writing-flow-component-documentation.md

Writing documentation for Flow components

This guide outlines best practices for writing reference documentation for Flow components.

Component reference documentation is stored in docs/sources/flow/reference/components, and published to Grafana's documentation website.

Documentation for a component should follow best practices as much as possible so that things are kept consistent. Exceptions can be made when needed; see the list of Exceptions at the bottom of this page for examples.

General guidelines

• Follow the Grafana Writers' Toolkit.

• Follow the Google developer documentation style guide.

• Prefer being explicit over making assumptions; assume that your documentation may be the first page someone visits.

• Aim for component documentation to be consistent with documentation for other components.

• Refer to the component by its full name as much as possible rather than "the component."

• Do not use backticks in headers.

Page structure

Component reference pages should start with YAML frontmatter containing the name of the component as the page title:

---
title: COMPONENT_NAME
---

If documenting a beta component, include the following inside the frontmatter:

labels:
  stage: beta

If documenting an experimental component, include the following inside the frontmatter:

labels:
  stage: experimental

All component reference pages should always be broken down into the following sections:

1. Title

2. Usage

3. Arguments

4. Blocks

5. Exported fields

6. Component health

7. Debug information

8. Debug metrics

9. Examples

If a section does not apply to a component (such as a component not exposing any debug information), the section should still be included, with a sentence explicitly documenting that it does not apply to a component. For example:

## Debug information

`COMPONENT_NAME` does not expose any component-specific debug information.

Always including the headers removes as much guesswork as possible from readers, so they know for certain that there is no debug information, rather than assuming it must not exist if it's not documented.

Title

The Title section is an h1 section which provides a brief description of the component. The header should be named after the component. For example:

# local.file

`local.file` exposes the contents of a file on disk to other components.

The most common use of `local.file` is to load secrets (e.g., API keys) from
files.

Use backticks when referring to the component in the body of the Title section, but do not use backticks in the header.

The Title section should be kept high-level and as small as possible. Detailed information on component behavior should be kept to Arguments and Blocks sections as appropriate.

If your component supports labels, add the following as the last paragraph of the Title section:

Multiple `COMPONENT_NAME` components can be specified by giving them different
labels.

If documenting a beta component, include the following after the header, but before the description of the component:

{{< docs/shared lookup="flow/stability/beta.md" source="agent" >}}

If documenting an experimental component, include the following instead:

{{< docs/shared lookup="flow/stability/experimental.md" source="agent" >}}

Usage

The Usage section provides a minimal example containing required attributes and blocks to configure a component.

It starts with an h2 header called Usage.

The Usage section should be composed of a single River code block, with no description. Use YELLING_SNAKE_CASE to refer to values the user must replace. For example:

## Usage

```river
phlare.scrape "LABEL" {
  targets    = TARGET_LIST
  forward_to = RECEIVER_LIST
}
```

Arguments

The Arguments section details the set of arguments the component supports, followed by a detailed descriptions of how the arguments modify the component behavior. The section starts with an h2 header called Arguments.

If the component does not support any arguments, and is only configured through blocks, the content of the section should be the following paragraph:

The `COMPONENT_NAME` component does not support any arguments, and is configured
fully through child blocks.

When arguments are supported by the component, the set of arguments should be listed using a Markdown table, with the following columns:

Column	Description
Name	Argument name.
Type	Argument type.
Description	Argument description.
Default	Default value for the argument.
Required	Whether the argument is required.

A paragraph with the content "The following arguments are supported:" should always prefix the arguments table.

For example:

The following arguments are supported:

Name             | Type       | Description                            | Default      | Required |
---------------- | ---------- | -------------------------------------- | ------------ | -------- |
`filename`       | `string`   | Path of the file on disk to watch.     |              | yes      |
`detector`       | `string`   | Which file change detector to use.     | `"fsnotify"` | no       |
`poll_frequency` | `duration` | How often to poll for file changes.    | `"1m"`       | no       |
`is_secret`      | `bool`     | Marks the file as containing a secret. | `false`      | no       |

Values for the Name column should be the backticked argument name, such as `targets`.

Values for the Type column should be the backticked River type (for example, string, bool, number). Arrays should be represented as list(INNER_TYPE), and dictionaries should be represented as map(VALUE_TYPE).

In addition to the known types, the following are excepted as convention:

• duration: A string which is parsed as a duration.

• secret: A string which is treated as sensitive.

