Fix broken internal links

Audited all 206 markdown files (2,774 links) plus the redirects in
.gitbook.yaml, and fixed every internal link that does not resolve.
External URLs are out of scope here and will be handled separately.

Path fixes:

* installation/install-calyptia-fluentd/: the four install guides live
  one directory deeper than the links assume, so `../` was missing one
  level (51 links). Now matches the sibling install-fluent-package/
  guides, which already use `../../` and `../before-install.md`.
* installation/install-fluent-package/install-by-dmg-fluent-package.md:
  same problem on the link to install-by-gem.md.
* installation/install-by-{deb,rpm}-td-agent-v4.md: the td-agent version
  comparison page is in appendix/, not quickstart/.
* how-to-guides/apache-to-s3.md, how-to-guides/http-to-td.md: missing
  `.md` extension.
* appendix/README.md: SUMMARY.md listed this file but it did not exist,
  so the Appendix section had no landing page. Added one.

Anchor fixes, verified against the ids actually rendered on
docs.fluentd.org:

* deployment/system-config.md: `#Recovery` -> `#recovery`.
* output/forward.md: `#how-to-enable-tls/ssl-encryption` ->
  `#how-to-enable-tls-encryption` (2 links); the heading in
  input/forward.md is "How to Enable TLS Encryption".
* filter/README.md, formatter/README.md: the "Filter Plugins" and "Text
  Formatter Plugins" sections no longer exist in
  plugin-development/README.md. Point at api-plugin-filter.md and
  api-plugin-formatter.md instead.

Redirect fixes in .gitbook.yaml:

Most redirect targets name paths that no longer exist in the repository,
but GitBook tracks those file moves internally and resolves them anyway.
Three do not, because the pages were never at the recorded path, so the
old URLs return 404. Point them at the current paths:

* v1.0/articles/out_opensearch -> output/opensearch.md
* v1.0/articles/formatter_tsv -> formatter/tsv.md
* v1.0/articles/api-plugin-helper-metrics ->
  plugin-helper-overview/api-plugin-helper-metrics.md

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Signed-off-by: Shizuo Fujita <fujita@clear-code.com>

Author: Watson1978

.gitbook.yaml

@@ -103,7 +103,7 @@ redirects:
   v1.0/articles/out_exec: plugins/output/exec.md
   v1.0/articles/out_mongo_replset: plugins/output/mongo_replset.md
   v1.0/articles/out_relabel: plugins/output/relabel.md
-  v1.0/articles/out_opensearch: plugins/output/opensearch.md
+  v1.0/articles/out_opensearch: output/opensearch.md
 
   # Plugin/Filter
   v1.0/articles/filter_geoip: plugins/filter/geoip.md
@@ -136,7 +136,7 @@ redirects:
   v1.0/articles/formatter_single_value: plugins/formatter/single_value.md
   v1.0/articles/formatter_json: plugins/formatter/json.md
   v1.0/articles/formatter_stdout: plugins/formatter/stdout.md
-  v1.0/articles/formatter_tsv: plugins/formatter/tsv.md
+  v1.0/articles/formatter_tsv: formatter/tsv.md
 
   # Plugin/Buffer
   v1.0/articles/buffer-plugin-overview: plugins/buffer/README.md
@@ -204,7 +204,7 @@ redirects:
   v1.0/articles/api-plugin-helper-storage: developer/api-plugin-helper-storage.md
   v1.0/articles/api-plugin-helper-socket: developer/api-plugin-helper-socket.md
   v1.0/articles/api-plugin-helper-http_server: developer/api-plugin-helper-http_server.md
-  v1.0/articles/api-plugin-helper-metrics: developer/api-plugin-helper-metrics.md
+  v1.0/articles/api-plugin-helper-metrics: plugin-helper-overview/api-plugin-helper-metrics.md
 
