Consul 1.15 Key Value Store — 20 Questions

Question 1

Which TWO of the following are valid ways to interact with the Consul KV store?

Accepted Answer

Consul HTTP API. The HTTP API and the CLI are the two primary supported interfaces for KV interactions.

Answer

Direct file system access to KV data

Answer

SQL queries

Answer

Consul GUI (Web UI)

Question 2

You need to ensure that a value written to the KV store is persisted to disk on a majority of Consul servers before returning. Which parameter affects this?

Accepted Answer

Writes are committed by default via Raft.. Consul's raft protocol handles consistency; writes are only acknowledged after a quorum of servers commits the change to their log. No special parameter is needed as this is default behavior for writes. However, among the choices, understanding that KV writes are Raft-based operations is key.

Answer

sync=true

Answer

consistency=strong

Answer

wait=majority

Question 3

When using the Consul KV store, what is the maximum size allowed for a single value in a key?

Accepted Answer

512 KB. Consul enforces a hard limit of 512 KB per KV entry value.

Answer

There is no limit.

Answer

128 KB

Answer

1 MB

Question 4

An application is using Consul KV to store configuration. You notice that the KV store is becoming large. What is the most efficient way to retrieve only the keys under the prefix "service/web/"?

Accepted Answer

Use the recurse=true parameter in the query string.. The recurse parameter allows the KV API to return all keys with a matching prefix, rather than just the single key specified.

Answer

Set the depth parameter to 1.

Answer

Use the index parameter with value 0.

Answer

Use the keys parameter with the prefix.

Question 5

Which Consul API endpoint is used to create a new session that can be used for locking KV keys?

Accepted Answer

/v1/session/create. The /v1/session/create endpoint is the standard way to initialize a session object in Consul.

Answer

/v1/kv/acquire

Answer

/v1/lock/init

Answer

/v1/session/renew

Question 6

You are configuring a Consul Watch to trigger a script whenever a specific KV key changes. Which type of watch should you define in your configuration file?

Accepted Answer

key. The 'key' watch type is specifically designed to monitor changes to a single KV entry.

Answer

event

Answer

service

Answer

nodes

Question 7

You have implemented a leader election mechanism using Consul KV sessions. The session has a TTL of 15 seconds. If the application crashes, how long will it take for the lock to be automatically released?

Accepted Answer

15 seconds.. When a session has a TTL, the lock is released when the session is invalidated by the health check failure. The default session invalidation is tied to the TTL.

Answer

Immediately.

Answer

60 seconds.

Answer

The lock is never released until manually deleted.

Question 8

You observe that a session lock is being released unexpectedly. What is the most likely cause?

Accepted Answer

The session TTL is too low, causing premature expiration.. If the session TTL is too short, the agent might fail to renew the session in time, causing it to expire.

Answer

The Consul agent is in leader mode.

Answer

The index was not incremented.

Answer

The KV key was deleted.

Question 9

You want to perform a blocking query on a KV key to watch for updates. Which parameter must you provide in your request based on the last observed index?

Accepted Answer

index. The index parameter is used in the query string to inform Consul that you want to wait until the current state index is greater than the provided value.

Answer

consistency

Answer

wait

Answer

timeout

Question 10

You need to perform a write operation to the Consul KV store that only succeeds if the current ModifyIndex of the key is zero. Which parameter should you include in your API call?

Accepted Answer

cas=0. The cas (Check-And-Set) parameter allows for atomic operations. Setting cas to 0 ensures the write only occurs if the key does not already exist.

Answer

acquire=0

Answer

flags=0

Answer

index=0

Question 11

Which command-line interface command is used to set a value in the Consul KV store?

Accepted Answer

consul kv put. The 'consul kv put' command is the standard CLI utility for setting key values.

Answer

consul kv write

Answer

consul kv set

Answer

consul kv update

Question 12

When a session is associated with a lock, what happens to the lock if the session is deleted?

Accepted Answer

The lock is released.. Deleting a session immediately releases any locks associated with that session.

Answer

The lock remains held by the server.

Answer

The lock is held until the key is deleted.

Answer

The lock transfers to a new session.

Question 13

Which flag can be used to pass arbitrary metadata to a KV entry?

Accepted Answer

flags. The 'flags' field in the KV API allows users to store an unsigned integer for application-specific metadata.

Answer

labels

Answer

metadata

Answer

tags

Question 14

Which HTTP method is used to create or update a key in the Consul KV store?

Accepted Answer

PUT. The PUT method is the standard HTTP verb used for key creation and updates in the Consul API.

Answer

GET

Answer

DELETE

Answer

POST

Question 15

You need to ensure that a read operation from the KV store is strongly consistent. Which consistency mode should you specify?

Accepted Answer

consistent. The 'consistent' consistency mode forces the leader to verify its leadership with a quorum of peers, ensuring strong consistency.

Answer

default

Answer

quorum

Answer

stale

Question 16

What is the purpose of the 'Behavior' field when creating a Consul session?

Accepted Answer

To specify what happens to locks on session invalidation.. The behavior field determines what happens to locks when a session is invalidated; 'release' is the default, while 'delete' removes the key.

Answer

To define the node affinity.

Answer

To determine if the session can be renewed.

Answer

To set the session priority.

Question 17

If a Consul agent is configured with 'disable_remote_exec = true', how does this affect the KV store?

Accepted Answer

It has no effect on the KV store.. This setting does not impact the KV store; it only restricts the execution of remote commands via the Consul event system.

Answer

It forces all KV reads to be consistent.

Answer

It prevents all KV writes.

Answer

It disables KV watches.

Question 18

You want to delete a key and all its children in the KV store using the CLI. Which flag should you use?

Accepted Answer

-recurse. The -recurse flag in the CLI allows the delete operation to act on the key and all nested keys.

Answer

-force

Answer

--all

Answer

--cascade

Question 19

You need to retrieve the session information for a specific session ID. Which endpoint should you query?

Accepted Answer

/v1/session/info/:id. The /v1/session/info/:id endpoint returns the details of a specific session.

Answer

/v1/session/read/:id

Answer

/v1/kv/session/:id

Answer

/v1/session/get/:id

Question 20

What is the default value for the Consul KV flags field if not provided during a write?

Accepted Answer

0. The default value for flags is 0.

Answer

1

Answer

null

Answer

-1