docs: remove architecture diagram (#3615)

The diagram was more confusion than helpful.

docs/about/architecture.md

@@ -0,0 +1,67 @@
+# Architecture
+
+## Agents
+
+An agent is the Coder service that runs within a user's remote workspace.
+It provides a consistent interface for coderd and clients to communicate
+with workspaces regardless of operating system, architecture, or cloud.
+
+It offers the following services along with much more:
+
+- SSH
+- Port forwarding
+- Liveness checks
+- `startup_script` automation
+
+## Service Bundling
+
+While coderd, provisionerd and Postgres can be orchestrated independently,
+our default installation paths bundle them all together into one system service.
+It's perfectly fine to run a production deployment this way, but there are
+certain situations that necessitate decomposition:
+
+- Reducing global client latency (distribute coderd and centralize database)
+- Running untrusted provisioners (separate provisionerd from nodes with DB access)
+- Achieving greater availability and efficiency (horizontally scale individual services)
+
+## coderd
+
+coderd is the service created by running `coder server`. It is a thin
+API that connects workspaces, provisioners and users. coderd stores its state in
+Postgres and is the only service that communicates with Postgres.
+
+It offers:
+
+- Dashboard
+- HTTP API
+- Dev URLs (HTTP reverse proxy to workspaces)
+- Workspace Web Applications (e.g easily access code-server)
+- Agent registration
+
+## provisionerd
+
+provisionerd is the execution context for infrastructure modifying providers.
+At the moment, the only provider is Terraform (running `terraform`).
+
+Since the provisionerd can be separated from coderd, it can run the provider
+in a myriad of ways on the same Coder deployment. For example, provisioners
+can have different `terraform` versions to satisfy the requirements of different
+templates.
+
+Separability is also advantageous for security. Since provisionerd has no
+database access, infrastructure admins that are not necessarily Coder admins
+can be safely given access to the provisionerd node. As Coder scales and
+multiple infrastructure teams appear, each can be given access to their own
+set of provisionerd nodes, with each set of nodes having their own cloud credentials.
+
+## Workspaces
+
+At the highest level, a workspace is a set of cloud resources. These resources
+can be VMs, Kubernetes clusters, storage buckets, or whatever else Terraform
+lets you dream up.
+
+The resources that run the agent are described as _computational resources_,
+while those that don't are called _peripheral resources_.
+
+Each resource may also be _persistent_ or _ephemeral_ depending on whether
+they're destroyed on workspace stop.