chore: add information about the coder agent

images/structure.md

@@ -50,15 +50,13 @@ Coder inserts static assets into each workspace, including:
 
 - code-server
 - JetBrains Projector
-- Coder CLI
+- Coder CLI, which includes the [Coder Agent](../setup/architecture.md)
 
 These assets are installed into the `/var/tmp/coder` directory of each
-workspace. You do not need to include these static assets in your custom
-images. However, the following software are **required** when you build custom
-images:
+workspace. You do not need to include these static assets in your custom images.
+However, the following software are **required** when you build custom images:
 
-- [POSIX
-  Utilities](https://pubs.opengroup.org/onlinepubs/9699919799/idx/utilities.html)
+- [POSIX Utilities](https://pubs.opengroup.org/onlinepubs/9699919799/idx/utilities.html)
 - [GNU libc](https://www.gnu.org/software/libc/libc.html)
   - The minimum GNU libc version supported for the Coder-inserted assets is
     `2.1`

setup/architecture.md

@@ -8,6 +8,9 @@ Coder is deployed on Kubernetes and includes the following components:
 - **coderd**: the central authority; provides authentication and supports the
   Dashboard and an API which you can use to create and interact with Workspaces
 - **PostgreSQL**: data storage for session tokens, workspace information, etc.
+- **coder agent**: a program running in each workspace that connects to `coderd`
+  and handles tunnelled connections, collection of workspace statistics (such as
+  processor and memory utilization), and manages programs, such as editors.
 
 Each component runs in its own Kubernetes pod.
 

workspaces/variables.md

@@ -82,3 +82,46 @@ env | grep CODER_
         <td>The name of the workspace provider hosting the workspace</td>
     </tr>
 </table>
+
+<!-- markdownlint-restore -->
+
+## Other variables
+
+Coder uses the following environment variables for its internal operation:
+
+> **Important**: These variables may be modified or removed in future releases
+> without prior notice and are not covered by Coder's backward compatibility
+> policy. These are documented here for your information only.
+
+<!-- markdownlint-disable MD044 -->
+<table>
+    <tr>
+        <th>Environment variable</th>
+        <th>Description</th>
+    </tr>
+    <tr>
+        <td><code>CODER_AGENT_TOKEN</code></td>
+        <td>The token used by the <a href="../setup/architecture.md">Coder Agent</a>
+            to authenticate with <code>coderd</code>. The Coder Agent handles
+            tunnelled connections, collects workspace statistics (such as
+            processor and memory utilization), and manages programs, such as
+            editors.</td>
+    </tr>
+    <tr>
+        <td><code>CODER_AGENT_URL</code></td>
+        <td>Th URL that the <code>coder agent</code> process uses
+            to connect to <code>coderd</code>. If this is not set, the agent
+            will connect to <code>CODER_URL</code> instead, enabling the
+            <code>coder agent</code> and <code>coder</code> command-line tool
+            to connect to different installations.</td>
+    </tr>
+    <tr>
+        <td><code>CODER_BOOTSTRAP_SCRIPT</code></td>
+        <td>The script used to initiate the workspace startup sequence when the
+            <a href="../admin/workspace-management/self-contained-builds.md">
+            self-contained workspace builds</a> feature is active; begins by
+             downloading the "bootstrap agent" from the <code>coderd</code>
+             process.</td>
+    </tr>
+</table>
+<!-- markdownlint-restore -->