Consul 1.15 · domain
Multi Datacenter Federation
This domain covers Consul multi-datacenter federation: WAN gossip, the primary/secondary datacenter model, token and config replication, prepared query failover, and datacenter-scoped behavior. Questions test whether you understand that datacenters are isolated for most data, how replication is authorized and rotated, and how cross-DC service discovery actually works.
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What to know about Multi Datacenter Federation
Be able to configure and reason about federated datacenters: WAN gossip, primary/secondary replication, token rotation, and prepared query failover. The key point is that most Consul data, including KV, is datacenter-scoped and only specific data replicates.
WAN gossip federation and the primary/secondary datacenter relationship for replication
ACL token replication and config replication between primary and secondary datacenters
Prepared queries with Failover policy targeting a service in another datacenter
Datacenter scoping of the KV store and the 'datacenter' agent configuration field
Watch out for
Common Multi Datacenter Federation exam traps
- ▸Assuming the KV store replicates across datacenters; it does not, so inconsistent KV reads across DCs are expected behavior, not a fault.
- ▸Forgetting that after rotating a replication token in the primary, the new token must be supplied to the secondary for replication to continue.
- ▸Believing prepared query failover is automatic without a Failover policy and healthy targets; the query must be defined with cross-DC failover.
Question index
All Multi Datacenter Federation questions (45)
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You are deploying Consul servers in a new datacenter that will be a secondary in a federated environment. The primary datacenter is already configured with ACLs enabled and replication is working. You need to ensure the new secondary datacenter can replicate ACLs from the primary. Which configuration must be set on the new secondary's servers?
Easy2A cloud engineer is setting up a new Consul 1.15 datacenter that will join an existing WAN federation. The existing datacenter uses a specific gossip encryption key for the WAN pool. Which configuration parameter must be set on the new datacenter's servers to ensure they can participate in WAN gossip?
Easy3An operator is configuring a new Consul datacenter that must be able to resolve services in a remote datacenter using the DNS interface. The remote datacenter is already federated and reachable. Which query format should the operator use to resolve a service named 'web' in the remote datacenter 'dc2'?
Medium4You are troubleshooting a partition between two datacenters. The WAN gossip shows high latency. Which Consul CLI tool provides the best insight into the WAN gossip state?
Hard5When configuring ACL replication, where must the 'acl_replication_token' be defined?
Medium6An operator is configuring a new Consul 1.15 datacenter 'dc3' to join an existing WAN federation with primary datacenter 'dc1'. The operator wants to ensure that dc3 can automatically rejoin the WAN gossip pool after a restart. Which configuration parameter should be set in dc3's server configuration?
Medium7You are configuring a Consul secondary datacenter to replicate ACLs from the primary. You have set 'primary_datacenter' and 'acl_replication_token' on the servers. However, replication is failing. Which of the following is the most likely cause?
Hard8How do you enable WAN federation between two Consul datacenters that do not share a network?
Easy9What is the role of a Consul server in a non-primary datacenter regarding ACLs?
Medium10Which THREE network considerations are vital for Consul WAN federation?
Hard11In a multi-datacenter environment, what happens if the 'primary_datacenter' server cluster becomes unavailable?
Medium12You are deploying a Consul cluster across three datacenters: dc1, dc2, and dc3. Each datacenter has its own LAN gossip pool and they are all joined via WAN gossip. You want to enable cross-datacenter service discovery so that services in dc1 can discover services in dc2 and dc3. Which Consul feature allows a service in one datacenter to query services in another datacenter without additional configuration?
Medium13To verify if two datacenters are connected via WAN, which command shows the remote datacenter's server nodes?
Easy14A Consul operator wants to ensure that if the primary datacenter becomes unavailable, the secondary datacenter can continue to operate for existing services and intentions. Which statement best describes Consul's behavior in this scenario?
Easy15What is the benefit of using a Mesh Gateway in a multi-datacenter deployment with overlapping IP space?
Medium16You want to ensure that specific services in a remote datacenter are only accessible to certain local services. How can you achieve this?
Medium17A company runs a primary datacenter and a secondary datacenter with ACL replication enabled. During a maintenance window the primary's servers are taken offline for several hours while the secondary remains fully operational. What is the expected behavior in the secondary during the outage?
Hard18You are configuring a new Consul datacenter named 'dc2' to join an existing WAN federation with primary datacenter 'dc1' that uses mesh gateways. The WAN is not directly routable between datacenters. Which configuration allows dc2's servers to establish WAN federation through the mesh gateways?
Medium19What happens to the gossip protocol if the 'encrypt' key is mismatched between two datacenters trying to join via WAN?
Easy20When joining a new datacenter to an existing WAN pool, what is the best practice for server versions?
Easy21A new engineer is configuring a Consul server agent for a datacenter named 'west' and wants the agent to automatically rejoin the WAN federation after a restart without manual intervention. Which configuration setting should they use?