• capsule(T): An internal encapsulated value.

Values for the Description column should be kept as short as possible to keep the table small and readable. Detailed descriptions should be placed outside of the table. Use full sentences for argument descriptions, ending them in periods.

Values for the Default column may be omitted if the default is the zero value for the given River type. The Default column must be empty for required attributes.

Values for the Required column must be either "yes" (for required attributes) or "no" (for optional attributes).

The set of documented attributes should only contain attributes in the root block of the component. The list of supported blocks and the list of attributes for those blocks are documented in other sections.

It is not required for cells in the Markdown table to be aligned with whitespace.

A detailed description of component behavior and how arguments affect that component behavior should follow the arguments table. To refer to an argument, use The `ARGUMENT_NAME` argument to make it extremely clear what you're referring to.

Descriptions for component behavior should be limited to what is directly relevant to the arguments. If there is component behavior relevant to a specific block, describe that component behavior in the documentation section for that block instead.

It is acceptable to provide Flow configuration snippets for the arguments if it aids documentation.

Blocks

The Blocks section details the hierarchy of blocks the component supports. The section starts with an h2 header called Blocks.

If the component does not support any blocks, the content of the section should be the following paragraph:

The `COMPONENT_NAME` component does not support any blocks, and is configured
fully through arguments.

When blocks are supported by the component, the set of blocks should be listed using a Markdown table, with the following columns:

Column	Description
Hierarchy	Block path.
Block	Link to block documentation.
Description	Block description.
Required	Whether the block is required.

For example:

The following blocks are supported:

Hierarchy                    | Block             | Description                        | Required |
---------------------------- | ----------------- | ---------------------------------- | -------- |
client                       | [client][]        | HTTP client settings.              | no       |
client > basic_auth          | [basic_auth][]    | Basic authentication settings.     | no       |
client > authorization       | [authorization][] | Generic authentication settings.   | no       |
client > oauth2              | [oauth2][]        | OAuth 2.0 authentication settings. | no       |
client > oauth2 > tls_config | [tls_config][]    | TLS settings for OAuth 2.0.        | no       |
client > tls_config          | [tls_config][]    | TLS settings the HTTP client.      | no       |

Values for the Hierarchy column should be the path to the block from the component. Use the > character to represent nested blocks. Do not surround the value in backticks, as it looks strange when rendered to the table.

Values for the Block column should contain a link to the header in the same documentation page which describes the block. Do not link to another component page that happens to have the same block; prefer re-documenting blocks and being explicit instead of having users jump around. Use the docs/shared shortcode to de-duplicate block definitions across multiple components.

Values for the Description column should be kept as short as possible to keep the table small and readable. Use full sentences for block descriptions, ending them in periods.

Values for the Required column should be the text "yes" (for required blocks) or "no" (for optional blocks).

If nested blocks are used in the blocks table (like client > basic_auth in the example), a description of what the > symbol means should be included in the following paragraph after the block table:

The `>` symbol indicates deeper levels of nesting. For example,
`PARENT_BLOCK > CHILD_BLOCK` refers to a `CHILD_BLOCK` block defined inside
an `PARENT_BLOCK` block.

When including this paragraph, replace PARENT_BLOCK and CHILD_BLOCK with block names from your component to provide a concrete example of what the hierarchy represents.

A paragraph with the content "The following blocks are supported:" should always prefix the blocks table.

A set of sub-sections for each defined block should follow the Blocks section. Each unique block type will only have one Block section, regardless of how many times that block type appears in the blocks table. See Block section for a description on these sections.

Block section

The Block section is a sub-section of Blocks describing an individual block supported by a component. There is one Block section per recognized block type within the component.

The Block section starts with an h3 header with the name of the block, followed by the word "block." Do not surround the name of the block in backticks in the header.

Block sections are similar to Arguments section, where it is composed of:

1. A brief description of the block.

2. A table of arguments supported by the block.

3. Detailed description for how that block impacts component behavior, and how the block's arguments can be used to modify that behavior.

See Arguments for a description of how to write the arguments table and block-level descriptions following that table.

For example:

### tls block

The `tls` block configures TLS settings used when connecting to the server. If
the `tls` block isn't provided, connections to the server are unencrypted.

