All components are installed in all servers but they are not necessarily activated, because special configuration is done.


In order to have high availability on the services, it’s important to maintain the rule N/2+1 rule, which means that more than half of the servers must be up, in order to provide service.


In this case, considering N = 3 ABIS node servers, you HA will work as long as more than the half of the servers is up, applying the formula, it’s required a minimum of 2 servers to keep operations up.


Let's assume this is the cluster configuration:

Server name

AMQ

Manager

Extractor

Dispatcher

Matcher

Node 1

ACTIVE

ACTIVE

ACTIVE

ACTIVE

ACTIVE

Node 2


BACKUP

BACKUP

BACKUP

ACTIVE

Node 3

BACKUP




ACTIVE



So the HA scenarios, keeping minimum 2 servers alive, (and all the template partitions at least in two servers) could be:

  1. Server 001 goes down

    Server name

    AMQ

    Manager

    Extractor

    Dispatcher

    Matcher

    Node 1

    GONE

    GONE

    GONE

    GONE

    GONE

    Node 2


    ACTIVE

    ACTIVE

    ACTIVE

    ACTIVE

    Node 3

    ACTIVE




    ACTIVE

  2. Server 002 goes down

    Server name

    AMQ

    Manager

    Extractor

    Dispatcher

    Matcher

    Node 1

    ACTIVE

    ACTIVE

    ACTIVE

    ACTIVE

    ACTIVE

    Node 2


    GONE

    GONE

    GONE

    GONE

    Node 3

    BACKUP




    ACTIVE

  3. Server 003 goes down

    Server name

    AMQ

    Manager

    Extractor

    Dispatcher

    Matcher

    Node 1

    ACTIVE

    ACTIVE

    ACTIVE

    ACTIVE

    ACTIVE

    Node 2


    BACKUP

    BACKUP

    BACKUP

    ACTIVE

    Node 3

    GONE




    GONE


As you can see, all the combinations following the N/2+1 rule, allows the system to continue operational, but if more than one server is down, then it would not be possible to maintain in memory not only the services but neither the three template partitions in memory; as the whole applicant database is to be split into three partitions, to have a mirror factor 2 (two entire copies of the applicant’s templates distributed in three partitions across the ABIS’ cluster nodes) as follows:


The ABIS database is partitioned, on this case, 3 partitions, as follows:


Fully operational ABIS Cluster (All partitions up, two full database mirrors)

Functional HA

Non-functional HA (missing database partitions)