Scenario: Loss of a non-primary database: Modular Cluster#

  • The administrator deployed the cluster into a Primary and DR site.

  • The cluster is deployed following the Installation Guide.

  • The example is a typical cluster deployment: 8 nodes, where 3 nodes are database servers, 3 nodes are application nodes and 2 nodes are proxy servers.

    The design is preferably split over 2 physical data centers.

Database Node Failure#

  • Normal operations continue where the cluster is processing requests and transactions are committed successfully up to the point where a loss of a non-primary node is experienced.

    In this example, DB02[172.29.42.104] failed while transactions were running.

  • Examine the cluster status running cluster status to determine the failed state:

Data Centre: unknown

            database : unknown_172.29.42.104[172.29.42.104] (not responding)


Data Centre: jhb
              application : AS01[172.29.42.100]
                            AS02[172.29.42.101]

              webproxy :    PS01[172.29.42.102]

              database :    DB01[172.29.42.103]

Data Centre: cpt
              application : AS03[172.29.21.100]

              webproxy :   PS02[172.29.21.102]

              database :   DB03[172.29.21.101]

  • At this point, all transactions that are currently in flight are lost and will not recover.

  • The lost transactions have to be replayed or rerun.

    Bulk load transactions cannot be replayed and have to be rerun. Before resubmitting a failed Bulk load job, carry out the following command on an application node in order to manually clear each failure transaction that still has a Processing status after a service restart. Use the command:

    voss finalize_transaction <Trans ID>

    The failed transaction status then changes from Processing to Fail.

  • With the database server DB02[172.29.42.104] still down, replaying the failed transactions are successful.

Recovery steps#

If the server that is lost, is unrecoverable:

  1. A new database node needs to be deployed. Ensure the server name, IP information and data center name is the same as on the server that was lost.

  2. Delete the failed node database weight (database weight del <ip>), for example database weight del 172.29.42.104

  3. Run cluster del 172.29.42.104, because this server no longer exists. Power off the deleted node, or disable its Network Interface Card.

  4. Run cluster provision on the cluster without the node to be added.

    Then create the new database node at the required data center - see: Create a New VM Using the Platform-Install OVA and switch on the newly installed node.

  5. From the primary database node, run cluster add <ip>, with the IP address of the new database node to add it to the existing cluster.

  6. Add database weights so that the weights distributed throughout the cluster

    • Delete all database weights in the cluster. On the primary database node, for each database node IP, run database weight del <IP>.

    • Re-add all database weights in the cluster. On each database node, for each database node IP, run database weight add <IP> <weight>

    • Check weights - either individually for each node, or for the cluster by using the command:

      cluster run application database weight list

      Make sure all database nodes show correct weights.

  7. Run cluster provision to join the new database node to the cluster communications. It is recommended that this step is run in a terminal opened with the screen command.

  8. If an OVA file was not available for your current release and you used the most recent release OVA for which there is an upgrade path to your release to create the new database node, re-apply the Delta Bundle upgrade to the cluster.

    Note that the new node version mismatch in the cluster can be ignored, since this upgrade step aligns the versions.

    See: Upgrade

Note

Upon cluster provision failure at any of the proxy nodes during provisioning, the following steps illustrate the cluster provisioning:

  1. Run database config and check if nodes are either in STARTUP2 or SECONDARY or PRIMARY states with correct arbiter placement.

  2. Login to web proxy on both primary and secondary site and add a web weight using web weight add <ip>:443 1 for all those nodes that you want to provide a web weight of 1 on the respective proxies.

  3. Run cluster provision to mitigate the failure. It is recommended that this step is run in a terminal opened with the screen command.

  4. Run cluster run all app status to check if all the services are up and running after cluster provisioning completes.

Note

If the existing nodes in the cluster do not see the new incoming cluster after cluster add, try the following steps:

  1. Run cluster del <ip> from the primary database node, <ip> being the IP of the new incoming node.

  2. Run database weight del <ip> from the primary database node, <ip> being the IP of the new incoming node.

  3. Log into any non primary database node and run cluster add <ip>, <ip> being the IP of the new incoming node.

  4. Run database weight add <ip> <weight> from the same session, <ip> being the IP of the new incoming node.

  5. Use cluster run database cluster list to check if all nodes see the new incoming nodes inside the cluster.