EX294 Coordinate rolling updates Practice Question
A team uses Ansible to update a database cluster with one primary and two replicas. The goal is zero downtime. Which update order is the safest?
⚠ Common exam trap
Test-takers frequently assume updating the primary first is safer because it is the 'source of truth,' but in a clustered environment with zero-downtime requirements, updating replicas first is the standard practice to preserve write availability and allow safe rollback.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Update replicas first, then the primary.
Updating replicas first ensures that if the update introduces a regression, it affects only the read-only replicas, which can be quickly rolled back without impacting write availability. Once replicas are confirmed healthy, the primary is updated and a controlled failover (e.g., using `patronictl switchover` or `repmgr standby switchover`) promotes a replica to primary, minimizing downtime to seconds. This order aligns with the principle of reducing blast radius and maintaining quorum in a cluster.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Update replicas first, then the primary.
Why this is correct
Updating replicas first keeps the primary serving traffic throughout, so no write outage occurs. Each replica is drained from the load balancer, patched, and rejoined before touching the next. Only after both replicas run the new version is the primary failed over and updated, satisfying the zero-downtime constraint.
- ✗
Update in random order.
Why it's wrong here
Random ordering gives no control over which node is updated when, so a replica could be patched while the primary still runs incompatible code, breaking replication. Random selection suits stateless fleets where any host can be replaced independently.
- ✗
Update all nodes simultaneously.
Why it's wrong here
Updating every node at once takes the entire cluster offline, since no primary or replica remains to serve queries. Simultaneous updates are acceptable for stateless web tiers behind a load balancer, where other instances absorb the traffic.
- ✗
Update the primary first, then replicas.
Why it's wrong here
Updating the primary first causes a failover or write outage, so replicas briefly serve stale or unavailable data. Replicas should be updated before the primary, allowing promotion and rollback. Primary-first is tempting because it mirrors the cluster's logical hierarchy, but it inverts the safe rolling order.
Quick reference
AAA Protocol Comparison
| Protocol | Port(s) | Encryption | Transport | Primary Use |
|---|---|---|---|---|
| RADIUS | 1812 / 1813 | Password only | UDP | Network access control |
| TACACS+ | 49 | Full packet | TCP | Device administration |
| Diameter | 3868 | Full session | TCP / SCTP | Carrier / mobile networks |
| 802.1X | — | EAP-based | Layer 2 | Port-based access control |
TACACS+ encrypts the entire packet; RADIUS only encrypts the password field — a key exam distinction.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This EX294 practice question is part of Courseiva's free Red Hat certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the EX294 exam.