successfully joined the cluster for service discovery. Which tool confirms this?

Accepted Answer

consul members. The `consul members` command queries the gossip protocol (LAN/WAN) and lists all nodes that are currently part of the Consul cluster, showing their status (alive, left, failed) and role. This directly confirms whether a node has successfully joined the cluster, as it relies on the Serf gossip layer that manages cluster membership. Other commands like `consul catalog nodes` query the catalog, which may not reflect real-time membership status if the node is unreachable or has not synced.

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consul catalog nodes

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consul info

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consul services

Question 10

When a service check transitions to 'critical', what does Consul do with the service's DNS entry?

Accepted Answer

It removes the instance from the DNS response.. When a service check transitions to 'critical', Consul's DNS interface automatically removes that service instance from DNS query results. This is because Consul's DNS server only returns instances that are considered healthy (passing checks). The DNS entry for the service as a whole may still exist if other instances are healthy, but the critical instance is excluded. This behavior ensures that clients using DNS for service discovery do not route traffic to unhealthy instances.

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It marks the record as 'stale'.

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It returns the IP but with a low TTL.

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It returns a 503 status code.

Question 11

Which THREE of the following are valid check types in Consul?

Accepted Answer

TCP. Consul supports HTTP, TCP, and Script (external) health checks.

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SSH

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FTP

Question 12

Which THREE of the following are key components of a service definition?

Accepted Answer

Check/Health Check. In a service definition (as used by service discovery/registry tools such as Consul), the Service Name (E) is the fundamental identifier that registers the service and lets other services and DNS/API lookups discover it, so it is a required key component. The Port (D) is also essential because it tells clients and the registry on which TCP/UDP port the service is listening, enabling correct routing and connection. A Check/Health Check (C) is likewise a core part of the definition, since it defines how the registry verifies the instance is healthy (e.g., an HTTP, TCP, or script check with an interval and timeout) and removes unhealthy instances from discovery. By contrast, a Secret Key (A) is a credential/security artifact, not a structural element of a service definition, and a Node BIOS version (B) is hardware/firmware inventory data that has no role in describing or discovering a service.

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Secret Key

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Node BIOS version

Question 13

Which TWO of the following are true regarding the Consul Service Catalog?

Accepted Answer

It provides a unified view of all services in the cluster.. The catalog is replicated via Raft and can be queried via API or DNS.

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It is strictly read-only.

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It is only accessible via the CLI.

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It is stored in the local disk of every agent.

Question 14

Which THREE of the following are valid ways to register a service in Consul?

Accepted Answer

Kubernetes Custom Resource Definitions.. Option A is correct because Consul supports Kubernetes Custom Resource Definitions (CRDs) such as ServiceRegistration (and previously ServiceDefaults/ServiceResolver via CRDs) as a declarative way to register services when running Consul on Kubernetes with the official Helm chart and CRDs enabled. Option B is correct because services can be defined in agent configuration files (HCL or JSON) placed in the agent's config directory, using a service block or services array, and Consul loads them at agent startup or reload. Option C is correct because the Consul HTTP API exposes the endpoint PUT /v1/agent/service/register, which accepts a JSON service definition and registers the service with the local agent. Option D is not valid because Consul stores state in a Raft-replicated log and snapshot files, not in a directly editable database file; modifying internals would corrupt state and is unsupported. Option E is not valid because the Raft log is an internal replicated log managed by the Raft consensus protocol, and manually editing it would break consistency and is not a supported registration method.

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Directly modifying the Consul database file.

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Manual editing of the Raft log.

Question 15

Which TWO of the following are standard DNS records returned by Consul for service discovery?

Accepted Answer

SRV. Consul's DNS interface returns SRV records (option B) to advertise the port and target host of a registered service instance, which is essential because service discovery must convey both the address and the port the service listens on. Consul also returns A records (option C) that map a service name to the IP address(es) of the healthy instances, allowing clients to resolve a service directly to an IP. These two record types are the core of Consul's service discovery responses, with SRV providing host+port and A providing the IPv4 address. The other options are standard DNS record types but are not the service-discovery answers Consul returns for a service lookup: NS (option A) delegates zones to name servers, SOA (option D) holds zone authority metadata, and PTR (option E) is used for reverse DNS lookups.

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NS

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SOA

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PTR