This README gives an overview of how to build and contribute to the documentation of Apache Flink.

The documentation is included with the source of Apache Flink in order to ensure that you always have docs corresponding to your checked out version. The online documentation at https://flink.apache.org/ is also generated from the files found here.

Requirements

Build the documentation and serve it locally

The Flink documentation uses Hugo to generate HTML files. More specifically, it uses the extended version of Hugo with Sass/SCSS support.

As a pre-requisite, you need to have Go installed. To build the documentation, you can install Hugo locally or use a Docker image.

Both methods require you to execute commands in the directory of this module (docs/). The built site is served at http://localhost:1313/.

Using Hugo Docker image:

$ git submodule update --init --recursive
$ ./setup_docs.sh
$ docker run -v $(pwd):/src -p 1313:1313 jakejarvis/hugo-extended:latest server --buildDrafts --buildFuture --bind 0.0.0.0

Local Hugo installation:

Make sure you have installed Hugo on your system.

$ git submodule update --init --recursive
$ ./setup_docs.sh
$ ./build_docs.sh

The site can be viewed at http://localhost:1313/

Include externally hosted documentation

With the ongoing efforts to move Flink's connectors from this repository to individual, dedicated repositories, this also requires the documentation to be hosted outside this repo. However, we still want to serve all documentation as a whole on the Flink documentation website.

In order to achieve this, we're using Hugo Modules. to create a virtual filesystem.

Adding new externally hosted documentation requires the following steps to be taken:

1. (If necessary) Move the existing documentation to the new repository
2. In this new repository, in the docs folder, create a file go.mod containing:

module github.com/apache/flink-connector-<repositoryname>/docs

go 1.18

Replace with the name of your repository. See https://github.com/apache/flink-connector-elasticsearch/tree/main/docs/go.mod for an example. 3. In this new repository, in the docs folder, create a config.toml file containing:

module:
  mounts:
    - source: content
      target: content
      lang: en
    - source: content.zh
      target: content.zh
      lang: zh

See https://github.com/apache/flink-connector-elasticsearch/tree/main/docs/config.toml for an example.

4. In the Flink repository, edit the docs/setup_docs.sh file and add a reference to your now externally hosted documentation. The reference will look like hugo mod get -u github.com/apache/<reponame>/docs@main

Replace with the name of your repository.

5. In the Flink repository, edit the docs/config.toml file add the files from the external repository as a mount to the Flink documentation. Hugo creates a virtual mount, meaning that any mounted file will appear as if it's located in this repository.

[module]
[[module.imports]]
  path = 'github.com/apache/<repositoryname>/docs'
[[module.imports.mounts]]
  source = 'content'
  target = 'content'
  lang = 'en'
[[module.imports.mounts]]
  source = 'content.zh'
  target = 'content'
  lang = 'zh'

Replace with the name of your repository. The Chinese documentation source content.zh is targetted to the actual content folder. Hugo combines the target and lang to display the correct language. See the current docs/config.toml file for an example.

Generate configuration tables

Configuration descriptions are auto generated from code. To trigger the generation you need to run in the project root:

mvn -Pgenerate-config-docs install -Dfast -DskipTests

The resulting html files will be written to layouts/shortcodes/generated. Tables are regenerated each time the command is invoked. These tables can be directly included into the documentation:

{{< generated/file_name >}}

Contribute

Markdown

The documentation pages are written in Markdown. It is possible to use GitHub flavored syntax and intermix plain html.

Front matter

In addition to Markdown, every page contains a Jekyll front matter, which specifies the title of the page and the layout to use. The title is used as the top-level heading for the page. The default layout is plain (found in _layouts).

---
title: "Title of the Page"
---

---
title: "Title of the Page" <-- Title rendered in the side nave
weight: 1 <-- Weight controls the ordering of pages in the side nav. 
type: docs <-- required
aliases:  <-- Alias to setup redirect from removed page to this one
  - /alias/to/removed/page.html
---

Structure

Page

Headings

All documents are structured with headings. From these headings, you can automatically generate a page table of contents (see below).