   # Obsolete Pages
   v1.0/categories/data-analytics: README.md

appendix/README.md

@@ -0,0 +1,10 @@
+# Appendix
+
+This section collects supplementary articles that do not fit into the other sections, such as migration guides and comparisons between the discontinued `td-agent` versions.
+
+## Articles
+
+* [Update from v0.12 to v1](update-from-v0.12.md): how to update Fluentd to v1.0 from v0.12 or earlier.
+* [td-agent v2 vs v3 vs v4](td-agent-v2-vs-v3-vs-v4.md): differences between the `td-agent` series, kept for reference. Note that `td-agent` has already reached End of Life \(EOL\); use [`fluent-package`](../installation/install-fluent-package/) instead.
+
+If this article is incorrect or outdated, or omits critical information, please [let us know](https://github.com/fluent/fluentd-docs-gitbook/issues?state=open). [Fluentd](http://www.fluentd.org/) is an open-source project under [Cloud Native Computing Foundation \(CNCF\)](https://cncf.io/). All components are available under the Apache 2 License.

deployment/system-config.md

@@ -328,7 +328,7 @@ See [Output Plugins - overflow_action](../output#overflow_action) for details.
 | :---   | :---                                   | :---    |
 | string | nil (use unique path for the instance) | 1.18.0  |
 
-Set this option when recovering buffers ([Source Only Mode - Recovery](source-only-mode.md#Recovery)).
+Set this option when recovering buffers ([Source Only Mode - Recovery](source-only-mode.md#recovery)).
 
 See [Buffer Plugins - file - path](../buffer/file.md#path) for details.
 

filter/README.md

@@ -53,7 +53,7 @@ Like the `<match>` directive for output plugins, `<filter>` matches against a ta
 
 Only the events whose `message` field contains `cool` get the new field `hostname` with the machine's hostname as its value.
 
-Users can create their own custom plugins with a bit of Ruby. See [this section](../plugin-development/#filter-plugins) for more information.
+Users can create their own custom plugins with a bit of Ruby. See [this section](../plugin-development/api-plugin-filter.md) for more information.
 
 ## Filter Chain Optimization
 

formatter/README.md

@@ -48,7 +48,7 @@ The output changes to
 
 i.e., each line is a single JSON object without "time" and "tag" fields. If you want to include "time" and "tag", use [Inject section](../configuration/inject-section.md).
 
-See [this section](../plugin-development/#text-formatter-plugins) to learn how to develop a custom formatter.
+See [this section](../plugin-development/api-plugin-formatter.md) to learn how to develop a custom formatter.
 
 ## List of Built-in Formatters
 

how-to-guides/apache-to-s3.md

@@ -37,7 +37,7 @@ You can install Fluentd via major packaging systems.
 
 ### Install plugin
 
-If [`out_s3` (fluent-plugin-s3)](../output/s3) is not installed yet, please install it manually.
+If [`out_s3` (fluent-plugin-s3)](../output/s3.md) is not installed yet, please install it manually.
 
 See [Plugin Management](../installation/post-installation-guide.md#plugin-management) section for how to install fluent-plugin-s3 on your environment.
 

how-to-guides/http-to-td.md

@@ -35,7 +35,7 @@ You can install Fluentd via major packaging systems.
 
 If `out_td` (fluent-plugin-td) is not installed yet, please install it manually.
 
-See [Plugin Management](../installation/post-installation-guide#plugin-management) section for how to install fluent-plugin-td on your environment.
+See [Plugin Management](../installation/post-installation-guide.md#plugin-management) section for how to install fluent-plugin-td on your environment.
 
 {% hint style='info' %}
 If you use `fluent-package`, out_td (fluent-plugin-td) is bundled by default.

installation/install-by-deb-td-agent-v4.md

@@ -8,7 +8,7 @@ Fluentd is written in Ruby for flexibility, with performance-sensitive parts in
 
 That is why [Treasure Data, Inc](http://www.treasuredata.com/) provides **the stable distribution of Fluentd**, called `td-agent`. The differences between Fluentd and `td-agent` can be found [here](https://www.fluentd.org/faqs).
 
