High Availability
High availability (HA) architecture
Deployments with single points of failure removed and a defined failover scenario. When a component fails, the service continues by design rather than by hope.
- Duplication of critical components
- Redundant
- Defined takeover scenario
- Failover
- Scenario tested regularly
- Rehearsal
- Cluster traffic on the private network
- Isolated network
Finding the single point of failure
Designing for high availability starts with a single question: what happens if this component fails right now? You have to ask it separately for every box in the architecture — web server, database, cache, load balancer, even the routing configuration.
Every point where the answer is "the service stops" is a single point of failure. Listing them matters more than the fix, because in most organisations which component lacks redundancy is only discovered when it fails.
Redundancy is not built the same way everywhere. Web servers may need only a second instance and a load balancer, while the database needs replication and a takeover scenario; caching needs replication, and routing needs a second defined path.
The most critical and most often neglected part is testing the takeover. You only know failover works once you have actually tried it. We rehearse the scenarios at regular intervals, measure takeover duration and feed the result back into the plan.
- Single-point-of-failure analysis run for each component
- Redundancy method differs by component
- The takeover scenario is documented
- Failover is rehearsed on a schedule
- Cluster communication runs on the isolated private network
Comparison
Redundancy methods by component
| Component | Redundancy method | Takeover |
|---|---|---|
| Web / application server | Multiple instances | Load balancer redirects |
| Database | Replication | Replica assumes primary role |
| Cache (Redis) | Replicated deployment | Replica takes over |
| Storage | Hardware RAID | Continues without interruption |
| Network | Redundant path | Alternative route |
Questions an HA design must answer
- Which components run without redundancy?
- Will takeover be automatic or manually triggered?
- How long does takeover take, and does that meet target?
- How will the application learn the new address?
- How will data consistency be verified after takeover?
- What are the steps for failback to normal?
- When was the scenario last rehearsed?
- What happens in the event of a false alarm?
FAQ
Frequently asked questions
How much uptime does high availability deliver?
No architecture reduces downtime to zero; the goal is keeping outage duration under the limit you accept. That is determined by which components are made redundant and how long takeover takes. Once we discuss your target, we design the matching architecture together.
How much does HA increase cost?
Every redundant component means extra resources, so cost rises. But not every component needs redundancy: a criticality analysis limits duplication to the components whose failure genuinely affects the business, which is how you find the balance between cost and risk.
Should failover be automatic?
It depends. Automatic takeover shortens downtime but carries false-alarm risk: a transient network issue triggering failover can leave two servers both claiming the primary role. We choose automatic or controlled takeover based on criticality and scenario complexity.
More
Related pages
- PostgreSQLPostgreSQL cluster deploymentRead replicas with streaming replication, a failover scenario and point-in-time recovery. NVMe storage and replication over an isolated private network.
- Disaster RecoveryDisaster recovery planningA disaster recovery plan built on RTO and RPO targets: recovery ordering, a secondary copy at a separate site and regular rehearsals.
- Network10 Gbps isolated VLAN networkingAn isolated VLAN per customer, 10 Gbps private server-to-server networking and rule-based segment transit. Private traffic does not consume internet quota.
- RedisRedis and high-availability replicationReplicated Redis deployments for caching, session storage, queues and rate limiting. Persistence, eviction policy and memory monitoring configured.
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