docs: Add runtime logging SIP

Refs: fermyon#962

Signed-off-by: Konstantin Shabanov <[email protected]>

docs/content/sips/008-logging.md

@@ -0,0 +1,126 @@
+title = "SIP 008 - Runtime Logging"
+template = "main"
+date = "2022-12-09T11:36:36Z"
+---
+
+Summary: Unified runtime logging
+
+Owner: [email protected]
+
+Created: December 09, 2022
+
+## Background
+
+Spin runtime logging is an output produced by running `spin up` command.
+
+
+## Current experience
+
+By default, spin prints into `stdout` only the basic info:
+
+```
+$ spin up
+
+Serving http://127.0.0.1:3000
+Available Routes:
+  hello: http://127.0.0.1:3000/hello
+    A simple component that returns hello.
+```
+
+Application log is implicitly written into `~/.spin/<spin_app>/logs/<component_id>_std{err|out}.log`.
+The log for the spin itself has log level `ERROR` and outputs into `stderr`.
+
+To enable a full logging experience, a developer needs to provide `--follow-all` to duplicate app log into `stderr` and also `RUST_LOG=spin=<log_level>` to see the spin log in the `stderr`.
+
+
+## Proposal
+
+- Set the default log level to `INFO`.
+  `INFO` log level is the most widely used across frameworks. It shouldn't make the output overly verbose, but
+- Set default log destination to `stdout/stderr`.
+- Provide a way for spin apps to emit log messages (besides using `println!`/`eprintln!`).
+  *To consider*: unify WIT with [wasi-logging proposal][].
+- Log `WARN`and `ERROR` into `stderr` and `INFO`, `DEBUG`, `TRACE` into `stdout`.
+- Log level `OFF` disables logging completely.
+
+### Goal
+
+To provide the new baseline that gives foundation for further iterative development of new features and enhancements based on the feedback.
+
+### Configuration
+
+Command-line arguments:
+
+```
+--log-level <LOG_LEVEL>
+    Describes the level of verbosity
+
+    [default: INFO]
+    [possible values: ERROR, WARN, INFO, DEBUG, TRACE, OFF]
+
+--log-timezone <LOG_TIMEZONE>
+    [possible values: local, utc]
+```
+
+### Format
+
+Conforms to the default format of the `tracing_subscriber`: `<rfc_3339_datetime>  <log-level> <crate::module>: <text>`.
+
+Severity levels:
+
+- ERROR
+- WARN
+- INFO
+- DEBUG
+- TRACE
+
+### Examples
+
+```
+spin/examples/http-rust $ spin up
+2022-12-16T15:36:17.428429Z  INFO spin_http: Serving http://127.0.0.1:3000
+2022-12-16T15:36:17.428429Z  INFO spin_http: Available Routes:
+  hello: http://127.0.0.1:3000/hello
+    A simple component that returns hello.
+2022-12-16T15:36:21.897190Z  INFO spin_http: Processing request for application spin-hello-world on URI http://localhost:3000/hello
+2022-12-16T15:36:21.897190Z  DEBUG spin_hello_world::hello Request headers: {"host": "localhost:3000", "user-agent": "curl/7.86.0", "accept": "*/*", "spin-path-info": "", "spin-full-url": "http://localhost:3000/hello", "spin-matched-route": "/hello", "spin-base-path": "/", "spin-raw-component-route": "/hello", "spin-component-route": "/hello"}
+2022-12-16T15:36:21.898652Z  INFO spin_http::spin: Request finished, sending response with status code 200 OK
+```
+
+
+## Future design considerations
+
+- Different prod/dev modes
+  * Timezone - Dev: localtime; Prod: UTC
+  * Severity - Dev: INFO; Prod: WARN
+
+- Configuration through a config file
+
+`spin.toml`:
+```toml
+[variables]
+log = {
+  level: "INFO",
+  timezone: "local"
+}
+```
+
+Per component configuration:
+
+`spin.toml`:
+```toml
+[[component]]
+id = "hello"
+log = {
+  level: "OFF",
+}
+```
+
+- Output format customization
+  It might be JSON or some other format.
+
+- Log format customization
+  A user might want to change log record format or datetime format.
+
+
+[wasi-logging proposal]: https://github.com/WebAssembly/wasi-logging

docs/content/sips/index.md

@@ -18,3 +18,4 @@ Here is a list of accepted SIPs:
 - [Application Manifest Redesign](../sips/005-manifest-redesign.md)
 - [Spin Plugins](../sips/006-spin-plugins.md)
 - [Deployment Authentication and Authorisation](../sips/007-deployment-auth.md)
+- [Logging](../sips/008-logging.md)