-This installation guide is for `td-agent` v4. `td-agent` v4 uses fluentd v1 in the core. See [this page](../quickstart/td-agent-v2-vs-v3-vs-v4.md) for the comparison and supported OS.
+This installation guide is for `td-agent` v4. `td-agent` v4 uses fluentd v1 in the core. See [this page](../appendix/td-agent-v2-vs-v3-vs-v4.md) for the comparison and supported OS.
 
 ## Installing `td-agent`
 

installation/install-by-rpm-td-agent-v4.md

@@ -8,7 +8,7 @@ Fluentd is written in Ruby for flexibility, with performance-sensitive parts in
 
 That is why [Treasure Data, Inc](http://www.treasuredata.com/) provides **the stable distribution of Fluentd**, called `td-agent`. The differences between Fluentd and `td-agent` can be found [here](https://www.fluentd.org/faqs).
 
-This installation guide is for `td-agent` v4. `td-agent` v4 uses fluentd v1 in the core. See [this page](../quickstart/td-agent-v2-vs-v3-vs-v4.md) for the comparison and supported OS.
+This installation guide is for `td-agent` v4. `td-agent` v4 uses fluentd v1 in the core. See [this page](../appendix/td-agent-v2-vs-v3-vs-v4.md) for the comparison and supported OS.
 
 ## How to install `td-agent`
 

installation/install-calyptia-fluentd/install-by-deb-calyptia-fluentd.md

@@ -12,11 +12,11 @@ That is why Chronosphere (formerly Calyptia) provides **the alternative stable d
 
 ### Step 0: Before Installation
 
-Please follow the [Pre-installation Guide](before-install.md) to configure your OS properly.
+Please follow the [Pre-installation Guide](../before-install.md) to configure your OS properly.
 
 ### Step 1: Install from Apt Repository
 
-NOTE: If your OS is not supported, consider [gem installation](install-by-gem.md) instead.
+NOTE: If your OS is not supported, consider [gem installation](../install-by-gem.md) instead.
 
 A shell script is provided to automate the installation process for each version. The shell script registers a new apt repository at `/etc/apt/sources.list.d/calyptia-fluentd.sources` and installs the `calyptia-fluentd` deb package.
 
@@ -94,14 +94,14 @@ $ sudo tail -n 1 /var/log/calyptia-fluentd/calyptia-fluentd.log
 You are now ready to collect real logs with Fluentd. Refer to the following tutorials on how to collect data from various sources:
 
 * Basic Configuration
-  * [Config File](../configuration/config-file.md)
+  * [Config File](../../configuration/config-file.md)
 * Application Logs
-  * [Ruby](../language-bindings/ruby.md), [Java](../language-bindings/java.md), [Python](../language-bindings/python.md), [PHP](../language-bindings/php.md),
+  * [Ruby](../../language-bindings/ruby.md), [Java](../../language-bindings/java.md), [Python](../../language-bindings/python.md), [PHP](../../language-bindings/php.md),
 
-    [Perl](../language-bindings/perl.md), [Node.js](../language-bindings/nodejs.md), [Scala](../language-bindings/scala.md)
+    [Perl](../../language-bindings/perl.md), [Node.js](../../language-bindings/nodejs.md), [Scala](../../language-bindings/scala.md)
 * Examples
-  * [Store Apache Log into Amazon S3](../how-to-guides/apache-to-s3.md)
-  * [Store Apache Log into MongoDB](../how-to-guides/apache-to-mongodb.md)
-  * [Data Collection into HDFS](../how-to-guides/http-to-hdfs.md)
+  * [Store Apache Log into Amazon S3](../../how-to-guides/apache-to-s3.md)
+  * [Store Apache Log into MongoDB](../../how-to-guides/apache-to-mongodb.md)
+  * [Data Collection into HDFS](../../how-to-guides/http-to-hdfs.md)
 
 If this article is incorrect or outdated, or omits critical information, please [let us know](https://github.com/fluent/fluentd-docs-gitbook/issues?state=open). [Fluentd](http://www.fluentd.org/) is an open-source project under [Cloud Native Computing Foundation \(CNCF\)](https://cncf.io/). All components are available under the Apache 2 License.