Consul 1.15 Key Value Store Practice Test 2 — 15 Questions

Question 1

A CI pipeline writes build artifacts metadata under `ci/builds/`. An operator needs to remove the entire `ci/builds/` subtree, including all nested keys, in a single command without affecting `ci/other/`. Which command accomplishes this?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

consul kv delete ci/builds/. Recursive deletion in Consul KV is expressed by ending the key with a slash. That signals the operation to apply to the whole subtree rather than a single literal key. Using a trailing slash on the intended prefix removes all build metadata while preserving unrelated sibling paths under the same parent.

Answer

consul kv put ci/builds/ --empty

Answer

consul kv delete -recurse ci/builds/

Answer

consul kv delete ci

Question 2

You are using Consul KV to store feature flags for a distributed application. You need to perform a transaction that atomically updates two keys: one to enable a feature and another to set its rollout percentage. Which two Consul KV operations can be combined in a single transaction to achieve this? (Choose two.)

Accepted Answer

Set a key to a new value.. The transaction API supports set, delete, and check-and-set operations. To atomically update two keys, you would use set operations for each key, optionally with check-and-set to ensure consistency. The two correct operations are set and check-and-set. Delete and lock acquisition are not appropriate for updating values, and index checking is not a transaction operation.

Answer

Check the index of a key.

Answer

Acquire a lock on the key.

Answer

Delete a key.

Question 3

You are using the Consul KV store to coordinate a rolling deployment. A service instance acquires a lock on the key 'deploy/lock' with a session that has a TTL of 30 seconds. The instance crashes, but the Consul agent on that node remains healthy and continues to send TTL renewals because the application process that owned the session was separate from the agent. What will happen to the lock?

Accepted Answer

The lock will remain held indefinitely because the session TTL is renewed by the Consul agent, which is still healthy.. Session TTLs are renewed by the Consul agent, not by the application that created the session. If the agent is healthy, it continues to renew the session, keeping the lock held even if the application crashes. The lock is only released when the session is destroyed, the TTL expires because the agent fails to renew, or the node is marked failed by health checks.

Answer

The lock will be released immediately because Consul detects that the process holding the session is no longer running.

Answer

The lock will be released after the key's default TTL of 15 seconds, regardless of the session TTL.

Answer

The lock will be released after the session TTL expires because the agent stops renewing the session when the application process exits.

Question 4

You are designing a system that uses Consul KV to store configuration data. You need to ensure that reads are highly available and can tolerate stale data, while writes must be strongly consistent. Which TWO of the following statements are true regarding Consul's consistency modes for KV operations? (Choose two.)

Accepted Answer

The 'consistent' consistency mode requires a read to be served by the leader and ensures the most up-to-date data.. Consul offers consistency modes for reads: 'default' (leader-forwarded), 'stale' (any server, may be outdated), and 'consistent' (leader, strongly consistent). The 'stale' mode allows reads from any server, improving availability but potentially returning stale data. The 'consistent' mode ensures reads are served by the leader for up-to-date data. Writes are always strongly consistent and do not have a consistency mode parameter.

Answer

Writes in Consul KV are always eventually consistent and may be lost if a server fails.

Answer

The 'default' consistency mode allows reads to be served by any server, which may be slightly stale.

Answer

The 'stale' consistency mode cannot be used for writes, only for reads.

Question 5

A service reads a KV key that holds a leader-election lock value and must never receive data older than its previous read, even if that means contacting the leader over extra network hops. Which read behavior should the operator request from the KV API?

Accepted Answer

Perform the read with linearizable semantics against the leader.. When a stale lock value could trigger incorrect coordination, the read must be linearizable. Consul's linearizable mode makes the leader verify its standing with a quorum of followers before serving the response, ensuring the value includes every committed write. Default and consistent modes can return data from a leader that has already lost leadership, and stale reads can lag arbitrarily.

Answer

Set the `stale` query parameter to allow the nearest server to answer.

Answer

Set the `stale` parameter to false and rely on the default read mode.

Answer

Target the `/v1/kv/` path on a client agent with `?consistent`.

Question 6

A Consul operator is using the KV store to store feature flags. They notice that after updating a key with `consul kv put feature/new-ui true`, some Consul agents return the old value `false` for a short period. They need to ensure that all reads reflect the latest write immediately. Which consistency mode should they use when reading the key?

Accepted Answer

consistent. To guarantee that reads reflect the latest write, the `consistent` mode must be used. It routes the read to the leader, which has the most up-to-date committed data. The `stale` mode may return old data from followers, and `default` does not guarantee freshness. `leader` is not a valid mode.

Answer

leader

Answer

default

Answer

stale

Question 7

You are designing a system that uses Consul KV to store feature flags. You need to ensure that when a key is updated, all watchers receive the new value with minimal delay, and that the update is visible to all Consul servers before any watcher reads it. Which Consul KV write consistency mode should you use?

Accepted Answer

consistent. For writes, Consul always uses strong consistency by default, but the consistent mode explicitly forces the operation to be handled by the leader. This ensures that the write is committed and replicated to a quorum before returning. Watchers that also use consistent reads will see the update immediately. Stale reads could return old data, and eventual consistency is not a Consul mode.

Answer

stale

Answer

eventual

Answer

default

Question 8

You need to store a binary value in Consul KV using the CLI. The value is a small PNG image. Which command correctly stores the file 'logo.png' under the key 'images/logo'?

