Consul 1.15 Practice Questions 2 — 50 Questions

Question 1

Which protocol do Consul servers use to maintain the WAN gossip pool?

Accepted Answer

Serf (SWIM). Consul uses the Serf library, which implements the SWIM-based gossip protocol for both LAN and WAN communication.

Answer

gRPC

Answer

DNS

Answer

HTTP

Question 2

When joining a new datacenter to an existing WAN pool, what is the best practice for server versions?

Accepted Answer

Versions should be consistent across all datacenters.. Running different versions of Consul is supported during upgrades, but maintaining consistent versions across the federation is recommended for stability.

Answer

The new DC must run a newer version.

Answer

The new DC must run an older version.

Answer

Version doesn't matter at all.

Question 3

Which Consul agent configuration parameter defines the KV store file location when running locally?

Accepted Answer

data_dir. While the KV store is in-memory, its persistence (if snapshots are used) is managed by the data_dir.

Answer

server_dir

Answer

kv_dir

Answer

state_dir

Question 4

You want to perform a list operation on a KV prefix to see all keys, but you don't want the values returned. Which API parameter helps reduce payload size?

Accepted Answer

keys=true. The 'keys' parameter can be used with a prefix to return only the list of key names, not their contents.

Answer

raw=true

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list=true

Answer

summarize=true

Question 5

Which TWO of the following are true regarding the behavior of the Consul KV store?

Accepted Answer

Stale reads allow for reading from non-leader nodes. KV values are stored as base64 encoded strings in the API, and they are eventually consistent for stale reads.

Answer

Keys can only contain alphanumeric characters

Answer

All KV writes are synchronous across all nodes

Answer

The KV store is limited to 1GB of data

Question 6

You have enabled ACL replication between a primary and secondary datacenter. What is the effect of changing an ACL policy in the primary datacenter?

Accepted Answer

The changes are asynchronously replicated to all secondary datacenters.. ACL replication automatically propagates changes from the primary to secondary datacenters to maintain consistency.

Answer

The changes only propagate if the secondary is in maintenance mode.

Answer

The changes require a manual trigger on secondary servers.

Answer

The changes are ignored by secondary datacenters.

Question 7

Which TWO of the following are common use cases for the Consul KV store?

Accepted Answer

Distributed locking. KV is primarily used for configuration management and distributed locking.

Answer

Traffic routing

Answer

Service discovery

Answer

Running custom scripts

Question 8

Which TWO statements are true regarding Consul Mesh Gateways?

Accepted Answer

They are required when direct WAN gossip is not possible between datacenters.. Mesh gateways function at Layer 7 and are essential for connectivity between isolated datacenters.

Answer

They replace the need for Consul servers in the secondary datacenter.

Answer

They increase the latency of LAN gossip.

Answer

They require a separate Consul Enterprise license.

Question 9

Which TWO of the following are valid ways to troubleshoot inter-datacenter communication issues?

Accepted Answer

Inspect server logs for RPC errors between datacenters.. Verifying WAN gossip members and checking server logs for RPC errors are standard troubleshooting steps.

Answer

Change the datacenter name in the config.

Answer

Restart all clients in the datacenter.

Answer

Use 'consul kv export' to sync data.

Question 10

Which THREE of the following are true about Consul KV keys?

Accepted Answer

Keys support storing binary data. Keys are organized in a hierarchy, they are case-sensitive, and they can store arbitrary data.

Answer

Keys must start with a slash

Answer

Keys cannot contain spaces

Question 11

What happens to the gossip protocol if the 'encrypt' key is mismatched between two datacenters trying to join via WAN?

Accepted Answer

The join fails.. If the encryption keys do not match, the agents will be unable to decrypt the gossip packets and the join will fail.

Answer

The join proceeds with warnings.

Answer

The connection defaults to unencrypted.

Answer

Only metadata is encrypted.

Question 12

How do you enable WAN federation between two Consul datacenters that do not share a network?

Accepted Answer

By deploying Mesh Gateways.. Mesh gateways allow cross-datacenter communication in environments where direct WAN gossip is not possible.

Answer

By disabling ACLs.

Answer

By increasing the gossip interval.

Answer

By using a load balancer in front of the servers.

Question 13

Which THREE items are required when configuring ACL replication in Consul?

Accepted Answer

The 'acl_replication' configuration block enabled.. ACL replication needs a defined primary, a valid token for reading, and the enabled replication flag.

Answer

A global root ACL token on every client node.

Answer

The 'raft_protocol' version set to 1.

Question 14

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.. Consul removes the service instance from DNS results when its health check is critical.

Answer

It marks the record as 'stale'.

Answer

It returns the IP but with a low TTL.

Answer

It returns a 503 status code.

Question 15

What is the role of a Consul server in a non-primary datacenter regarding ACLs?

Accepted Answer

They replicate the ACL state from the primary.. Secondary servers in an ACL-replicated setup act as a read-only mirror of the primary's ACL policy set.

Answer

They ignore all ACLs.

Answer

They can write new ACL policies independently.

Answer

They become the primary if the original primary fails.

Question 16

To verify if two datacenters are connected via WAN, which command shows the remote datacenter's server nodes?

Accepted Answer

consul members -wan. The 'consul members -wan' command lists all nodes participating in the WAN gossip pool, regardless of their local datacenter.

Answer

consul members

Answer

consul info

Answer

consul operator raft list-peers

Question 17

Which THREE factors influence cross-datacenter service discovery resolution?

Accepted Answer

The local server must have knowledge of the remote datacenter's server addresses.. Resolution depends on the ability to query the remote DC, the health status of the remote instances, and the configuration of the local discovery agent.

Answer

All services must be in the same namespace.

Answer

The local agent must have superuser permissions.

Question 18

You are joining two Consul datacenters via WAN gossip. Which command must be executed on a Consul server in the secondary datacenter to initiate the federation?

Accepted Answer

consul join -wan <remote-server-address>. The consul join command with the -wan flag is the standard mechanism to introduce a node from one datacenter into the WAN gossip pool of another.

Answer

consul members -wan

Answer

consul reload -wan

Answer

consul agent -join-wan

Question 19

Which TWO of the following describe a Consul 'service definition'?

Accepted Answer

A configuration that the agent watches for changes.. They are JSON/HCL files and are monitored by the agent.

Answer

A database-specific configuration.

Answer

A static, immutable file.

Answer

A binary file loaded into the server.

Question 20

A service in datacenter A needs to call a service in datacenter B. If 'prepared_queries' are not used, how does the service discovery query look?

Accepted Answer

.service..consul. When not using prepared queries, standard DNS discovery across DCs follows the pattern .service..consul.

Answer

<service>.service.consul

Answer

..service.consul

Answer

remote.<service>.service.consul