Acquia Cloud Enterprise is designed for high availability, with guaranteed 99.95% uptime. This page describes how Acquia delivers Acquia Cloud Enterprise's high availability.
High availability architecture
Acquia Cloud is built on Amazon Web Services (AWS) infrastructure, which is physically remote from the Acquia offices. Acquia Cloud customers may choose the geographic region for their application's location.
Each region contains multiple Availability Zones. AWS Availability Zones are separate yet interconnected data centers within the major regions. Acquia Cloud Enterprise offers high availability by using multiple AWS Availability Zones in one AWS region with redundant servers serving each layer of the technology stack. The following are the three main components of a Drupal application hosted by Acquia Cloud Enterprise:
- Reverse proxy caching and load balancing servers (Nginx and Varnish)
- Web servers (Apache with PHP and Drupal code)
- Database servers (Percona (MySQL))
At the Internet-facing tier, a software-based load balancer is deployed with a hot standby in a different availability zone in the same region. The load balancer distributes load across multiple web servers, which are also distributed across multiple availability zones. Acquia's expert operations team adds additional web servers to the resource pool as needed. The load balancer continuously monitors the web servers, and if a server becomes unavailable, it removes it from the pool of hosts serving the application. Web servers use a shared network file system (GlusterFS) so that all files are kept in sync and redundant to each other.
At the database layer, a scalable database cluster serves the application with active and passive database servers in multiple availability zones. The active master database server continuously updates the passive master database using MySQL replication. In the event of a failure of the master database, the passive database becomes primary through a DNS-based failover.
It is Acquia’s policy to restore customer services in the event of a major disaster in the best time frames. If the services in the current zone or region were severely impacted, Acquia would do its best to restore services in an alternate Availability Zone or region.
Disaster Recovery - Multiregion replication
Optionally, for customers with very high availability requirements, Acquia offers Acquia Cloud Enterprise customer environments with hot standby applications in an alternate region, thus providing live failover capabilities for disaster recovery.