88 lines
3.4 KiB
Org Mode
Executable File
88 lines
3.4 KiB
Org Mode
Executable File
#+TITLE: High Availability, Disaster Recovery and Business Continuity
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#+OPTIONS: num:nil
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#+DATE: <2026-03-11 Wed 17:18>
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#+filetags: :learning:notes:
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#+WIP:
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#+COMMENTS: t
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#+SLUG: high-availability-disaster-recovery
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* HA, DR and BC Competency Log
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Understanding High Availability (HA), Disaster Recovery (DR), and
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Business Continuity Planning (BCP) is important when designing reliable
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systems and analysing service incidents. These concepts help Microlise
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(and organisations in general) to minimise downtime, recover from
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failures, and maintain service availability.
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*** High Availability (HA)
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High Availability focuses on preventing service disruption by using
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redundancy. Systems are designed with backup components so that if one
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fails, another can take over automatically.
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Examples include:
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- Redundant servers or network paths
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- Load balancing across multiple systems
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- Automatic failover modes
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This ensures services continue operating even when individual components
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fail. We have this at Microlise where if there is a failure on one of
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the data centres, we can failover to the other one.
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An analogy from the article compares this to a bicycle with two brakes.
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The bike can operate with only one brake, but having two provides
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redundancy in case one fails.
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*** Disaster Recovery (DR)
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Disaster Recovery focuses on restoring systems after a major failure.
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This includes recovering infrastructure, applications, and data so
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services can resume operation.
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Some of the common DR tools and methods include:
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- Offsite backups
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- Replicated environments (e.g., multiple data centres with sync)
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- Recovery procedures and restoration tools
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Unlike High Availability, which tries to prevent downtime, DR assumes a
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failure has already occurred. In the bicycle analogy, after the crash
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the rider takes a bus home and then drives to work to complete their
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important task. This represents a recovery process after a major
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disruption.
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*** Business Continuity Planning (BCP)
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BCP ensures the business can continue operating during or after a
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disruption. This may involve alternative systems, temporary processes,
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or backup locations to keep services running.
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In the analogy, the car at home represents BCP because it allows the
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rider to continue their journey despite the broken bicycle. A Business
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Impact Assessment (BIA) helps determine the priority of services and the
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acceptable level of downtime.
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*** RTO and RPO
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Two key recovery metrics are:
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- Recovery Time Objective (RTO): The maximum time allowed to restore a
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service after failure. For example, if a critical service must be
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restored within 4 hours, the disaster recovery process must ensure
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systems are operational within that timeframe.
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- Recovery Point Objective (RPO): The maximum acceptable amount of data
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loss.
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RPO example:
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- An RPO of 0 minutes means no data loss is acceptable.
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- An RPO of 1 hour means up to one hour of data could be lost.
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These values help define the required level of HA and DR design.
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*** Application in Real Scenarios
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These concepts are useful when performing incident debugging, root cause
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analysis, or explaining service issues to customer support teams. For
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example, engineers may check whether failover worked correctly, whether
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recovery met the RTO, or whether backups allowed data to be restored
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within the RPO.
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In summary, the reason why we need to understand HA, DR, and BCP is to
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maintain service availability and ensure business continuity.
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