chore(kb/loki): review and expand

knowledge base/logging.md

@@ -2,46 +2,40 @@
 
 > TODO
 
-Intro
+Recording of events or actions.
 
 <!-- Remove this line to uncomment if used
 ## Table of contents <!-- omit in toc -->
 
 1. [TL;DR](#tldr)
+1. [Level](#level)
 1. [Further readings](#further-readings)
    1. [Sources](#sources)
 
 ## TL;DR
 
-<!-- Uncomment if used
-<details>
-  <summary>Setup</summary>
+Usually composed at least by:
 
-```sh
-```
+- Timestamp.
+- Level (A.K.A. Severity).
+- Message.
+- Other metadata.
 
-</details>
--->
+Long term storage is frequently cause of concern.<br/>
+Analysis and search is extremely difficult and computationally expensive at scale.<br/>
+Locality and standardization are often issues, with each application storing their own logs in their own format on their
+own files in different locations. Finding a way to bring all those into a central location for analysis is one of the
+goals of aggregation solutions.
 
-<!-- Uncomment if used
-<details>
-  <summary>Usage</summary>
+## Level
 
-```sh
-```
-
-</details>
--->
-
-<!-- Uncomment if used
-<details>
-  <summary>Real world use cases</summary>
-
-```sh
-```
-
-</details>
--->
+| Level       | Summary                                                                                            |
+| ----------- | -------------------------------------------------------------------------------------------------- |
+| Debug       | **Detailed** contextual information used during development or for troubleshooting                 |
+| Information | Normal, expected events                                                                            |
+| Warning     | Situations that are unexpected but not errors; can potentially lead to problems if ignored         |
+| Error       | Issues that need immediate attention, but might not require termination of operations              |
+| Critical    | Failures or events that require immediate and decisive attention, where operations cannot continue |
 
 ## Further readings
 
@@ -52,6 +46,8 @@ Intro
 ### Sources
 
 - [Distributed logging for Microservices]
+- [Intro to Logging | Zero to Hero: Loki | Grafana]
+- [Structure of Logs (Part 1) | Zero to Hero: Loki | Grafana]
 
 <!--
   Reference
@@ -69,3 +65,5 @@ Intro
 <!-- Upstream -->
 <!-- Others -->
 [distributed logging for microservices]: https://www.geeksforgeeks.org/distributed-logging-for-microservices/
+[Intro to Logging | Zero to Hero: Loki | Grafana]: https://www.youtube.com/watch?v=TLnH7efQNd0
+[Structure of Logs (Part 1) | Zero to Hero: Loki | Grafana]: https://www.youtube.com/watch?v=cnhnoFz6xu0