High Availability and Disaster Recovery

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High availability

• Redundant resource costs
• System performance
• System synchronization methods and the level of synchronization each method provides
• Computational costs
• Network latency

• Data Redundancy. Create multiple copies of the data on a single storage device to increase the probability of at least one copy being available at all times.
• Storage Redundancy. Distribute the data across multiple physical storage devices to ensure data is available if one of the physical storage devices is not accessible.
• Process/Pod Redundancy. Create multiple copies of each service/pod to reduce the risk of a service becoming unavailable if an individual copy fails for some reason.
• Process/Pod Distribution. Distribute duplicate pods across different nodes in a cluster to protect against the loss of service due to a failed node in the cluster.
• Node Redundancy. Create multiple nodes in the cluster within a single Availability Zone to protect against the loss of any single node. For this option:
  • The level of node over-provisioning is a function of both the probability of a node failing, and the average time required to provision and return a new node to service after a failure.
  • Sufficient redundancy means that if one node fails, the remaining nodes have sufficient computing capacity to manage the load while a new node is provisioned.
• Availability Zone Redundancy. Distribute resources across multiple zones to allow the system to tolerate the loss of an entire zone without compromising the availability of the system as a whole. While this is an option, Lucidworks does not use this because it does not consider this best practice.
• Cluster Redundancy. - Create multiple copies at the cluster level within a single data center to ensure that there is no loss of service even if an entire cluster is lost.
• Data Center Redundancy. Distribute clusters across multiple data centers in a region. If availability to a specific data center is lost, the system is still available in other data centers.
• Region Redundancy. Distribute clusters across multiple regions, for example, east and west. If a major outage occurs and availability to a specific region is lost, the system is still available in the other regions.

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Query runtime options

• Single cluster located in on-premise client hardware. This provides the lowest level of availability and disaster recovery if an outage or data corruption occurs.
• Single clusted deployed in the cloud. This provides the lowest cloud-based level of availability and disaster recovery if an outage or data corruption occurs.
• Active-Passive disaster recovery. Redundant clusters exist, but only one is running at a given time.
• Green-Blue-Active-Passive disaster recovery. Redundant clusters exist, but only one is available to service user requests.
• Active-Active disaster recovery. Redundant clusters exist that contain identical live infrastructure and all clusters are actively servicing user requests. For more information about the configurate to synchronize indexes between data clusters, see Active - Active.
• Green-Blue Active-Active disaster recovery. Redundant clusters exist that contain duplicate Kubernetes-deployed environments and all clusters are actively servicing user requests.
• Fully Active-Active Traffic Shaped disaster recovery. - Redundant clusters exist and all clusters are actively servicing user requests, with traffic directed to a specific cluster according to geography or user affinity.

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Fusion High Availability architecture types

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Fusion Disaster Recovery deployment architecture types

• data center configurations
• the actual data (indexes)

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Strategy to sync data center configuration

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Setups to sync indexes between data centers

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Active - Active

1. Hot - Hot: The data centers connect to a common node for good network bandwidth.
   1. Fusion clusters are on both data centers without Solr.
   2. Deploy Solr service on the common node.
   3. Both Fusion clusters connect to Solr node to GET/PUT catalog or signals records.
   4. Solr index has its own backup and restore procedure.
2. Hot - Warm: There is no common data node between the data centers.
   1. Deploy Fusion full stack clusters on both data centers.
   2. Use Fusion connectors or PBL job to transfer catalog and signals from one datacenter to another.
   3. Solr index is already replicated on both data centers.
   4. During data transfer, it is possible that data is not fully synchronized.

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Active - Passive

1. Hot - Cold
   1. Fusion has 1-2 nodes on the secondary datacenter.
   2. Configurations are periodically copied over to the secondary data center.
   3. Connectors job is set up to copy indexes.
   4. Could also take periodic Solr Active cluster backups and cache them temporarily so the most recent backup is always available to restore into the Cold cluster when it starts.

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Data transfer options

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Fusion Parallel Bulk Loader (PBL) job

• Pros include:
  • Easy to configure Fusion Spark job.
  • Blazing fast batch transfer with scheduling and monitoring options available.
  • Configurable to filter out documents.
• Cons include:
  • None, because this option does not need to run Spark services.

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Solr streaming expressions

daemon(id="uniqueId",
    runInterval="5000",
    terminate="false",
    commit(Target,
 batchSize=5000,
 update(Target,
     batchSize=500,
     topic(
  Source-Checkpoint-Coll,
  Source,
                zkHost="localhost:9983/solr",
                q="*:*",
                fq="mimeType_s:application/pdf",
    fl="id,*",
                sort="id asc",
                qt="/export"
      )
         )
     )
)

• Pros include:
  • Keeps track of what has been read to date and only sends what is new.
  • Open source and easy to configure.
  • Does not depend on shard or replica count, and will tolerate differences on either end of the transaction.
  • Tolerates source-side outages and picks up where it left off.
• Cons include:
  • Can only send stored fields.
  • Not parallelizable like Spark jobs.
  • Does not tolerate destination-side outages. When the target is not available, data transfers can drop because the source-side high-water-mark may move before the target-side failure is detected.