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#availability

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Tagged #availability

GuideTechnology

14 min read

High Availability and Disaster Recovery: Redundancy, Failover, RPO, RTO and Multi-Region

How systems survive failures of servers, availability zones and whole regions, and recover from data disasters. Covers failure domains, redundancy and failover, availability arithmetic with correlated failures, RPO and RTO, the four disaster-recovery strategies from backup-and-restore to active-active, multi-region write strategies, backups that actually restore, and safe deployments.

GuideTechnology

15 min read

Database Replication: Primary-Replica, Read Replicas, Lag and Failover

Why databases keep copies on several machines, and what those copies cost. Covers primary-replica replication, synchronous versus asynchronous replication, read replicas for scaling, replication lag and the read anomalies it causes, read-your-writes routing, failover and split brain, multi-leader and leaderless replication, and why replication is not a backup.

GuideTechnology

18 min read

Load Balancers: How They Work, Algorithms, Health Checks and Stateless Services

Why load balancers exist, how they spread traffic across servers, and what makes that possible: stateless services. Covers Layer 4 versus Layer 7, reverse proxies, round robin, weighted, least connections and hashing, health checks, draining, sticky sessions, redundancy of the load balancer itself, and autoscaling.