This article describes the infrastructure used for Black Pear's eSP app.
Infrastructure
Hosting
Black Pear apps are hosted as a Microsoft Azure Web App
Black Pear services are hosted on Amazon Web Services (AWS) using a Virtual Private Cloud (VPC) in the EU (London) region [eu-west-2].
Network
Connection to NHS networks is provided by Redcentric, an NHS Digital approved N3 aggregator, using an approved Logical Connection Architecture. Redcentric use AWS Direct Connect to provide a physical connection between NHS networks and the VPC.
Third parties
Some services used for additional eSP modules are dependent on APIs provided by Black Pear partners: NHS Digital, EMIS Health, TPP, Vision Health and Docman.
Resilience
Web Apps are available from multiple data centres across Europe to ensure continuity of service in the event of failure in one data centre.
Services are hosted in multiple AWS availability zones in the EU (London) region. For each service, a minimum of N+1 instances are deployed in conjunction with a load balancer in active-active configuration to ensure continuity of service in the event of failure of an instance. Instances are deployed across multiple availability zones (think of an availability zone as a data centre) to ensure continuity of service in the event of a failure in one availability zone. It is not possible to provide continuity in the event of failure of the entire region as this would require the services to process data outside the UK.
Automated health checks are used to detect and replace failed instances; autoscaling is used to detect services reaching capacity limits and to add extra instances to provide additional capacity.
Two network connections are deployed at different physical locations. These operate in an active-passive configuration to ensure continuity of service in the event of failure at one location.
Recovery
All hosted services are routinely deployed using CloudFormation templates to provide fast and repeatable deployments.
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