Terraform effective fields and auto-scaling drift
Parent: Atlas storage auto-scaling and disk reclaim via compact · Published reference · snapshot 2026-10-31
↓ Facts as markdownall context files
Source-anchored research for Terraform effective fields and auto-scaling drift. Run status: COMPLETED.
These notes link each claim to its source. Some citations identify archived research reports that are no longer hosted on this site. A published reference means the content is available; it does not certify independent review or accuracy.Read the editorial policy and follow the sources before relying on a claim.
How-to and procedures
- Enable use_effective_fields and remove spec ignore_changes together, without unrelated edits. Restore previously removed analytics/read-only blocks in a prior apply if validation requires it. (low confidence) (verified as of 2026-10-30) [source]
Problems, failure modes and limitations
- Historical first-person reports document the failure mode: a 2022 Terraform plan proposed disk shrinkage from 21 GB to configured 15 GB, and a 2023 Pulumi report describes reverting an auto-scaled M30 to configured M10. These reports establish historical reconciliation risk, not a current effective-fields defect. (medium confidence) [source]
Facts and statements
- For supported dedicated clusters, use_effective_fields separates configured sizing from effective provisioned sizing, preventing auto-scaling plan drift without spec ignore_changes blocks. (medium confidence) (verified as of 2026-10-31) [source]
- Effective fields support dedicated M10+ clusters, exclude Flex clusters, and do not apply to search nodes. (low confidence) (verified as of 2026-10-14) [source]
- For electable and read-only specs, either compute or storage auto-scaling preserves instance size, disk size and disk IOPS independently of configured values; the Atlas table lists only instance size for analytics specs. (low confidence) (verified as of 2026-10-14) [source]
- Read actual hardware through data-source effective_electable_specs, effective_read_only_specs and effective_analytics_specs; ordinary spec attributes describe configuration intent. (medium confidence) (verified as of 2026-10-30) [source]
- With effective fields and auto-scaling enabled, configured sizing changes do not affect live hardware. Disable compute and disk auto-scaling, apply desired specs, then re-enable scaling. (low confidence) (verified as of 2026-10-30) [source]
- Before disabling disk auto-scaling, nonzero advanced_configuration.oplog_min_retention_hours must be set to zero in a prior apply; otherwise HTTP 400 OPLOG_MIN_RETENTION_HOURS_NO_DISK_AUTO_SCALING can occur. (low confidence) (verified as of 2026-10-30) [source]
- For multiple replication_specs entries, the provider currently documents use_effective_fields as ineffective and advises against enabling it. (low confidence) (verified as of 2026-10-30) [source]
- Without effective fields, explicit ignore_changes protects auto-scaled sizing from reconciliation. Terraform uses ignored attributes at creation but ignores them for update planning. (medium confidence) [source]
- The changelog dates effective-fields resource support and effective-spec data-source outputs to provider 2.3.0, released December 9, 2025. (low confidence) [source]
- A 2023 provider issue records that static ignore_changes inside reusable modules blocks intentional instance-size updates in environments without auto-scaling. HashiCorp confirms ignored attributes are excluded from update planning. (medium confidence) [source]
Children
- Effective-spec data-source observability (frontier)
- Effective-fields migration safety (frontier)
- Multi-shard effective-fields limitations (frontier)
Frontier under this node: Effective-fields migration safety, Effective-spec data-source observability, Multi-shard effective-fields limitations