Accepted Answer

consul kv put images/logo < logo.png. To store a binary file in Consul KV via the CLI, use 'consul kv put <key>' and redirect the file to stdin. The CLI reads from stdin when no value is given, storing the raw bytes. This approach avoids shell interpretation and preserves binary data integrity, making it suitable for images or other non-text files.

Answer

consul kv put images/logo @logo.png

Answer

consul kv put images/logo "$(cat logo.png)"

Answer

consul kv put images/logo - < logo.png

Question 9

You need to store a configuration value in Consul KV that will be read by multiple services. The value is a JSON object. Which Consul KV CLI command should you use to store this value from a file?

Accepted Answer

cat config.json | consul kv put config/service. The consul kv put command accepts a value either as a command-line argument or from standard input. To store the contents of a file, you can pipe the file into the command using cat or redirect stdin. The correct syntax is to use stdin redirection or piping, as there is no dedicated flag for file input in the Consul KV CLI.

Answer

consul kv put config/service -input=config.json

Answer

consul kv put config/service -file=config.json

Answer

consul kv put config/service @config.json

Question 10

An application uses Consul sessions to hold a lock on the KV key `locks/primary` and must ensure the lock is released if the holder dies. Which two behaviors correctly describe how Consul sessions interact with that KV lock? (Choose two.)

Accepted Answer

A session that is invalidated by its TTL expiring causes any keys acquired with that session to be released.. Session-based KV locks rely on TTL-driven invalidation. A client renews its session before the TTL elapses; if it fails, Consul invalidates the session and frees every lock it held, deleting the lock keys so others can acquire them. Acquire preserves the stored value, and a held lock cannot be taken by another session until release or invalidation occurs.

Answer

A second session can acquire a lock that is already held by forcing a release with a CAS write.

Answer

Acquiring a lock on a key with a session deletes the key's value and stores only the session ID.

Answer

The lock is released only when the holder explicitly calls the release endpoint or CLI release command.

Question 11

You are using Consul KV to store feature flags. You want to ensure that when a client reads a key, it gets the most up-to-date value, even if it means a slightly higher latency. Which consistency mode should the client use when querying the KV store?

Accepted Answer

consistent. Consul KV supports three consistency modes: default, stale, and consistent. Default allows stale reads, stale explicitly allows any server, and consistent forces the read to go through the leader. To ensure the most up-to-date value, the client should use consistent mode, which guarantees linearizability by serving the read from the leader.

Answer

default

Answer

leader

Answer

stale

Question 12

You are using Consul KV to store dynamic configuration for a service. You want to receive notifications whenever a specific key changes, so that the service can reload its configuration. You decide to use Consul's blocking queries. Which parameter must you include in your HTTP GET request to the KV endpoint to implement a blocking query?

Accepted Answer

index. To implement a blocking query, you must include the index parameter in your request, set to the ModifyIndex from a previous response. Consul will then wait until the key's ModifyIndex exceeds that value or the wait time expires. The wait parameter controls the timeout but does not itself enable blocking. Other parameters like recurse and stale serve different purposes.

Answer

wait

Answer

recurse

Answer

stale

Question 13

You are using the Consul CLI to manage KV data. You want to create a new key named 'config/db/host' with the value 'db.example.com'. Which command should you run?

Accepted Answer

consul kv put config/db/host db.example.com. The Consul CLI uses 'consul kv put' to write a value to a key. This command creates the key if it does not exist or updates it if it does. The other options are not valid Consul KV subcommands and would result in errors. The correct syntax is 'consul kv put '.

Answer

consul kv set config/db/host db.example.com

Answer

consul kv create config/db/host db.example.com

Answer

consul kv write config/db/host db.example.com

Question 14

You are managing a Consul KV store and need to perform operations that involve sessions. Which two of the following statements are true regarding Consul sessions and their interaction with the KV store? (Choose two.)

Accepted Answer

A session must be created before it can be used to acquire a lock on a KV key.. Consul sessions are used for distributed locking. A session must exist before a lock can be acquired, and when a session is invalidated, all locks are released. These two statements are true. The other statements are false: locks are exclusive, the minimum TTL is 10 seconds (not 60), and sessions can be created via CLI as well as API.

Answer

Sessions can only be created via the HTTP API, not the CLI.

Answer

A KV key can be locked by multiple sessions simultaneously.

Answer

Session TTL must be at least 10 seconds.

Question 15

A developer writes application configuration to `config/web/db_url` and wants the application to block until that key's value changes rather than polling every second. The application must receive the new value and the index at which the change occurred, and it should wait up to five minutes for a change. Which request satisfies this requirement?

Accepted Answer

A `GET` to `/v1/kv/config/web/db_url?index=<lastIndex>&wait=5m` using the key's previous `ModifyIndex` as `index`.. Consul blocking queries require the client to pass the last observed index in the `index` parameter; the server then holds the request until the underlying data's index exceeds that value or the `wait` time expires. The response includes the new value and its `ModifyIndex`, letting the client update its stored index and reissue the query. This is the mechanism behind long-polling watches and the `watch` command.

Answer

A `GET` to `/v1/kv/config/web/db_url?recurse&wait=5m` using the key's previous `ModifyIndex` as a query string value.

Answer

A `GET` to `/v1/kv/config/web/db_url?consistent&wait=5m` with no `index` parameter.

Answer

A `GET` to `/v1/kv/config/web/db_url?stale&index=0&wait=5m` to register a persistent watch on the key.