The following arguments are supported:

Name              | Type       | Description                                                   | Default | Required |
----------------- | ---------- | ------------------------------------------------------------- | ------- | -------- |
`ca_file`         | `string`   | Path to the CA file.                                          |         | no       |
`cert_file`       | `string`   | Path to the TLS certificate.                                  |         | no       |
`key_file`        | `string`   | Path to the TLS certificate key.                              |         | no       |
`min_version`     | `string`   | Minimum acceptable TLS version for connections.               |         | no       |
`max_version`     | `string`   | Maximum acceptable TLS version for connections.               |         | no       |
`reload_interval` | `duration` | Frequency to reload the certificates.                         |         | no       |
`client_ca_file`  | `string`   | Path to the CA file used to authenticate client certificates. |         | no       |

Default values for the `min_version` and `max_version` arguments are inherited
from Go, currently TLS 1.2 and TLS 1.3 respectively. When these arguments are
not provided, their Go-inherited defaults will not display in the component UI
page.

It is acceptable for block sections to provide Flow configuration snippets for the block if it aids documentation.

Exported fields

The Exported fields section details a list of fields which the component exports. The section starts with an h2 header called Exported fields.

If the component does not export any fields, the content of the section should be the following paragraph:

The `COMPONENT_NAME` component does not export any values.

When the component exports values, it should provide a table of exported values with the following columns:

Column	Description
Name	Name of exported value.
Type	River type of exported value.
Description	Description of exported value.

Values for the Name column should be the backticked exported field name, such as `targets`.

Values for the Type column should be the backticked River type. These types should follow the same guidelines detailed in the Type column in the Arguments block.

Values for the description column should be kept as short as possible to keep the table small and readable.

A paragraph with the content "The following fields are exported and can be referenced by other components:" should always prefix the exported fields table.

Following the exported fields table, a longer description of each exported fields may be provided, but this normally isn't done.

Component health

The Component health section describes when the component is healthy. The section starts with an h2 header called Component health.

If the component does not have special health logic, the content of the section should be the following paragraph:

`COMPONENT_NAME` is only reported as unhealthy if given an invalid
configuration.

Otherwise, write a detailed description for when the component is reported as healthy.

Debug information

The Debug information section describes debug information exposed in the Grafana Agent Flow UI. The section starts with an h2 header called Debug information.

If the component does not expose any debug information, the content of the section should be the following paragraph:

`COMPONENT_NAME` does not expose any component-specific debug information.

Otherwise, write a high-level description for what debug information the component provides. Do not document the attributes or blocks which are exposed through the debug information.

Debug metrics

The Debug metrics section describes what Prometheus metrics are exposed by a component. The section starts with an h2 header called Debug metrics.

If the component does not expose any debug metrics, the content of the section should be the following paragraph:

`COMPONENT_NAME` does not expose any component-specific debug metrics.

When the component exports values, it should provide a table of exposed metrics with the following columns:

Column	Description
Name	Name of Prometheus metric.
Type	Prometheus metric type.
Description	Metric description.

Values in the Name and Type column should be backticked.

Values in the Type column should be a Prometheus metric type, one of counter, gauge, histogram, native histogram, or summary.

A paragraph with the content "The following Prometheus metrics are exposed:" should always prefix the metrics table.

Examples

The Examples section provides copy-and-paste River pipelines which use the Flow component. The section starts with an h2 header called Examples. If there is only one example, call the section Example instead.

The Examples section should be composed of a brief description of each example, followed by the example in a code block. For example:

This example reads a JSON array of objects from an endpoint and uses them for
the set of scrape targets:

```river
remote.http "targets" {
  url = env("MY_TARGETS_URL")
}

prometheus.scrape "default" {
  targets    = json_decode(remote.http.targets.content)
  forward_to = [prometheus.remote_write.default.receiver]
}

prometheus.remote_write "default" {
  client {
    url = env("PROMETHEUS_URL")
  }
}
```

Each example should be a full pipeline when possible, rather than just the individual component being documented.

If an example includes clarifying comments, make sure that the relevant Arguments or block header includes sufficient explanation to be the official source for the clarifying comment. Clarifying comments must only be used be supplementary information to reenforce knowledge, and not as the primary source of information.

Exceptions

The rules described in this page should be sufficient in most cases for being able to write detailed documentation.

However, there have been some cases where the page structure needed to be changed to properly document a component. The following sections will describe some instances where exceptions had to be made.

loki.source.podlogs

The loki.source.podlogs component documentation needed to add an extra section to document the PodLogs CRD, since we do not yet have a way of documenting auxiliary artifacts which are related to a component.