Announcing a change to the default number of data members for Databases for MongoDB.
At IBM Cloud Data Services, we are tirelessly investigating improvements to our service in order to offer our customers the best possible price-to-performance ratio balanced with data availability and safety. As part of that work, we are changing the default number of data members for Databases for MongoDB from two to three. This change will occur sometime after October 4, 2020, and will be noticeable in our catalog page, under the feature description of our standard plan, and in our documentation.
Action required: Users who are passing in the following parameters to provision requests using the IBM Cloud CLI, Resource Controller API, or Terraform will need to update the values so they match the new three-member topology:
If they are passing these values, they will need to multiply the current value they're sending by 1.5. If they don't pass an allocation, no changes are necessary.
In addition to this architecture change, we recommend all users make use of majority write/read concerns to ensure data integrity. You can check out the MongoDB Java driver documentation for an example of how to employ majority write concern in your application tier.
All new Databases for MongoDB deployments in the week of October 4, 2020, will now be deployed in a Primary with Two Secondary Members (P-S-S). Previously, we deployed a Primary with a Secondary and an Arbiter (PSA). All Databases for MongoDB instances deployed before the change will remain on a PSA architecture; however, instances restored from backup (at the earliest of October 4) will be deployed with a P-S-S architecture, as well.
For further reading on MongoDB transaction semantics, we recommend Jepsen's independent, in-depth reviews of currently supported major versions:
This also means that any example deployment Databases for MongoDB with three members will be priced as follows:
If you have any questions or concerns, reach out through support referencing this announcement.