# Level-1 Heading  <- Used for the title of the page 
## Level-2 Heading <- Start with this one for content
### Level-3 heading
#### Level-4 heading
##### Level-5 heading

Please stick to the "logical order" when using the headlines, e.g. start with level-2 headings and use level-3 headings for subsections, etc. Don't use a different ordering, because you don't like how a headline looks.

Table of Contents

Table of contents are added automatically to every page, based on heading levels 2 - 4. The ToC can be omitted by adding the following to the front matter of the page:

---
bookToc: false
---

ShortCodes

Flink uses shortcodes to add custom functionality to its documentation markdown. The following are available for use:

Flink Artifact

{{< artifact flink-streaming-scala withScalaVersion >}}

This will be replaced by the maven artifact for flink-streaming-scala that users should copy into their pom.xml file. It will render out to:

<dependency>
    <groupId>org.apache.flink</groupId>
    <artifactId>flink-streaming-scala_2.12</artifactId>
    <version><!-- current flink version --></version>
</dependency>

It includes a number of optional flags:

• withScalaVersion: Includes the scala version suffix to the artifact id
• withTestScope: Includes <scope>test</scope> to the module. Useful for marking test dependencies.
• withTestClassifier: Includes <classifier>tests</classifier>. Useful when users should be pulling in Flink tests dependencies. This is mostly for the test harnesses and probably not what you want.

You can also use the shortcodes (with same flags) instead:

• artifact_gradle to show the Gradle syntax
• artifact_tabs to create a tabbed view, showing both Maven and Gradle syntax

Back to Top

{{< top >}}

This will be replaced by a back to top link. It is recommended to use these links at least at the end of each level-2 section.

Info Hints

{{< hint info >}}
Some interesting information
{{< /hint >}}

The hint will be rendered in a blue box. This hint is useful when providing additional information for the user that does not fit into the flow of the documentation.

Info Warning

{{< hint warning >}}
Something to watch out for. 
{{< /hint >}}

The hint will be rendered in a yellow box. This hint is useful when highlighting information users should watch out for to prevent errors.

Info Danger

{{< hint danger >}}
Something to avoid
{{< /hint >}}

The hint will be rendered in a red box. This hint is useful when highlighting information users need to know to avoid data loss or to point out broken functionality.

Label

{{< label "My Label" >}}

The label will be rendered in an inlined blue box. This is useful for labeling functionality such as whether a SQL feature works for only batch or streaming execution.

Flink version

{{< version >}}

Interpolates the current Flink version

Scala Version

{{< scala_version >}}

Interpolates the default scala version

Stable

{{< stable >}}
 Some content
{{< /stable >}}

This shortcode will only render its content if the site is marked as stable.

Unstable

{{< unstable >}}
Some content 
{{< /unstable >}}

This shortcode will only render its content if the site is marked as unstable.

Query State Warning

{{< query_state_warning >}}

Will render a warning the current SQL feature may have unbounded state requirements.

tab

{{< tabs "sometab" >}}
{{< tab "Java" >}}
```java
System.out.println("Hello World!");
```
{{< /tab >}}
{{< tab "Scala" >}}
```scala
println("Hello World!");
```
{< /tab >}}
{{< /tabs }}

Prints the content in tabs. IMPORTANT: The label in the outermost "tabs" shortcode must be unique for the page.

Github Repo

{{< github_repo >}}

Renders a link to the apache flink repo.

Github Link

{{< gh_link file="/some/file.java" name="Some file" >}}

Renders a link to a file in the Apache Flink repo with a given name.

JavaDocs Link

{{< javadoc file="some/file" name="Some file" >}}

Renders a link to a file in the Apache Flink Java Documentation.

PythonDocs Link

{< pythondoc file="some/file" name="Some file" >}}

Renders a link to a file in the Apache Flink Python Documentation.

FlinkDownloads Link

{{< downloads >}}

Renders a link to the apache flink download page.