Using failover in a Neptune global database - Amazon Neptune
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Using failover in a Neptune global database

A Neptune global database provides more comprehensive failover capabilities than a standalone Neptune DB cluster does. Using a global database, you can plan for and recover from disaster fairly quickly. Disaster recovery is generally assessed using evaluation of the recovery-time objective (RTO) and the recovery-point objective (RPO):

  • Recovery-time objective (RTO)   —   This is how fast a system returns to a working state after a disaster. In other words, RTO measures downtime. For a Neptune global database, RTO can be in the order of minutes.

  • Recovery-point objective (RPO)   —   The amount of time during which data is being lost. For a Neptune global database, RPO is typically measured in seconds (see Performing managed planned failovers for Neptune global databases).

For a Neptune global database, there are two different approaches to failover:

  • Detach-and-promote (manual unplanned recovery)   —   To recover from an unplanned outage or to do disaster-recovery testing (DR testing), perform a cross-region detach-and-promote on one of the secondary DB clusters in the global database. The RTO for this manual process depends on how quickly you can perform the tasks listed in Detach and promote. The RPO is typically a number of seconds, but this depends on the storage replication lag across the network at the time of the failure.

  • Managed planned failover   —   This approach is intended for operational maintenance and other planned operational procedures such as relocating the primary DB cluster of the global database to one of the secondary regions. Because this process synchronizes secondary DB clusters with the primary before making any other changes, RPO is effectively 0 (that is, there is no data loss). See Performing managed planned failovers for Neptune global databases.

Detach-and-promote a Neptune global database in the case of an unplanned outage

In the very rare situation where your Neptune global database experiences an unexpected outage in its primary Amazon Web Services Region, your primary Neptune DB cluster and its writer node become unavailable, and the replication between the primary cluster and the secondaries ceases. To minimize both the resulting downtime (RTO) and data loss (RPO), quickly perform a cross-region detach-and-promote to reconstruct the global database.

Tip

It's a good idea to understand this process before using it, and have a plan in place to proceed quickly at the first sign of a region-wide issue.

  • Use Amazon CloudWatch regularly to track lag times for the secondary clusters so that you can identify the secondary region with the smallest lag time if you need to fail over.

  • Make sure to test your plan to check that your procedures are complete and accurate.

  • Use a simulated environment to make sure your staff is trained and ready to perform a DR failover rapidly if it ever becomes necessary.

To fail over to a secondary cluster after an unplanned outage in the primary region

  1. Stop issuing mutation queries and other write operations on the primary DB cluster.

  2. Identify a DB cluster in a secondary Amazon Web Services Region to use as the new primary DB cluster of the global database. If the global database has two or more secondary Amazon Web Services Regions, choose the secondary cluster that has the smallest lag time.

  3. Detach that secondary DB cluster that you chose from the Neptune global database.

    Removing a secondary DB cluster from a Neptune global database immediately stops the replication of data from the primary to that secondary and promotes it to a standalone DB cluster with full read/write capabilities. Any other secondary clusters in the global database will still be available and can accept read calls from your application.

    Before recreating the Neptune global database, you will also have to detach the other secondary clusters to avoid data inconsistencies among the clusters (see Removing a cluster).

  4. Reconfigure your application to send all write operations to the standalone Neptune DB cluster that you chose to become the new primary cluster, using its new endpoint. If you accepted the default names when you created the Neptune global database, you can change the endpoint by removing the -ro from the cluster's endpoint string in your application.

    For example, the secondary cluster's endpoint my-global.cluster-ro-aaaaaabbbbbb.us-west-1.neptune.amazonaws.com becomes my-global.cluster-aaaaaabbbbbb.us-west-1.neptune.amazonaws.com when that cluster is detached from the global database.

    This Neptune DB cluster becomes the primary cluster of a new Neptune global database when you start adding regions to it in the next step.

  5. Add an Amazon Web Services Region to the DB cluster. When you do this, the replication process from primary to secondary begins. See Adding secondary global database regions to a primary region in Amazon Neptune .

  6. Add more Amazon Web Services Regions as needed to recreate the topology needed to support your application.

Make sure that application writes are sent to the correct Neptune DB cluster before, during, and after making these changes. Doing this avoids data inconsistencies among the DB clusters in the Neptune global database (these are known as split-brain issues).

Performing managed planned failovers for Neptune global databases

Managed planned failover let you relocate the primary cluster of your Neptune global database to a different Amazon Web Services Region whenever you choose. Some organizations will want to rotate their primary cluster locations on a regular basis.

Note

The managed planned failover process described here is intended to be used on a healthy Neptune global database. To recover from an unplanned outage or to do disaster recovery (DR) testing, follow the detach and promote process instead.

During a managed planned failover, your primary cluster is failed over to your choice of secondary region while your global database's existing replication topology is preserved. Before the managed planned failover process begins, the global database synchronizes all secondary clusters with its primary cluster. After ensuring that all clusters are synchronized, the managed planned failover begins. The DB cluster in the primary region becomes read-only, and the chosen secondary cluster promotes one of its read-only instances to full writer status, thus allowing the cluster to assume the role of primary cluster. Because all secondary clusters were synchronized with the primary at the start of the process, the new primary continues operations for the global database without losing any data. The database is only unavailable for a short time while the primary and selected secondary clusters are assuming their new roles.

To optimize application availability, perform the failover during nonpeak hours, at a time when writes to the primary DB cluster are minimal. Also, take the following steps before starting the failover:

  • Take applications offline wherever possible to reduce writes to the primary cluster.

  • Check lag times for all secondary Neptune DB clusters in the global database and choose the secondary with the least overall lag time to become the primary. Use Amazon CloudWatch to view the NeptuneGlobalDBProgressLag metric for all secondaries. This metric tells you how far a secondary is behind the primary DB cluster, in milliseconds. Its value is directly proportional to the time Neptune will take to complete the failover. In other words, the larger the lag value, the longer the failover outage will be, so choose the secondary with the least lag. See Neptune CloudWatch Metrics for more information.

During a managed planned failover, the chosen secondary DB cluster is promoted to its new role as primary but it doesn't inherit the complete configuration of the primary DB cluster. A mismatch in configuration can lead to performance issues, workload incompatibilities, and other anomalous behavior. To avoid such issues, resolve the following kinds of configuration differences between global database clusters before failover:

  • Configure parameters in the new primary to match the current primary.

  • Configure monitoring tools, options, and alarms   —   Configure the DB cluster that will be the new primary with the same logging ability, alarms, and so on that the current primary has.

  • Configure integrations with other Amazon services   —   If your Neptune global database integrates with Amazon services, such as Amazon Identity and Access Management (IAM), Amazon S3, or Amazon Lambda, make sure these are configured as needed to integrate with the new primary DB cluster.

When the failover process completes and the promoted DB cluster is ready to handle write operations for the global database, make sure to change your application(s) to use the the new endpoint for the new primary.

Using the Amazon CLI to initiate managed planned failover

Use the failover-global-cluster CLI command (which wraps the FailoverGlobalCluster API) to fail over your Neptune global database:

aws neptune failover-global-cluster \ --region (the region where the primary cluster is located) \ --global-cluster-identifier (global database ID) \ --target-db-cluster-identifier (the ARN of the secondary DB cluster to promote)
Note

The failover-global-cluster API is not available in the preview. It will be a part of the GA release.