The logical design must also include information about the dependencies for infrastructure and application services, in order to better understand the possible implications of a service or a component failure.
Service dependencies can be described with an entity relationship diagram with upstream and downstream dependencies:
- An upstream dependency is an entity that depends on another service
- A downstream dependency is an entity that another service depends on
- Each dependency connection must use an arrow that points to what the service depends on
These types of graphs can really help to better understand how service availability can affect other services, and it’s crucial for the risk management and design processes to minimize the dependencies at the infrastructure level. For example, the usage of two different vCenter servers, both in the management cluster, is a consequence of this approach.
One interesting VMware tool that can help in the activity of mapping services and dependencies is VMware vRealize Infrastructure Navigator (it works only on existing vSphere environments and only for VMs with running VMware Tools).