Atlas analytics nodes and read preference tags
Parent: Long-running secondary reads in sharded clusters · Published reference · snapshot 2026-10-31
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Source-anchored research for Atlas analytics nodes and read preference tags. Run status: COMPLETED.
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Definitions
- With secondaryPreferred, no eligible tagged secondary means fallback to the primary without applying tags. An analytics tag therefore does not prevent primary reads under this mode. (high confidence) [source]
How it works
- Inference from the Datadog and JDBC reports: verify destination-node metrics through the actual connector, because a syntactically plausible analytics-tag configuration does not prove that integration preserves or accepts it. (medium confidence) [source]
How-to and procedures
- Use readPreference=secondary&readPreferenceTags=nodeType:ANALYTICS to select analytics nodes for reads. Atlas and Fivetran document this exact combination. (medium confidence) [source]
Problems, failure modes and limitations
- Atlas warns that strict analytics targeting can fail during compaction initial sync, disk scale-down, and NVMe tier changes; its availability example adds an empty-tag fallback. (low confidence) (verified as of 2026-10-14) [source]
- A 2026 Terraform Google provider feature request describes missing MongoDB additional_options support for Datastream analytics-tag routing. It is evidence of a reported provisioning gap at that time, not a verified current provider limitation. (low confidence) [source]
- Datadog issue 17942 records a June 2024 Mongo integration configuration rejecting readPreferenceTags values with a not-a-valid-value error. A November 2024 contributor recommended per-host monitoring instances. This historical report does not establish a current driver-wide defect. (low confidence) [source]
Comparisons and alternatives
- With secondary and only the analytics tag set, lack of eligible matching secondaries causes read selection to fail rather than use the primary. (high confidence) [source]
- Atlas predefined replica-set tags differ from user-managed resource tags; users cannot change the predefined replica-set tags. (low confidence) [source]
Facts and statements
- Atlas provides fixed replica-set tags distinct from user-managed resource tags. nodeType:ANALYTICS identifies analytics nodes; workloadType:OPERATIONAL identifies electable and read-only nodes. (low confidence) (verified as of 2026-10-14) [source]
- Tag sets are tried in order; the first set matching eligible candidates wins. A trailing empty readPreferenceTags= under secondary permits fallback to other secondaries, broadening eligibility beyond analytics nodes. (high confidence) [source]
- In a sharded topology, the driver selects a mongos without applying read-preference tags to that choice. It forwards the read preference to mongos for downstream selection. (low confidence) [source]
- A September 2022 incident report describes analytics-node unavailability sending secondaryPreferred reads to the primary, degrading service and contributing to failover. The author changed the analytics connection to secondary. (low confidence) [source]
- DRIVERS-2563 records historical mongos replica-set-monitor bugs that did not honor tag-list preference order. It identifies SERVER-51835 and explains how queries could spread beyond the preferred hosts. This is historical evidence, not a claim that every current release is affected. (low confidence) [source]
- Datadog issue 17942 reports Mongo integration 6.2.0 rejecting configured analytics tags with "not a valid value for readpreferencetags". A Datadog contributor advised one monitoring integration instance per database host. (low confidence) [source]
- A July 2025 Atlas SQL JDBC issue reports analytics tags being ignored while secondary mode worked; the reporter observed correct analytics targeting through the native Java driver. Treat this as a connector-specific report, not proof that native Atlas routing ignores tags. (low confidence) [source]
- Atlas supplies nodeType:ANALYTICS for analytics secondaries. Its documented targeting string is readPreference=secondary&readPreferenceTags=nodeType:ANALYTICS&readConcernLevel=local. (high confidence) [source]
- Within one tag set, every specified key/value pair must match. Mode and maxStalenessSeconds filter candidates before ordered tag matching. (low confidence) [source]
Children
- No children recorded.