SQL Server AlwaysOn is the high-availability architecture that sits behind the failover-rights entitlement on SA-bearing licences. The Admodum read on the synchronous and asynchronous replica patterns, the licence-charge boundary, and the audit posture.
AlwaysOn Availability Groups (the full architecture on SQL Server Enterprise Edition) supports up to eight secondary replicas in current versions, with synchronous-commit, asynchronous-commit and read-only routing modes per replica. Basic Availability Groups (the cut-down, Standard Edition pattern) supports one primary and one secondary, no read-only routing, no backup offload.
The architecture is independent of the underlying high-availability layer (Windows Server Failover Clustering on Windows, Pacemaker on Linux). The licence implications run at the SQL-replica level, not the cluster-layer level. The wider SQL Server licensing framework reads against this spoke; the wider Software Assurance benefits overlay is the entitlement carrier.
The Software Assurance failover-rights entitlement permits a single passive synchronous secondary replica at no incremental SQL licence cost, provided the replica is a true passive instance (no active queries, no reporting load, no backup beyond the standard failover-replication maintenance).
The current product terms extend the entitlement to a primary plus a synchronous secondary plus an asynchronous DR replica in a separate datacentre or cloud region, under specific terms (the DR replica must be on a separate fault domain; the buyer-side declaration is the deployment topology). The Azure Hybrid Benefit applies to the DR replica when the secondary runs on Azure under SA.
Read-only routing is the AlwaysOn feature that directs intentionally read-only sessions to a secondary replica. The feature is structurally attractive (offload reporting from the primary; scale reads horizontally) and structurally expensive: a replica that serves read-only traffic loses the passive-replica status on the failover-rights entitlement and triggers a full per-core licence requirement on that replica.
The Admodum read on the workload-design decision is the gross-cost calculus: a four-replica Availability Group with three of the four replicas serving read-only routing carries four full per-core licence sets, not one. The wider SAM audit anatomy reads the read-only-routing configuration on inspection.
Backup offload (running the production backup job against the secondary replica to reduce primary-replica load) is permitted on the passive-replica status under current terms, provided the backup is the standard maintenance pattern (the backup of the replica state, not a separate reporting backup or a separate data-extraction job). The boundary is narrower than many buyers assume.
The permitted pattern is the standard SQL Agent backup job against the secondary replica. The not-permitted patterns include data-extraction jobs against the secondary (ETL into a downstream system; export to a reporting database), reporting-platform queries against the secondary (Power BI scheduled refresh; SSRS subscription) and any read query that is not a backup operation. The wider Power BI data-source reading is the principal cross-link audit catches.
The 90-day license-mobility rule applies between the synchronous-secondary roles when the secondary is reassigned across hosts (a hardware refresh, a cluster reconfiguration, a planned migration). The buyer-side rule is one license-mobility transition per 90 days per licence; the audit-side rule is the move-history declaration.
The frequent misuse pattern is the cluster-rebuild that moves all replica licences across hosts more than once per 90-day window: the audit reads the move history; the second-move-within-90-days transition becomes a license-non-compliance finding. The wider True-Up mechanics framework is the renewal-window true-up vehicle.
The buyer-side artefacts to hold against the AlwaysOn estate are: the Availability Group topology (every group, every replica, every commit mode, every replica role), the read-only routing configuration (every replica, every routing list, every connection-string read), the backup-job inventory (every job, every replica target, every job type), the license-mobility history (every move, every host, every date), the Hybrid Benefit register (every Azure-side DR replica, every SA licence applied).
The wider engagement sits in the Microsoft practice; the aggregated reading list sits in the Microsoft knowledge hub; active renewal moments route to the Renewal Programme; active audit moments route to Audit Defence.
The per-core model and the editions against which AlwaysOn carries the failover entitlement.
The maintenance overlay that carries failover rights and license mobility.
A senior Admodum Microsoft advisor will read your Availability Group topology, your read-only routing configuration and your backup-job inventory against the failover-rights entitlement on a private call. Active audit moments route to Audit Defence.