Tier has two different definitions, depending on whether you’re talking about server architecture or Acquia subscriptions.
Server architecture
In server architecture, tier refers to whether you have multiple types of servers.
The following list describes the different tiers as it pertains to the Acquia Platform:
Multi-tier: Multi-tier subscribers have Apache and MySQL running on separate servers.
For example, a multi-tier subscriber’s production environment can have a set of web servers (web-123 and web-124) running Apache, and a set of database servers (
fsdb-123andfsdb-124) running MySQL.Single-tier: Single-tier subscribers have Apache and MySQL running on the same server(s).
Note for Cloud Platform users
Cloud Platform Enterprise-level subscribers can be either single-tier or multi-tier; all Cloud Platform Professional subscribers are single-tier.
Acquia subscriptions
Acquia subscribers have subscriptions that define their tier, which in turn defines the level of support they’re entitled to receive. For more information about subscription tiers, see: