docs: add emqx_telemetry README

apps/emqx_modules/README.md

@@ -1,7 +1,7 @@
 # EMQX Modules
 
 The application provides some minor functional modules that are not included in the MQTT
-protocol standard, including "Delayed Publish", "Topic Rewrite", "Topic Metrics" and "Telemetry".
+protocol standard, including "Delayed Publish", "Topic Rewrite", "Topic Metrics".
 
 
 ## Delayed Publish
@@ -42,12 +42,4 @@ See HTTP API docs to [List all monitored topics](https://www.emqx.io/docs/en/v5.
 and [Get the monitored result](https://www.emqx.io/docs/en/v5.0/admin/api-docs.html#tag/MQTT/paths/~1mqtt~1topic_metrics~1%7Btopic%7D/get).
 
 
-## Telemetry
 
-Telemetry is used for collecting non-sensitive information about the EMQX cluster.
-
-More introduction about [Telemetry](https://www.emqx.io/docs/en/v5.0/telemetry/telemetry.html#telemetry).
-
-See HTTP API docs to [Enable/Disable telemetry](https://www.emqx.io/docs/en/v5.0/admin/api-docs.html#tag/Telemetry/paths/~1telemetry~1status/put),
-[Get the enabled status](https://www.emqx.io/docs/en/v5.0/admin/api-docs.html#tag/Telemetry/paths/~1telemetry~1status/get)
-and [Get the data of the module collected](https://www.emqx.io/docs/en/v5.0/admin/api-docs.html#tag/Telemetry/paths/~1telemetry~1data/get).

apps/emqx_telemetry/README.md

@@ -0,0 +1,55 @@
+# emqx_telemetry
+
+In order for EMQ to understand how EMQX opensource edition is being used,
+this app reports some telemetry data to [EMQ's telemetry server](https://telemetry.emqx.io/api/telemetry)
+
+To turn it off, you can set `telemetry.enable = false` in emqx.conf,
+or start EMQX with environment variable `EMQX_TELEMETRY__ENABLE=false`.
+
+## Reported Data
+
+This application is only relesaed in EMQX opensource edition.
+There is nothing in the reported data which can back-track the origin.
+The report interval is 7 days, so there is no performance impact.
+
+Here is the full catalog of the reported data.
+
+### Installation
+
+- EMQX version string
+- License (always stubed with "opensource")
+- VM Stats (number of cores, total memory)
+- Operating system name
+- Operating system version
+- Erlang/OTP version
+- Number of enabled plugins
+- Cluster UUID (auto-generated random ID)
+- Node UUID (auto-generated random ID)
+
+### Provisioning
+
+- Advanced MQTT features
+  - Number of retained messages
+  - Number of topic-rewrite rules
+  - Number of delay-publish messages
+  - Number of auto-subscription rules
+- Enabled authentication and authorization mechanisms
+- Enabled gateway names
+- Enabled bridge types
+- Enabled exhooks (the number of endpoints and hookpoints)
+
+### Runtime
+
+- Uptime (how long the server has been running since last start/restart)
+- Number of connected clients
+- Number of messages sent
+- Messaging rates
+
+
+## More info
+
+More introduction about [Telemetry](https://www.emqx.io/docs/en/v5.0/telemetry/telemetry.html#telemetry).
+
+See HTTP API docs to [Enable/Disable telemetry](https://www.emqx.io/docs/en/v5.0/admin/api-docs.html#tag/Telemetry/paths/~1telemetry~1status/put),
+[Get the enabled status](https://www.emqx.io/docs/en/v5.0/admin/api-docs.html#tag/Telemetry/paths/~1telemetry~1status/get)
+and [Get the data of the module collected](https://www.emqx.io/docs/en/v5.0/admin/api-docs.html#tag/Telemetry/paths/~1telemetry~1data/get).