Easy22A platform team operates a Consul 1.15 cluster with a primary datacenter in us-east-1 and a secondary datacenter in eu-west-1. After configuring ACLs for replication, they update a token policy in the primary datacenter. A security engineer in the secondary datacenter immediately checks the ACL token and finds the old policy still in effect. What is the most likely reason the policy change has not propagated yet?
Medium23Which TWO of the following are valid ways to troubleshoot inter-datacenter communication issues?
Medium24What is the purpose of the 'datacenter' field in the Consul agent configuration?
Medium25You 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?
Easy26You are configuring a new Consul datacenter in a multi-datacenter federation. The datacenter must be able to join the existing WAN gossip pool and participate in cross-datacenter service discovery. Which two configuration settings are required on the new datacenter's Consul servers to enable WAN gossip and ensure secure communication? (Choose two.)
Hard27You are using Consul's DNS interface to query a service named 'web' in datacenter dc2 from a client in dc1. The query returns no results, but you know the service is running in dc2. What is the most likely reason?
Medium28You are managing a multi-datacenter Consul deployment with ACLs enabled. The primary datacenter is in dc1, and a secondary datacenter is in dc2. You have configured ACL replication in dc2 using acl_replication_token. After some time, you notice that new ACL tokens created in dc1 are not being replicated to dc2, and the replication status shows 'No known leader'. What is the most likely cause of this issue?
Hard29You have enabled ACL replication between a primary and secondary datacenter. What is the effect of changing an ACL policy in the primary datacenter?
Medium30A company runs Consul 1.15 in three datacenters: dc1 (primary), dc2, and dc3 (secondaries). The operations team wants to ensure that if dc1 becomes unavailable, the remaining datacenters can still authenticate services using existing ACL tokens. They have already configured ACL replication and WAN federation. Which statement best describes the expected behavior of ACL tokens in dc2 and dc3 during a primary datacenter outage?
Hard31A Consul 1.15 cluster spans three datacenters: dc1 (primary), dc2, and dc3. The operations team wants to enable cross-datacenter service discovery for a service named 'web' that is deployed in all datacenters. They configure a prepared query with a failover policy. Which statement accurately describes how the failover block in the prepared query affects query results when the local datacenter's 'web' service has no healthy instances?
Hard32A platform team operates two Consul datacenters, dc1 (primary) and dc2 (secondary), with ACLs enabled. They have configured token replication using a replication token in dc2. After rotating the replication token in dc1, they update the configuration in dc2 and restart the Consul agents. However, ACL replication stops working and dc2 logs show 'Permission denied'. What is the most likely cause?
Medium33Which file format is used for Consul configuration?
Medium34You have a Consul 1.15 cluster with two datacenters, dc1 and dc2, federated via WAN gossip. You want to use a prepared query to automatically failover to a service in dc2 if the service in dc1 becomes unhealthy. Which configuration in the prepared query is required to achieve this?
Medium35Which TWO of the following are true about Consul datacenters?
Medium36An operator has two Consul datacenters, 'dc1' and 'dc2', federated via WAN gossip. They want to query the health of a service named 'web' in dc2 from a Consul agent in dc1 using the HTTP API. Which endpoint should they use?
Easy37When using 'prepared_queries' for cross-datacenter failover, what does the 'failover' block allow you to specify?
Hard38You notice that the KV store is not consistent across datacenters. What is the cause?
Hard39A platform team operates two Consul datacenters, 'dc1' and 'dc2', and wants operators in dc2 to resolve service names registered in dc1 without a full mesh of local agents. They have already used 'consul join -wan' to link the server agents. Which feature should they rely on for DNS lookups of remote services?
Medium40When using multiple datacenters, what is the primary role of the 'consul-template' tool?
Medium41What is the recommended number of Consul servers per datacenter to ensure high availability?
Medium42Which protocol do Consul servers use to maintain the WAN gossip pool?
Easy43You are deploying a new Consul datacenter and need to configure the servers to join the existing WAN gossip pool. Which configuration parameter should you set on the new servers to specify the addresses of the existing WAN servers?
Easy44Which TWO of the following accurately describe Consul's WAN gossip protocol behavior?
Hard45An operator is troubleshooting a Consul datacenter that was recently federated with another datacenter. They notice that cross-datacenter service discovery works, but ACL tokens created in the primary datacenter are not being recognized in the secondary datacenter. What is the most likely cause?
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Frequently asked questions
- What does the Multi Datacenter Federation domain cover on the Consul 1.15 exam?
- Be able to configure and reason about federated datacenters: WAN gossip, primary/secondary replication, token rotation, and prepared query failover. The key point is that most Consul data, including KV, is datacenter-scoped and only specific data replicates.
- How many questions are in this domain?
- This page lists all 45 Multi Datacenter Federation questions in the Consul 1.15 question bank. The actual exam draws from this domain proportionally to its weighting in the official exam blueprint.
- What is the best way to practise this domain?
- Start with a short focused session (10 questions) to identify gaps, then work through explanations. Repeat with a longer session once the weak areas feel solid.
- Can I practise only Multi Datacenter Federation questions?
- Yes — the session launcher on this page filters questions to this domain only. Choose any session length for inline explanations and scoring.