Skip to main content

High Availability

Fault tolerance​

Fault tolerance is the ability of the system to stay up despite taking hits.

Failure reasons​

  • Software crashes

  • Hardware Failures

  • Human errors This is an interesting read.

  • Planned Downtown: maintenance operations, software, hardware upgrade.

Fail soft:A few of the instances/nodes, out of several, running the service go offline & bounce back all the time. In case of these internal failures, the system could work at a reduced level but it will not go down entirely.

Highly Available Fault-Tolerant Service.

the entire massive service is architecturally broken down into smaller loosely coupled services called the micro-services

micro-service-scale.jpeg

Redundancy​

Active-Passive HA Mode​

high-availability.jpeg

GPS, aircrafts, communication satellites which have zero downtime. The availability of these systems is ensured by making the components redundant.

Single point failure: Distributed systems​

Monitoring & Automation - to cut down human errors​

Replication​

Active-Active High Availability​

HA-replication.jpeg

Geographical Distribution of Workload​

High Availability Clustering​

A High Availability cluster also known as the Fail-Over cluster contains a set of nodes running in conjunction with each other that ensures high availability of the service. Heartbeat network monitors the health.

A single state across all the nodes in a cluster is achieved with the help of a shared distributed memory & a distributed co-ordination service like the Zookeeper.

HA-cluster.jpeg

e.g. Jenkins master and clients.

Disk mirroring/RAID Redundant Array Of Independent Disks, redundant network connections, redundant electrical power

Which of the following statements is true in context to scalability & high availability?

Scaling an application horizontally means getting rid of single points of failure & that means the application also becomes highly available.