What does a deployment diagram show that a container diagram cannot?
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What is being tested
Whether you understand that logical redundancy and physical redundancy are different things.
The reasoning
A container diagram showing three replicas of a service suggests redundancy. A deployment diagram showing all three in one availability zone shows that the redundancy protects against instance failure only.
That difference is invisible at every other level, and it is the most common gap between intended and actual resilience.
The other questions only it answers
- Where does traffic cross a boundary? Cross-zone and cross-region hops carry latency and transfer charges, and they are frequently unintentional — a service placed in a different zone from its database costs on every request.
- What is the blast radius of losing a zone, a region, an account or a cluster?
- What shares fate through a common dependency — a NAT gateway, a load balancer, a shared cluster that nothing on the logical diagram reveals.
- What is single-instance, which is the fastest way to find unintended single points of failure.
The element most often omitted
The control plane. Identity, secrets management, the deployment pipeline, the artefact registry, observability, DNS control.
If those are single-region while the workload is multi-region, a regional failover cannot be executed — you will be unable to authenticate, deploy or see anything at precisely the moment you need all three. This is the recurring finding of resilience rehearsals across the industry, and it appears on a deployment diagram and nowhere else.
The review it enables
Walk each failure domain and ask what survives its loss. Done before an incident, that exercise finds most resilience gaps in an hour — and it consistently finds the control-plane problem that no architecture review produces, because on paper each component is fine.
The failure to avoid
Drawing the target state while the current state differs, with no indication which is which. A deployment diagram that describes an aspiration is worse than none, because people plan against it.