Why start with context
A context diagram names the people and systems around yours before any technology is chosen. It turns the system boundary into a decision rather than an accident, and it gives business and engineering stakeholders one picture they can both correct.
Containers before components
The container view shows the deployable pieces and how they talk. It is the level where most early trade-offs live: one service or several, a queue or a direct call, which data store owns what.
// a background worker is a container decision, not an implementation detail builder.Services.AddHangfire(cfg => cfg.UseSqlServerStorage(connectionString)); builder.Services.AddHangfireServer();
Diagrams and decisions
Every arrow worth drawing usually hides a decision worth recording. Pair the container view with short Architecture Decision Records: context, options, the choice, and what would make you revisit it.
Clarity is a deliverable. Trade-offs are part of the work.
A worked decision
Take the background worker above. On the container diagram it is either a box inside the web application or a box of its own, and the choice is worth writing down:
Reports and synchronization jobs run for minutes and must survive web deployments. The team is small and runs a single SQL Server.
(A) Run Hangfire inside the web application. (B) Run a separate worker service that shares the same Hangfire storage.
Option B. Long jobs no longer compete with web requests for resources, and the web application can be redeployed without interrupting them.
One more deployable to build, monitor and version, and job code must stay compatible with both hosts during a release.
Job volume stays low and the second deployable costs more attention than it saves.
The diagram makes the question visible; the record keeps the reasoning after the people in the room have moved on.
Illustrative example, not a client system.
When to stop drawing
Component diagrams are useful for the parts of the system that are changing or misunderstood. Elsewhere, the code and the tests are the more accurate documentation.