Designing a robust Elastic cluster

Designing a robust Elastic cluster requires a deep understanding of Elasticsearch’s architecture, data distribution, and performance optimization techniques. This guide covers the key considerations for engineers to build and maintain a resilient and high-performing Elastic cluster.

Introduction

Designing a robust Elasticsearch cluster requires more than just spinning up a few nodes. Done right, it’s the foundation for scalable, fast, and fault-tolerant data systems. But the truth is—no cluster is “perfect” on the first try. The real goal is to design a cluster that evolves with your workload and scales without pain.

Let’s walk through a high-level yet actionable guide to building a future-ready Elastic deployment—whether you're dealing with firewalls, hybrid architecture, or 5+ TB/day ingestion.

Cluster Architecture and Node Roles

Proper role separation is your first step in building resilience.

From the field: Avoid single points of failure. As one Elastic pro shared, only one Logstash node per firewall zone can risk cluster downtime. Add redundancy or plan for fast failover setups.

Index Design and Sharding Strategy

Choosing the Right Shard Size

Your default might be 5 shards per index, but that’s often wrong.

  • <3M docs? → 1 shard
  • 3–5M docs? → 2 shards

5M docs? → (doc_count / 5M) + 1 (rounded up)

Avoid this trap: Over-sharding. It increases overhead and burdens master nodes.

Pro Tip: Aim for shard sizes between 10–50GB. If your shards are under 1GB or over 100GB, revisit your design.

Segment Management

Each Elasticsearch shard is a full Lucene index. The more segments you have, the slower your search becomes. Use ILM and force merges wisely:

Resource Allocation: CPU, Memory, and Storage

Heap Size & JVM Tuning

  • Allocate 50% of system RAM to heap, max 31–32GB.
  • Use mlockall to prevent swapping.
  • Prefer G1GC for heaps >4GB in modern Java 8+ environments.

Storage Choices

  • Use SSD over spinning disks.
  • Prefer RAID0 if you're running large clusters and can afford node loss.
  • Use JBOD if you need higher disk fault tolerance.

CPU Guidelines

  • CPU-bound clusters? Avoid relying solely on ingest nodes.
  • Tune thread pools carefully; monitor rejections.

Firewall and Security-Aware Cluster Design

In setups with internal firewalls, node placement is key. From a real-world Elastic thread:

  • Place Logstash forwarders outside and inside the firewall.
  • Fleet Server must be inside the firewall but reachable from agents.
  • Use firewall rules (not NAT) to expose:
    • 9200 (Elasticsearch)
    • 5601 (Kibana)
    • 8220 (Fleet agent → Fleet server)

Security Must-Haves:

  • Use TLS for all node-to-node and client traffic.
  • Set xpack.security.enabled: true
  • Enforce RBAC with service accounts or LDAP integrations

Fault Tolerance and Disaster Recovery

Best Practices:

  • 3 master nodes across 3 physical locations
  • Snapshot daily to S3 or Azure Blob using:

  • Use shard allocation awareness:

Advanced: Resilience in Multi-Zone and Large-Scale Deployments

Elastic’s Official Guidance:

If your nodes share infrastructure (same rack, power supply), consider them part of the same zone. A resilient cluster must tolerate full zone loss:

  • Place one copy of each shard in a different zone.
  • Use voting-only nodes to break ties in 2-zone deployments.
  • Spread Kibana, Fleet, and ingest nodes across multiple zones.

Elastic Tip: Never place master nodes equally between two zones. One must have a majority or you risk cluster paralysis during a network partition.

Network Recommendations

  • <10ms latency between nodes
  • 1Gbps minimum bandwidth (10Gbps recommended)
  • Use cross-cluster search or replication for remote data centers

Monitoring, Maintenance & Capacity Planning

  • Use Elastic’s Stack Monitoring to watch for disk skew, high JVM, and shard imbalance.
  • Automate index rollover with ILM based on age or size.
  • Set slow query logs:

Expect to redesign your cluster 2-3 times
-running elasticsearch-fun-profit

That’s not failure. It’s iteration.

Partnering with Hyperflex for Expert Support

Elasticsearch is elastic—but designing for elasticity requires real-world insight. That’s where we come in.

Why Hyperflex?

  • 24+ Elastic-certified engineers
  • Fast turnarounds with startup agility
  • 100% focused on Elastic consulting
  • Affordable migration & optimization offers (starting at $5K for 5 days)

Need help today?
Book a discovery call or download our free Elastic Optimization Checklist.

Final Takeaway

A robust Elasticsearch cluster is not born—it’s engineered. You’ll tune, break, scale, and evolve it over time. But by starting with smart architecture, sound resource allocation, and a firewall-aware security strategy, you’re already ahead.

Hyperflex helps teams scale Elastic fast-with confidence.
Contact us to explore how we can support your elastic journey