Config: classic mode: adding index page

SUMMARY.md

@@ -53,7 +53,7 @@
     * [Upstream servers](administration/configuring-fluent-bit/yaml/upstream-servers-section.md)
     * [Environment variables](administration/configuring-fluent-bit/yaml/environment-variables-section.md)
     * [Includes](administration/configuring-fluent-bit/yaml/includes-section.md)
-  * [Classic mode](administration/configuring-fluent-bit/classic-mode/README.md)
+  * [Classic mode](administration/configuring-fluent-bit/classic-mode.md)
     * [Format and schema](administration/configuring-fluent-bit/classic-mode/format-schema.md)
     * [Configuration file](administration/configuring-fluent-bit/classic-mode/configuration-file.md)
     * [Variables](administration/configuring-fluent-bit/classic-mode/variables.md)

administration/configuring-fluent-bit/classic-mode.md

@@ -0,0 +1,14 @@
+# Configure Fluent Bit using classic mode
+
+Fluent Bit classic mode configuration will be deprecated at the end of 2026.
+
+Classic mode is a custom configuration model for Fluent Bit. It's more limited than the [YAML configuration mode](../configuring-fluent-bit/yaml.md), and doesn't have the more extensive feature support the YAML configuration has. Classic mode basic design only supports grouping sections with key-value pairs and lacks the ability to handle sub-sections or complex data structures like lists.
+
+Learn more about classic mode:
+
+- [Format and schema](./classic-mode/format-schema.md)
+- [Variables](./classic-mode/variables.md)
+- [Configuration file](./classic-mode/configuration-file.md)
+- [Commands](./classic-mode/commands.md)
+- [Upstream servers](./classic-mode/upstream-servers.md)
+- [Record accessor syntax](./classic-mode/record-accessor.md)

administration/configuring-fluent-bit/yaml.md

@@ -4,9 +4,11 @@
 
 ## Before you get started
 
+YAML has become essential in a cloud ecosystem. To minimize friction and provide a more intuitive experience for creating data pipelines, users are encouraged to transition to YAML.
+
 Fluent Bit traditionally offered a `classic` configuration mode, a custom configuration format that's phasing out. While `classic` mode has served well for many years, it has several limitations. Its basic design only supports grouping sections with key-value pairs and lacks the ability to handle sub-sections or complex data structures like lists.
 
-YAML has become essential in a cloud ecosystem. To minimize friction and provide a more intuitive experience for creating data pipelines, users are encouraged to transition to YAML. The YAML format enables features, such as processors, that aren't possible to configure in `classic` mode.
+The YAML format enables features, such as processors, that aren't possible to configure in `classic` mode.
 
 As of Fluent Bit v3.2, you can configure everything in YAML.
 
@@ -43,4 +45,4 @@ To access detailed configuration guides for each section, use the following link
 - [Environment Variables Section documentation](./yaml/environment-variables-section.md)
   - Information on setting environment variables and their scope within Fluent Bit.
 - [Includes Section documentation](./yaml/includes-section.md)
-  - Description on how to include external YAML files.
+  - Description on how to include external YAML files.